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TDS Software User`s Manual

1. Description IPEE 1560 amp 5 8 Number af Measurements a 8 9 ThirdAxis Label SIME MK TO ThirdAxisStart 1 000E hp Tr ThirdaxisStop i 1 62E 01 12 ThirdAxisStep 45DE oi 15 Mex Y Data O 7 J 1 s ODES OT 14 Min Y Data ODE O Illustration E 15 3D master file in a spreadsheet E 25 Notes on 3D files Sound Lab TDS File formats nil Comments Parameter label Value 3D20A DS Title inn Name SER Date ui Location WU Description B Number of Measurements 36 Third Axis Label TIME Third Axis Start 0 00E 00 Third Axis Stop 1 62E 01 Third Axis Step 4 50E 01 Max Y Data 7 00E 01 Min Y Data 1 00E 01 File version number Always use this key word for 3D measurements Maximum of 50 characters Maximum of 50 characters Maximum of 50 characters Maximum of 50 characters Maximum of 128 characters From 2 100 measurements The Start time value The Stop time value The Time step value Largest data value in all curves Sinallest data value in all curves t Sound Lab TDS Glossary mi Appendix F Glossary acoustic center The point in space of the origin of sound for a sound emitting transducer the point from which the spherical waves appear to diverge as observed at remote points acoustic origin the point
2. The RT60 cursors active only for time response data 4 67 Sound Lab TDS Display Menu iili Other Display options Adjust colors Sixteen colors are available for Sound Labdisplays and menus When you select Adjust Colors a list appears showing various display elements along with their current colors Highlight the item in the left hand list then press Enterto open another sub menu with a list of color choices Make your selection and press Enter Sound Lab will update the color sample in the sub menu Sound Labwill not allow color combinations that will cause display elements to disappear For instance if Window Time Response ETC Frequency Response TDS 3D Haterfall 3D Noise Display Table backgroundis black you may STI RASTI Display Table Add Noise to STI RASTI not set Window text to black Overlay Ctri F2 orf Difference nit ra Off Cursor Fz Off RTE0 Cursor Shift Fz orf ALt Mouse On B lack Alt Beep orf Adiust Display Colors Blue Green Background Color Blue Em Window BkGrnd Color LightGSray Mindow Text Color Black EN Window Key Color Red BN Window Data Color Blue BN Granh 1 Color Hhite Cuan Red Magenta Brown LightGray DarkGray LightBlue LightGreen LightCyan LightRed LightMagenta Yellow Hhite Graph 2 Color LightRed EN Graph Grid Color LightGray Cursor Color White Factory Grau Scale ATt CIose Alt Undo Illustration 4 46 Submenu to adjust dis
3. turn on your machine come to a prompt format a disk e make a backup copy change directories If you are not sure how to perform these tasks refer to your DOS manual before starting the Sound Lab Install program Your TEF Sound Lab package includes all the files and programs necessary for installation While Sound Lab works on both hard drive and floppy based systems a hard drive is recommended Before you install this Sound Lab software make backup copies of your disks and store originals in a safe place Install from the copy which is not write protected This means it can be written to Let s assume that you re installing Sound Lab TDS on your hard disk which is drive C from floppy drive A Put the copy disk in drive A and type A TDSINST Press Enter to continue 2 1 SOUND LAB TDS Installation Program 2 0 Copyright cc 1991 94 TECHHOUN Division of Crown International Inc P D Hox 1000 1718 M Mishawaka Hd Elkhart IN 46515 1000 219 294 8295 Enter destination drive path ENTER Continue ESC Return to DOS 2 2 Sound Lab TDS Install il Copyright screen The copyright screen is first screen you ll see in the Sound Lab Install software Press Enter to continue or sc to return to DOS The second screen asks you to name the destination drive path where you will install the program We recommend that you choose the default drive and directory C 1SL1
4. 5 2 Performing a frequency response test eese eei Reina 5 Noise criteria measurements seseseeseeeeeeeeemeeeenttne tete tetti 5 9 Eq UipiiemtsnCe es n amico oo n Pte cms ar a 5 9 NC measurements with a microphone ccccccnnnnnonoooooconnnnacinccnnncannnanonnss 5 9 NC measurements with sound level meters E cmt 5 10 OO ete Mh S TT 100005 coe EET TURO ee neige eee tre Poe end den 5 13 SMC anal RAS Mop e MMMM eet eat et 5 13 Performing the measurement with calibrated talker speaker 5 15 Equipment arrangement for calibration sssssesessessseessssssssserreereree 5 15 Setting up parameters E 5 16 Arras theeceguipment FORT uocis ont t io laa de 5 19 Driving the system directly M P ae 5 20 Adding noise to STI measurements ccccocconononconnoncconnncnnanenonencnnnanonoss 5 21 Evaluating the STI graph and summary table suus 5 22 STI Suttmaty ta Ble displayi n seer t ettet tH E tote edente 5 23 About the STI measurement process esses 5 25 Introduction t 3D measurement pitisi ane centena i e ed 5 27 Measuring loudspeakers with 3D sees 2728 Measuirine TOGS whi 51D ote tet A ec ee 5 30 Over apatio in 3D displays esceeeer ertet ee eene ren Innen noe 5 31 Section 6 Practice measurements 6 1 i curo TE TSS C aa 6 1 T EIC BLEU e C OTT 6 1 Rendinp Am ETC A a a ces oe 6 3
5. Erase Configuration Printer settings Resolution Output Port Epson FX Graph Size Half Page Illustration 4 8 Printer Settings sub menu TDS Open Old Drive amp Dir Shift F3 Save as Erase Configuration Printer Settings Print Sound Lab z D 10 29 EE Uer 1 16 00 EPROM Uer 30 14 62 Sound Lab TDS File Menu tll About Displaysthe current version and date of the software and the firmware inside the TEF analyzer Illustration 4 9 About sub menu Note The Aboutcommand can be used as a diagnostic tool to check the connection between the PC and the 7 20 91 TEF analyzer If the PC is Crown International Press any key to continue TDS Open Old Drive Dir Shift F23 Save as Erase Configuration Printer Settinas Print About ATA 1 1 RTADEHO Acous taEG SLX Inc analyzer a message will appear The TEF is not ready ROM data is not available Go to Sound Lab is composed of several modules that make up a total measurement package TDS is a module within the Sound Lab family When you start Sound Lab TDS for the first time the TDS module isloaded You choose other modules with the Go to command under the File menu As you install new modules they will appear in the Go to sub menu Quit returns you to DOS After you select Quit a sub menu will appear and ask you Do
6. Header block format Each line of information within the header blocks is usually in the following format e A parameter label in double quotes _ e An ASCII tab character hexadecimal 09 e Avalue The value is in double quotes if it is alphanumeric e An ASCII carriage return character hexadeci mal OD for Macintosh files and a carriage return and line feed for MS DOS files hexa decimal 0D OA Macintosh line format Parameter label tab numeric value lt cr gt MS DOS line format Parameter label lt tab gt numeric value lt cr gt lt lf gt Data block format The data block is usually stored as a voltage measured by the TEF Most files store the voltage as complex number pairs See the data section for each file type for the exact storage format E 1 E 2 Sound Lab TDS File formats TIT ETC file format The ETC header The first part of the ETC file is the header block The header is a record of all analyzer settings that went into making the test Also included in the header are operator comments test location and the date the test was made The ETC header has 29 lines Line 29 is always Data The ETC data The second part of the ETC file is the collected data The data is stored as the voltage measured by the TEF independent of the preamp gain The number of lines in the data part of the file always equals the number of samples selected when the test was made 512 1024 2048 4096
7. Echoes A sound source vibrates against air molecules creating sound waves that travel outward in all directions Some of the sound travels directly to the listener or to a microphone and is called direct sound The rest strikes the walls ceiling floor and furnishings of the recording room At those surfaces some of the sound energy is absorbed some is transmitted through the surface and the rest is reflected back into the room B Sound Lab TDS Basics of Sound mi Since sound waves travel about 1 foot per millisecond the sound reflections arrive after the direct sound reaches the listener The delayed arrival of a reflected sound causes a repetition of the original sound called an echo as Shown in Illustration A 7 In large rooms we sometimes hear discrete single echoes in small rooms we often hear a short rapid succession of echoes evenly spaced in time called flutter echoes Direct sound m mn B E ad pe E E Illustration A 7 Echo A Echo formation B Amplitude vs time of direct sound and echo C Sound Lab TDS Basics of Sound mill Parallel walls or diagonally opposite corners create flutter echoes by reflecting sound back and forth between them many times You can detect flutter echoes by clapping your hands next to one wall and listening for a fluttering sound Since echoes can reduce the clarity of sound they should be eliminated by adding patches of absorbent material or
8. NOISELESS_RASTI a measure ment without noise then use the NO_NOISE key word E 15 Sound Lab TDS File formats Parameter label Value Comments Hile T Name did Date ai Location gt Description iid Volts Per Reference Unit 01 Propagation Speed 1130 00 Distance Unit BEET 5 Distance Units are key words and can only be expressed in one of four key words Note all are upper case FEET INCH METER CENTIMETER 0 Line input B 1 Microphone input B 2 Line input A 3 Microphone input A ie Channel 3 Preamp Gain A 48 Preamp Gain B 0 E 16 C E z Q r Q gt jw 0 File formats ALTARFB 5T1 THT Propagation Speed Distance Unit 4 dei AAA AAA rr AAA H z 7 aeta Illustration E 11 STI and RASTI analyzer settings block E 17 mil Sound Lab TDS File formats Notes on STI summary table block FREQUENCY STI EARLY RT60 S N RATIO 125 Hz 0 85 0 3 10 5 250 Hz 0 7 0 61 6 500 Hz 0 53 1 13 09 1000 Hz 0 47 2 07 1 2000 Hz 0 49 1 71 04 4000 Hz 0 35 3 37 4 4 8000 Hz 034 X 5 34 4 8 OVERALL STI 0 46 EQUIVALENT S N RATIO 1 EQUIVALENT EARLY RT60 2 1 SUBJECTIVE EVALUATION FAIR Subjective evaluations are key E 18 words and can only be expressed in five key word
9. STI measures in the octaves from 125 Hz to 8 kHz e RASTI a shortened version of the STI proce dure measures only at the 500 Hz and 2 kHz octaves Sound Lab STI c llects data from a noise measurement and several time response tests which are processed to yield an overall speech intelligibility prediction The resulting data is displayed on the screen in a graph or table The software default measures with noise included although it can be turned off Practical STI RASTI results however have noise data added into the calculation and Sound Lab TDS allows you to add noise later o 13 Sound Lab TDS Performing measurements STI RASTI mil Sound Lab TDS allows you to make STI measurements by using a calibrated talker speaker placed in the location and position where a human speaker would be This talker speaker must be flat Cunder free field conditions within plus or minus 10 dB between 8 kHz and 11 2 kHz A test microphone is placed in the position of the listener For valid speech intelligibility results the talker speaker should be calibrated to a level that simulates the voice level of a person speaking and equalized to eliminate any deficiencies ofthe speaker This operation preceeds the STI test The Calibration procedure is set up in the Parameters STI sub menu and the Speaker EQ test option automatically follows calibration The calibration and equalization tests automatically precede the STI test when you
10. 906 00000000 OO O 06 06 0 06 0000000000 99 o o O 0O O0 06000000000 0 O O O O 0000090000009 e 6 00 09000000000 60 060 0 O O 00909000000 OO O e O 0O 99 069090000000 O O 06 0 0 609000000009 o e 9 O 906 0000000000 06 6 O 0 06 80 880808008 Ce O e 90606 909000000009 6 06 06 0 06 60 08080008 Ce 4 e 060 00 0000000000 9 O O O O vt000000000009 O e 0 6 60 00000000 00 06 0 06 0 0 0000000000009 4 e 06 0 00 006000008000 O O 06 6 06 000000000099 9 e 0 0 0 090 ecsvccse 00 0O 06 6000000000099 O e ee 00000000 00 9 O O O O 000000000000 0 e 9 ee 00000000 00 O O O O 0 0000000090099 9 e 9096 6900000000 6 06 O O 06 06090000009 9 9 4 00 0000000000 0 060 9 O 060000000090 99 O e 0 906 0000000000 0 O 0 O 0 60000000000 99 O e 0 o 0090 00009000000 O 06 06 6 O 0069009090009 9 O e 060 00 09000000000 O 6 9 O 0600000000009 O e 0 089 0000000000 6 O 06 06 O 0909000000009 O OO O 0O O0 0000000000 0 O O 8 0909090000909 e AIR MOLECULE MOTION Sas WAVE MOTION Illustration A 1 A sound wave is made of high pressure compressions and low pressure rarefactions a compression When the cone moves in it pulls the molecules farther apart forming a rarefaction As illustrated in Illustration A 1 the compressions have a Sound Lab TDS AIR PRESSURE Basics of Sound mil higher pressure than ambient atmospheric pressure the rarefactions have a lower atmosph
11. Assuming you wish to proceed press Enter A third screen appears if TDS SET is not found Sound Lab TDS Install To select a COM port tupe the nunber of the desired COM port or H for the Host Interface option 11 2 or HI Check to be sure TEF 20 is connected to this port ENTER Continue ESC Back Up Select a COM port This screen tells you to type the number of the desired COM port 1 or 2 or H to select the Host Interface and a message prompting you to Check to be sure the TEF 20 is connected to this port The TEF does not necessarily need to be connected when you re simply installing the software Note If you intend on using parallel communications select Host Interface at this time You will be able to select parallel communications once the program is installed Press Enter to continue 2 3 Sound Lab TDS Install If you selected or 2 you will proceed immediately to Copy the demo files CY H WN Continue ESC Back Up Use the left amp right arrow keuz to highlight the HI base address as set bu the DIP switches on the HI interface board ENTER Continua 2 4 a screen with a message Copy the demo files Choose Y or N to continue We recom mend that you choose yes If you selected the H option a new screen will appear with the following message Use the left and right arrow keys to highlight the HI base address as set by
12. highpass filter A filter that passes frequencies above a certain frequency and attenuates frequencies below that same frequency A low cut filter Hz Abbreviation for hertz impulse response Sound pressure versus time measurement showing how a device responds to an impulse A potential versus time measurement showing how the potential of a system varies with time when stimulated with a zero width infinite amplitude pulse initial time delay gap Abbreviated ITD the time in milliseconds msec between the arrival of the direct sound at a listener and the arrival of the first significant reflection A reflection s significance is dependent upon its level in dB compared to surrounding scatter and its time interval It is the first total spectrum reflection containing substantial energy relative to the direct sound F 11 Sound Lab TDS Glossary all intensity sound sound energy flux in a specified direction at a point is the average rate of sound energy transmitted in the specified direction through a unit area normal to this direction at the point inverse square law rate of level change An attenuation of 6 dB for each doubling of distance from a source of sound Ldn noise measurement A 24 hour Leq except 10 dB is added to all levels measured between 10 00 PM and 7 00 AM to account for the need for more quiet during sleep hours Lden noise measurement A 24 hour Leq except 5 dB is added to all le
13. 0150 D o O To 0 oo bo O O j gg amp A D G O A A A DD a o wv o F amp F 9 0 B 4 QW 06 n o KK 6 A 98 i MN FILE TIM1 TDS FREQUENCY Hz Smoothing 0 027 Dist Hes 1 0 Freq Res 1130 0 Illustration 6 14 Pressing F4 function key enables a dialog box that allow precision incremental adjustments to the receive delay 6 20 jJ Sound Lab TDS Practice measurements When you press F4 a data dialog box will appear at the top of the display The present setting for the Receive Delayis highlighted and can be edited to several places from the keyboard Use the Left and Right arrow keys to move to the place value you want to edit You simply type in the delay that you want and then press Enterto have your selection entered into the parameters You can then re test and repeat the above procedure until the desired display is accomplished For most purposes adjustments by tenths or hundredths of a millisecond are effective The following series of illustrations shows the progression of adjustments to arrive at a precise receive delay Minor errors in the setting of the receive delay have virtually no effect on magnitude measurements However as we shall see phase measurements are extremely sensitive and the receive delay must be properly set For many devices a two way loudspeaker for example there is no one correct receive delay for phase measurements Unless the micropho
14. 10 Leal gaza mma qnod dun dun ad oper de ed ch dii rd qp m dea Lacu o nen n be ale 20 LL i D 30 k i f E E L 192 75 o p B n 2 a g D 57 37 H E 3 A t5 b TDS Delay 3D Start Delay 3D End Delay FILE SNCTOMLY ETC TIME milliseconds Start Freq 1782 0 Stop Freq 2218 0 Illustration 6 22 Classical RT6o numbers calculated by the TEF analyzer C l Sound Lab TDS Practice measurements HT amp O ALcons val Early Decay Time The Early Decay Time is a number that corresponds to perceived decay time _ To find the Early Decay Time put the left cursor on the direct sound at 50 48 gt Movethe right cursor until the dB down information box shows as close as possible to 10 dB 9 8 The RT60 information box at the top of the screen will now indicate the Early Decay Time RT60 of 0 58 seconds TDS File Heasure Parameters Display EDir ERev 0 4 dB Alcons 3 37 Cap HAOGNHITLDE er so ae n 192 75 o m ue a 6 66 54 E 5 B z E 2 FILE SNCTOHLY ETC TIME milliseconds Start Freq 1782 0 Stop Freq 2216 0 Illustration 6 23 Using the cursor to find the early decay time 6 33 6 34 TDS _ Sound Lab TDS Practice measurements RT60 ALcons ail Finding the ALcons To find the ALcons place the left and right cursors as for the Early Decay Time Look at the first 20 milliseconds after the direct sound for the presence of any significant reflectio
15. 2219 0 Illustration 6 21 Data cursors analyze and report RT60 and ALcons data 6 30 _ Sound Lab TDS Practice measurements RT6O ALcons mi Classical RT60 You can manipulate the cursors on the analyzer to accomplish a more classical RT60 value by manually placing the cursors on the display such that the left and right cursors span the longest and smoothest linear range possible This includes as much dynamic range as possible in the calculation To move the cursors manually you must select them and move them with the mouse or arrow keys gt Place the Rcursor to the right end ofthe linear range at 720 52 milliseconds gt Place the cursor to the starting point of the linear portion of the decay on the ETC at 192 75 milliseconds The reverberation time shown in the RT60 information box now reads 0 92 seconds See illustration on next page Note At any point when the RT60 cursors are active you can see the actual linear regression line by choosing the S ope button or pressing the Quick key O You can see an illustration of this on the next page 6 31 6 32 Sound Lab TS Practice measurements RTBO ALcons TDS File Measure Parameters Displau Input RT6eO 0 92 Sec EDir ERHeu 2 5 dB ALcons 4 63 dE down 34 92 ro ry acp er ees ee a ey 0 i T j TEF 5 20 40 TE i a T 30 i 30 hoa i w i 8 20 pa ni a gt T 5 i0 Fus g TAI 50 O MA A E Ad i l 60
16. Auto Scaling Alt House on Alt Beep on Adjust Colors Illustration 4 23 Display Time Response submenu Top of Scale The Top of Scale value in dB determines the value that will be displayed at the top of the vertical scale This data entry value will be rounded to the nearest 10 dB increment Sound Lab TDS Display Menu mi Bottom of Scale The Bottom of Scale value in dB determines the value that will be displayed at the bottom of the vertical scale This data entry value will be rounded to the nearest 10 dB increment Auto Scaling Toggle Auto Scaling on or off If Auto Scaling is On the software will automatically scale the data to display the full magnitude range of the measurement The highest data value is placed in the top 10 dB of the graph and the scale annotation is adjusted accordingly The new Top of Scale and Bottom of Scales will be updated when the data is redisplayed Manually entering a value for Top of Scale or Bottom of Scale automatically toggles Auto Scaling Off We recommend that Auto Scaling be left on for most measurement tasks If Auto Scaling is off and all the data is out of the selected range you will not see any data on the screen Auto Scaling can be toggled off if you don t want the graph s Top of Scale value to change with data level from test to test This is a requirement if you are going to use Overlay to create a family of curves on the screen resulting from sev
17. Performing measurements Time and Frequency Response mil 8 At this point you may run the test by selecting Do Time Test under the Measure menu or by pressing function key F5 You will see the display on the screen and be able to examine it AMPLITUDE dB TIHE Hilli Secs Illustration 5 2 ETC Display of a Time Response Test 9 Refine the time scale if the first reading is too coarse for clarity See Appendix A How TEF works for more information on resolutions 10 From the Display menu select Time Response to experiment with other ways to display the data 11 12 13 Sound Lab TDS Performing measurements Time and Frequency Hesponse mi Printing the display If you wish you can print the graph From the File menu choose Prinier Settings Try using the default settings With your printer turned on select Print to print the display Saving the settings You can save any settings you used in testing and load them later by selecting Configuration and entering a name in the dialog box which appears Saving the data To save the test data select Save As from the File menu Select Clear All to set up the dialog box for your information Enter File Name and any other information you desire Select Binary under Format select Save and close the dialog box to continue with your next measurement 0 5 0 6 Sound Lab TDS Performing measurements Time and Frequency Hesponse Performing a
18. a device specification frequency response is the range of frequencies that an audio device will reproduce at an equal level within a tolerance such as 3 dB frequency span That region of frequencies from the lowest to the highest over which the TEF sweeps for analysis and display frequencies of interest see frequency span FTC Frequency Time Curve A graph of time and frequency with magnitude displayed in the form of dB contour lines full scale time tThe time span shown on the right end of the screen of an ETC measurement It is dependent on the frequency span of the sweep and number of samples fundamental The lowest frequency in a complex periodic wave gain an increase in power The ratio expressed in decibels between output power and input power of a system see decibel harmonic An overtone whose frequency is a whole number multiple of the fundamental frequency j 3 Q p a D gt 5 Glossary ull hertz The unit of frequency representing cycles per second heterodyning Mixing two frequencies together in order to produce two other frequencies equal to the sum and difference of the first two For example heterodyning a 100 kHz and a 10 kHz signal will produce a 110 kHz sum frequency and a 90 kHz difference frequency signal In TEF it means changing the frequency of the incoming signal signal being analyzed so that it is at the I F filter s center frequency
19. band sound pressure levels versus frequency in eight octave bands The lowest NC contour not exceeded by the curve becomes the NC value 4 11 Sound Lab TDS Measure Menu mi Do STI Test Speech Transmission Index Do RASTI Test RApid Speech Transmission Index performs STI and the faster RASTD tests by running several time response tests plus an NC measurement and then processing the data to yield an overall speech intelligibility prediction The resulting data is displayed on the screen in a graph or table e STI makes modulation transfer function MTF measurements in the seven octaves from 125 Hz to 8 kHz e RASTI is a shortened version of the STI proce dure measuring the MTF at the 500 Hz and 2 kHz octaves When you choose Do S11 Test Do RASTI Test and Do 5D Test a Save as sub menu appears because you must name the test before it begins File Name ALTAROOL ETC Title ETC Taken To Show Feedback Through Altar Mic Usar Hane LJS JA B Date O7 28 1993 09 15 33 Location Coalbush Church South Bend TH Description Line 1 1 Second ETC Center At 2kHz Line a PCE 160 On Altar Used ns Pick Up Mic Farnat Binary Save Illustration 4 12 Save as sub menu Bos You can set the parameters to do a noiseless test and edit in noise later from a stored NC file or the NC table in the Display menu 4 12 Sound Lab TDS Measure Menu il Do 3D Test performs from 2 to 100 individual TDS measurements each offset i
20. i Y 5 3 ole entered T Table 4 1 shows the interdependent parameter relationsbips for the Time Response test A ME EIEIEIEIEIEI 4 19 4 20 Sound Lab TDS Parameters Menu TDS parameters Frequency Response The interdependent parameters for Frequency Response TDS tests are start frequency stop frequency sweep time sweep rate resolutions receive delay bandwidth and number of samples Entry of one of these TDS parameters may change the value of other TDS parameters to keep the complete parameter set valid Table 4 2 shows the TDS dependent parameter relationships Parameters Time Response LETC Frequency Response TDS 3 Start Frequency 100 0 Hz Stop Frequency 10000 0 Hz Sweep Tine 1 0 s Sueep Hate 10312 5 Hz s Resolution Frequency 101 6 Hz Distance 11 1 ft Tine 9 2473 ns Best Frequency Hesolution On Receive Delay 0 6125 ns ore Hz Number of Samples gia Illustration 4 15 The parameters for the Frequency Response test Start Frequency TDS the starting frequency of the sweep Stop Frequency TDS the ending frequency of the sweep SweepTime TDS theduration in seconds ofa TEF sweep Sweep rate TDS the rate in Hz second of a TEF sweep Sound Lab TDS Parameters Menu Resolution TDS the smallest increment that can be correctly discerned in a parameter you have chosen Frequency the smallest increment of fre quency that you will be able to resolve or
21. in the measurement 6 24 ARPLITUDE iB Sound Lab TDS Practice measurements FREQUENCY Hz Dist Res ee rea FILE TIMS TDS anl 2 PHARF Nea amp B 8 Sound Lab TDS Practice measurements T60 ALcons mi Making ALcons and HT60 measurements For the purposes of this exercise we are assuming the user to be a contractor or designer with a fundamental understanding of navigation in Sound Lab TDS software The task is to calculate ALcons and RT60 data out of a valid ETC measurement in order to e meet a bid specification e verify the reverberation time of the room e determine if the decay is appropriate for the functions that are going to occur in this environ ment Sound Lab TDS performs two common acoustic calculations useful to the designer consultant and contractor the RT60 and ALcons Both are calculated from data collected in a Time Response ETC measurement It follows then that to yield valid RT60 and ALcons numbers you need to have appropriate ETC data Terms to know To have a working knowledge of the exercise to follow here are terms to know ALcons The measured percentage of Articulation Loss of Consonants by a listener With TEF methods articulation scores are measured as percent of articulation loss of consonants in speech A ALcons of 0 indicates perfect clarity and intelligibility with no loss of consonant understanding while 1096 and beyond is growing
22. listener 3 the signal delay between two transducers either microphones or loudspeakers 4 Any other signal delay in a sound system that exceeds that normally expected from a minimum delay system Sound Lab TDS Glossary mi diffraction The bending of a wave front around an obstacle in the sound field see reflection diffuse field Sound field in which the sound pressure level is the same everywhere and the flow of energy is equally probable in all directions diffuser A device to enhance the spreading of sound for even distribution of sound in an environment diffusion The spreading of sound reflections to achieve an even distribution of sound in an environment direct sound Sound that has traveled from the sound source to the observer and has encountered no reflecting surfaces see Q directivity factor Q The ratio of the sound pressure squared radiated directly ahead of a sound source to that sound pressure squared radiated in all directions discrete sound arrivals Sound arrivals at the microphone or listening position that are separated in time domain The X axis or independent variable in a measurement see time domain frequency domain doppler effect The change in the observed frequency of a wave caused by a change in the velocity of the sound source An example of the doppler effect is the difference perceived in pitch of a car horn as it approaches As it approaches it ap
23. squares of the instantaneous values of a varying quantity In periodic variation the mean is taken over one period Sabin a unit of absorption equal to the absorption of 1 square foot of surface which istotally sound absorbent Schroeder integration of reverberation An integration of reverberant data in which the last energy is integrated first and the initial arrival is integrated last all ofwhich is normalized by thetotal The integration simulates the effect of taking many time measurements and averaging them together signal delay commonly but inaccurately called time delay The difference in arrival times between two signals A signal delay is also a device for delaying a signal Sound Lab TDS Glossary mi signal to noise ratio The ratio in decibels between signal and noise An audio component with a high signal to noise ratio has little background noise accompanying the signal a component with a low signal to noise ratio is noisy sine wave A wave following the equation y sin x where x is degrees and y is voltage or sound pressure level The waveform of a single frequency sone a unit of loudness It is defined as the loudness of a 1000 cycle tone 40 dB above threshold A millisone is one thousandth of a sone and is often called the loudness unit sound Energy that is transmitted by pressure waves in air or other materials and is the objective cause of the sensation of hearing Longitudinal vi
24. strongly influenced by noise or excessive reverberation see AL attenuate attenuation The lessening of the sound signal level due to divergence absorption reflection refraction diffraction etc expressed in decibels The decrease in sound level with distance in the direction of propagation The reduction of the level of a speaker band pass filter A filter that passes a specified frequency band while all frequencies above and below this band are attenuated see bandwidth center frequency bandwidth The difference between the values of the frequencies where the filter s response has fallen by 3 dB In TEF the bandwidth of the tracking filter can be preset The wider the bandwidth the greater the time window see time window band pass filter center frequency F 4 Sound Lab TDS Glossary TI comb filter comb filter effect A sequence of evenly spaced peaks or dips in the frequency response plot when viewed on linear scale caused by two or more identical signals which combine at near equal amplitudes but at slightly different time intervals complex wave A wave with more than one frequency component compression The portion of a sound wave in which molecules are pushed together forming a region with higher than normal atmospheric pressure Also in signal processing the reduction in dynamic range caused by a compressor coverage the distribution of direct sound levels in a listenin
25. 2 0o a Sr mH amp Re Q D gt S A SER 9 9 e e T GX es A Display parameters for Magnitude and Phase display Illustration 4 29 4 50 3 z a r Q gt E O Y Display Menu mi Display options Frequency Response Nyquist The options for the Nyquist data display are Top of Scale Bottom of Scale Auto Scaling Graph and Display Rotation and Octave smoothing Time Response Frequency Response TDS gt Nyquist Magnitude Top of Scale Bottom of scale Auto Scaling Phase Top of Scale Botton of Scale Auto Scaling Hrap T st seein rie ens eM is d tad xen LUE TE See um ES pine he E T T m dn road nem relies A a Illustration 4 30 Nyquist display parameters 4 51 4 52 Sound Lab TDS Display Menu mil The Nyquist display plots magnitude versus phase angle It can be thought of as the tip of a vector that is changing in both length and angle as the frequency sweeps The length of the vector is proportional to the magnitude of the data and the angle of the vector represents the phase of the data When the data cursor F2 is used a readout appears in the lower left corner of the display showing the frequency phase magnitude and the real and imaginary values Graph Toggle to choose dB or Linear data in the Nyquist display Display Rotation Data entry for the degrees of counter clockwise rotation you want in the Nyquist display starting from
26. 20 index 4 Sound Lab TDS Index nil GD 431 TDS 4 21 Best TDS 4 21 response F 10 Span B 9 F 10 ETC 4 17 Start F 26 GD 4 30 ETC 4 16 TDS 4 20 Stop F 26 GD 4 30 ETC 4 16 TDS 4 20 Frequency Response TDS Parameters 4 20 Ns Bottom of Scale 4 51 Display Heyser Spiral 4 42 Magnitude 4 42 Nyquist 4 42 Phase 4 42 Graph Nyquist 4 51 Nyquist 4 51 Test 5 6 E Top of Scale 4 51 Front to Back 3D 4 56 FIC F 10 full scale time F 10 function keys 3 7 gt fundamental F 10 NP G Gain definition F 10 Go to command 3 8 4 9 Graph Nyquist 4 51 Size 4 8 T Hamming window 4 18 harmonic F 10 Help from Techron 1 5 hertz F 11 heterodyning F 11 Heyser Spiral Frequency Response 4 53 Time Response 4 42 4 46 Heyser spiral display 4 53 HI base address 2 4 HI communication 4 82 highpass filter F 11 Horizontal Scale 3D Waterfall 4 55 Frequency Response 4 48 4 49 4 50 Linear Log 4 48 Host Interface 2 3 Hz Abbreviation F 11 impulse response F 11 input hardware setting 6 5 Input menu 4 73 Calibration 4 76 Distance Unit 4 80 Propagation Speed 4 79 Qn Q c 3 Q m Qi mo g 0 naex Reference Unit 4 78 Volts per Reference Unit 4 78 Zero dB Reference Value 4 78 Communication 4 81 Baud Rate 4 81 HI Base 4 81 Port 4 81 Settings 4 74 Channel 4 74 Input 4 74 Loopback 4 74 Installing 2 1 Integration Time Noise Test 4 27 interrelated parameters 4 20 B 8 J j
27. Daeg pyc ence ai iSite ag gee um dp VERE TRY ba SPUD lios pl Ee BH eae pecie te beeen ame E ars in de kd Vi az A TM AM HN intei ETE ac 10 i i i iM 1E Illu stration 5 6 63 125 250 500 1000 2000 4000 9000 NC curve Frequency Hz The single number NC rating assigned by NC is the highest curve that is not exceeded by data in any octave band This implies that noise in a single octave determines the NC rating since the effects of the different bands are not additive The lower boundary of the family of NC curves NC15 represents the point at which noise is perceived by most people to be objectionable The highest curve NC70 represents noise in which people can communicate only by shouting in each other s ears The curves are spaced 5 dB apart through the mid frequencies because the average listener will not react to a change in the noise that is less than 5 dB even though smaller changes can be detected The shape of the curves accounts for low frequency noise being less annoying or noticeable than high frequency noise Sound Lab TDS Performing measurements STI RASTI niill Introduction to STI The speech transmission index STD is an evaluation of how well the amplitude modulation patterns of speech are preserved when passed from their source to a listener STI and RASTI measurements Sound Lab TDS makes two types of speech intelligibility measurements based on the Speech Transmission Index STD
28. Doing a Time Response Test ETC eese 6 4 Equipment arrangement s cian R rite eed aka tase 6 4 Sel the input para meteis enormen dio stos 6 5 Calibri nne the display ii na Ea A cette ctc ergo A 6 6 Setting the parameters for the Time Response test ssss 6 7 Setting up the screen display ic A s usce 6 8 lil Sound Lab Contents il Running the Time Response test cccccccescseeeeeeeeeeeeeeseeenaeeseseacesenees 6 9 The power of he data CUFSOF aieea eet iere 6 10 Using the cursor to examine the data seorsan 6 11 Fimpar eNe abies elec occ san erbe reet O pae 6 12 Doing a Frequency Response Test TDS ooooocccnccononcncnoninannanonannnannnnonos 6 14 Setting the parameters for the Frequency Response Test 6 15 Setting thre soren display A nter rentre Ree 6 17 R D spice e H 6 18 Adjusting the receive delay to tune in to the phase 6 19 Making 96ALcons and RT60 measurements 6 25 Tenm tool 6 25 o E IAG cores oe corre cucu eaters ee eet 6 26 EEO ETE DETAI r o ee eL LESE 6 27 YA e TN NITE wees 6 28 Power Onte C SO Booster tale de 6 28 Additional information e etenin ESSE uis ise E OA 6 30 las ever URS 6 31 EM a all 6 33 Exige di A O e OO UD d 6 34 Appendix A Basics of sound A 1 AMES a m aar sm ecce tect m NS AL MD ttn dd A 1 Whistrati mtA 3 Three cycles Of A Wave ertet nri A 3 hasactesisties Of sound WAVES ou n i E aga c
29. Glossary il arrival of the direct sound and the onset of reverberation Usually the longer the pre delay the greater the perceived room size propagation The travel of sound waves through a medium pure waveform A waveform of a single frequency asine wave A puretone is the perceived sound of such a wave Q The ratio of the sound pressure squared at a distance r in front of a source to the sound pressure squared averaged over all directions A source that radiates equally in all directions spherical source has a directivity factor Q of 1 A hemispherical source has Q of 2 a source in a corner which radiates into one quarter of a sphere has a Q of 4 etc RASTI Rapid Speech Transmission Index expressed ina decimal range of 0 2 for bad to 1 00 for Excellent This method of evaluating speech intelligibility is based upon the method of the Speech Transmission Index STD Perfect transmission of speech implies that the speech envelope at the listener s position replicates the speech envelope at the speaker s mouth Speech intelligibility can be quantified in terms of the changes in the speech envelope as a result of noise and reverberation in the room In TEF an equivalent of the RASTI method is achieved by testing only at the 500 Hz and 2 kHz octaves Sound Lab TDS Glossary mi RT Reverberation time The time in seconds for the reverberant sound field to decay 60 dB after the soun
30. Handbook for Sound Engineers The New Audio Cyclopedia Carmel Indiana Howard W Sams 1991 Bruce Bartlett Introduction to Professional Recording Techniques Carmel Indiana Howard W Sams 1987 Leo L Beranek Acoustical Measurements Rev ed Cambridge Massachusetts Published for the Acoustical Society of America by the American Institute of Physics 1988 Lothar Cremer Helmut A Miller Theodore J Schultz Principles Applications of Room Acoustics Essex England Applied Science Publishers Ltd 1978 Malcom J Crocker Noise Control New York New York Van Nostrand Reinhold Co 1982 Don Davis and Carolyn Davis Sound System Engineering Indianapolis Indiana Howard W Sams 1989 Sound Lab Bibliography nil J R Hassail and K Zaveri Acoustic Noise Measurements Naerom Denmark K Larsen amp Sons A S 1979 Richard C Heyser Time Delay Spectrometry An Anthology of the Works of Richard C Heyser on Measurement Analysis and Perception New York New York Audio Engineering Society Inc 1988 Peter Mapp The Audio System Designer Technical Reference by Klark Teknik Plc Harry B Miller Acoustical Measurements Volume 16 Methods and Instrumentation Stroudsburg Pennsylvania Hutchinson Ross Publishing Co 1982 Michael Rettinger Acoustic Design amp Noise Control Volume 1 New York New York Chemical Publishing Co Inc 1977 Earl D Schubert Psychological Acoustics V
31. Illustration C 2 is a difference showing good repeatability There is very little difference anywhere in the display e a T Le Li a m amp 5 l m araar amp 10 e M 15 PA 20 J n LY a el N MODE DIFF i TIME MilliSecs Illustration C 2 A difference witb good repeatability Another way to check for repeatability is to turn on overlay mode and make several measurements The data from each of the measurements should lie right on top of each other C 3 AMPLITUDE dB 100 1000 2000 Illustration C 3 Two signals being measured at once C 4 3000 j Sound Lab TDS Data Interpretation il Some things to watch for The are some common errors which can easily creep into our measurements If we can learn to recognize their telltale signs we will be able to immediately spot them and take action to eliminate them Whenever two similar signals arrive at our measuring microphone with nearly the same level but at slightly different times they will interfere with each other and cause anomalies in the measured response This will be the situation when we have set too large a time window and a reflection is measured along with the signal we are really interested in Illustration C 3 shows the telltale signature of two signals being measured at once Notic
32. Menu ail Display options Frequency Hesponse Magnitude The parameters that affect the Frequency Response Magnitude display are Top of Scale Bottom of Scale Auto Scaling Horizontal Scale and Octave Smoothing Display E 3 E TUM LOIS NODE Top of Scale Botton of Scale Auto Scaling Hrap Nyquist Top of Scale Bottom of Scale Aute Scaling Graph Dian lan dorados eee Hater gine eames ee SERO EE Pon pend Horizontal Scale o tee PES ri WEE s at ax a s rer v 2 PEREPERE a ST inicio Alt Close Alt Undo Illustration 4 28 Parameters for Frequency response magnitude display Octave smoothing Enter a percentage value for desired amount of octave smoothing to be performed on the data to be displayed The value may be entered as a fraction but it will be displayed in the menu as a percent 4 49 3 S z a y a S 8 D m AS Q S S8 x Y gone ue T gt OQ d Se se ues i px 3 2 m Y oe Bi a S c Ye gt S d IT p Q S S S o p VS Q a O A E oto 9 gt uU Q v O s e S Q S S wy De ao E S S SOS S p S SS i ce gt FJARA o ZAS wv xcu A e C moe os Ss E p S S m 2 z y T o Sd eg 2 B S Q E DR Beers B BS La QJ t A S IO ou a y E p u rm Ye TRL T e EE o po LA Beh a2 1I E EN EE ae cole ef S super a a 2 Poe 43 f E S 4H oe won Q D o Ww SO Ti verfo Og c o 3S U ne wo 8 S Ones ss 2 co Z3 Bs Sd S c t 209 Og Eo O R
33. Parameter label Value Comments EICZ Save Rate k 47 Number of Samples 512 Start Frequency gt 141 0 Stop Frequency 358 0 Sweep Time 2 01 Sweep Rate 1496 0 Bandwidth 0 0 Receive Delay 0 0000 Output Level 9 1014 Data format ASCII Data type SINGLE Data count 511 Data o 9 944027e 6 2 611652e 5 1 224643e 5 2 667577e 5 7 479048e 6 1 317536e 5 ETC3 ETC4 ETC5 ETC6 ETC E 24 Sound tab TRS File formats ani 3D file format The 3D master file header The 3D master file with extension 3D contains information that is common to all individual tests in the 3D set such as the test title date and location description of the test and number of measurements or TDS files in the measurement The lines for Third Axis contain labeling and value information for Start time Stoptime and Time step The Max Y Data value is the largest data value in all TDS files The Min Y Data is the minimum data value in all TDS files The associated data for each of the measurements in the set accompanies the file with the same name plus the extensions 001 002 003 etc See TDS ASCII files E 10 for information on individual TDS files s TEST 5D temere ee eem mene eene ee Ei et ee eit ors lo i ge ura LEAB E d 2 1 91 1801 6 locations OOO Coal Church i
34. STI RASTI CSTI 3D Test lt 3D gt Averaging Several of the Sound i 4 Lab test parameters Tine Response ETC B for the Time Re Frequency Response TDS gt sponse ETO test are interdependent entry of one param eter may change the Output Pink Noise White Noise Sine Wave Tone Frequency llustration 4 13 The parameters menu value of another To keep the complete parameter set valid Sound Labforces an entered parameter to its nearest valid value or issues a message to help you set valid parameters If you receive a message adjusting another parameter may allow you to enter a parameter in the range you desire Sound Lab rounds all entered parameters to the nearest valid value For example if you enter a time span of 100 seconds the actual value entered by Sound Lab would be 998 1652 seconds This slight change results from the digital implementation of the sweep Sound Lab allows only certain sweep rates to be selected 4 15 4 16 Sound Lab TDS Parameters Menu mi Time Response ETC Parameters The interdependent ETC parameters are Start frequency stop frequency center frequency frequency span sweep time receive delay time span number of samplesand window Entry of one of these parameters may change the value of other ETC parameters to keep the complete parameter set valid Table 4 1 shows the ETC interdependent parameters relationships Parameters line Respons
35. TDS How TEF works il frequency resolution 1kHz The fine detail is still there in reality we just can t see it Trade off between time and frequency Because time and frequency resolutions are reciprocals of each other we can trade away resolution in one domain for resolution in the other However there is always an inverse trade off when converting from one domain to another this means that as the resolution in one domain goes to infinity the resolution in the other domain must approach zero The product of resolution in time and resolution in frequency will at best equal one With TEF it is always one For example if we wish to measure a loudspeaker with a resolution in frequency of 20 Hz then our resolution in time is 1 20 or 05 seconds At the speed of sound 05 seconds is equivalent to 56 5 feet Reflections from objects within that distance will be included in our measurement yielding false results If we now reduce our resolution in frequency to 500 Hz our resolution in time increases to 1 500 or 002 s conds This corresponds to a distance resolution of 2 26 feet and true anechoic measurements are easily performed in smaller spaces Note that the limits on frequency resolution are not unique to TDS as TDS measurements perform at the theoretical limits of time frequency resolution The limits are a direct consequence of frequency resolution being the inverse of time resolution and applies to all measurement s
36. You must choose ir Measure from the dialog box Measure i to start the test Hlustration 5 11 Sound Lab will continue the STI RASTI test and first mea sure any noise in eight octave bands When the noise tests are complete STI then per forms seven ETC tests two for RASTD When all of the ETCs are complete the soft ware then calculates the over all STI and displays the results in the active window in a table or graph depending on your choice made under STRASTI in the Display sub menu Save As dialog box allowing you to name tbe test and start the STI sweeps 5 20 Sound Lab TDS Performing measurements STI HASTI mil Since calibration and equalization are complete to measure at other listener positions you can simply initiate the STRASTI sweeps from under the Measure menu in your usual manner The level calibration and equalization procedure should be performed every time a different loudspeaker or microphone is used and any time the gain controls are altered in the measure ment setup Driving the system directly If you do not use the talker speaker arrangement but prefer to go through the house system directly the levels again should be set the same as for a person speaking In this arrangement of course you do not perform the calibration procedures Make certain that the reinforcement system level is predominant either by listening or by making a Time Response test and checking the signal strength
37. along with common errors that can creep into measurements 1 3 1 4 Sound Lab TDS Introduction Appendix D On screen messages Appendix E File structures Appendix F Glossary of terms Appendix G TEF resolution V Ill C Sound Lab TDS Introduction ud Customer support All Techron products are backed by a customer support system If you need assistance beyond that provided in the manual follow these steps e Try to duplicate the problem keystroke by keystroke to see exactly what was done e Have the date and version number of software available This information is displayed in the File About sub menu e Have the date and version number of the manual available found on the front cover page e Be at the TEF analyzer and call customer support Customer support for Techron hardware and software can be reached by dialing 800 833 8575 North America 219 294 8295 Outside North America 219 294 8302 FAX Techron Customer Support takes calls daily from 8 00 AM to 5 00 pm Eastern Standard Time Before 8 00 or after 5 00 you may leave a recorded message via voice mail or send a message via FAX The automated TEF FAX Information System has an index of various topics related to the TEF analyzers and software that you can request to have transmitted to your FAX machine U Section 2 Sound E ID a Sound Lab Install program Assumed is a minimal knowledge of DOS and that you know how to
38. amplitude reading you get in a display is always accurate in a dB relative sense If you need to know the absolute amplitude of a measurement relative to 0 dB SPL the numbers will be incorrect unless you have first calibrated the instrument To display data Sound Lab software uses reference units volts per reference unit propagation speed distance units and a 0 dB reference Without this information Sound Lab would show data only in terms of volts and seconds and not the more familiar units of sound pressure level and feet Settings Calibration Reference Unit Pascal Uolts Per Reference Unit 0 00226 Zero dB Reference Value 0 00002 Propagation Speed 1130 0 Distance Unit feet Illustration 4 50 Calibration sub menu Sound Lab TDS Input Menu To enter these units choose Input and select Calibration The first time you use the software try these values Reference UMitdii nane pascal Volts per reference unit 00226 Typically B amp K 4007 microphones are 00226 volts pascal See your microphone data sheet under the specification Sensitivity Zero dB Reference Value 0 000020 pascal this corresponds to 0 dB SPL Propagation speed 1130 feet second for sound traveling in air at 209C Distance Unit FON E Set to Feet this correlates with the propagation speed The propagation speed will change as you change the
39. are five types of frequency response displays which you can select under the item called Frequency Response Phase Phase vs frequency orphase response Magnitude Magnitude vs frequency or the familiar frequency response Magnitude and Phase Displays both the frequency response and phase response on the same screen Nyquist A rotating vector showing magnitude vs phase angle on a polar plot Heyser Spiral Shows the complete system response in one view a three dimensional curve in which the three projections are the polar real and imaginary planes Sound Lab TDS Display Menu mm 3D Waterfall Displays frequency response vs time in successive time slices NC Noise Criteria Noise contour graph showing octave band sound pressure levels vs frequency in eight octave bands STI Speech Transmission Index A measure of the intelligibility of a sound system Display Type Magnitude a Illustration 4 22 Time response ETC sub menu 4 44 Sound Lab DS Display Menu mu Display options Time Hesponse magnitude When you select Time Response Display type a submenu allows you to choose two different ways to view the measurement data Magnitude or Heyser Spiral The parameters which can be set for the Time Response Magnitude display are Top of Scale Bottom of Scale Auto Scaling bisplas Time Response ETEY Magnitude Magnitude Top of Scale 60 dB Bottom of Scale 10 dE
40. button See sche matic in analyzer user manual Pulse trigger This option was designed specifically to be used with an accessory turntable connected to the TEF through the external trigger connector For specific turn table details refer to the instructions from the manufacturer Outline Outline snc Via Leonardo da Vinci 56 25020 Flero BS Italy 030 3581341 FAX 030 3580431 Sound Lab TDS Parameters Menu m 3D Curve Spacing C Ch und Resulting NC No change change gt Change Start Receive Delay entered End Receive Delay NC u e ne T C Receive Delay Step C NC NC n Table 4 4 This table shows 3D curve spacing interaction For interaction among other parameters see previous tables 4 35 4 36 Sound Lab TDS Parameters Menu mil Parameters for Averaging Sound Laballows you to perform a vector or magnitude average of two to 999 frequency or time measurements Paraneters Time Response ETC Frequency Response CTDS gt NC gt Noise Test STI HOSTI STI gt 3d Test 3D Measurement Type Frequency Averaging Type Magnitude Number of Sweeps 200 Pause between Sweeps Os Test Sequencing Automatic Attese ATE Undo Illustration 4 19 Parameters for Averaging menu and sub menu Measurement type Avg Toggles between Frequency and Time Choose the measurement type you wish to average Averaging Type Avg Toggl
41. connection from output to input To verify that the TEF is working turn on Loopback and perform a frequency response test The resulting display shows the internal frequency response of the TEF Sound Lab TDS Input Menu nnil Preamp Gain Preamp Gain A To set the gain of the microphone preamp for Channel A elect Preamp Gain A and enter the number of dB of gain you wish the microphone preamp to have A typical value is 40 to 60 dB Use the same method to set Preamp Gain B Sound Lab accepts gain changes in 4 dB increments from 0 to 60 dB 0 4 8 etc When setting the input gain use as much gain as possible in the preamp Gust like in a sound system put the gain up front Once you start measuring adjust the gain up or down until it is as high as possible without getting an overload indication from the software If the overload ovld LED on the TEF lights during the measurement either the Preamp Gain or the system output level is too high A good practice is to set the output level of the amp to obtain a test signal level of about 70 dB SPL conversation level Then if the overload light comes on reduce the microphone preamp gain Note It is not a good practice to set the output level with the output level knob on the TEF since some tests require this knob to be in the calibrated position to get calibrated results 4 75 4 76 Sound Lab TDS Input Menu Calibration sub menu Calibrating the display The
42. curve is to smooth it out and minimize peaks and valleys If we wish to increase frequency resolution to its highest possibility we would use a receiver of infinite bandpass and infinite time window and a transmitter of pure sine wave signals The receiver could then at any time during the measurement hear any single frequency but would have zero time information resolution time The amount of detail you are able to resolve or see in the time domain Increasing the time resolution making the time window smaller will have the effect of decreasing the space window ellipsoid This will decrease the frequency resolution since the units of time and frequency are reciprocals of each other In making TEF measurements time and frequency resolutions are adjusted by selecting appropriate combinations of sweep rate and filter bandwidth This limits us to those frequencies that develop at least one wavelength within that time span resonance A maximum response to an applied frequency a peak in the frequency response Resonance exists between a body or system and an applied force if any small change in frequency of applied force causes a decrease in amplitude of the responding body eu Naz Sound Lab TDS Glossary tl resonance frequency The frequency at which resonance occurs Of a traveling wave resonance frequency is the change in amplitude as the frequency of the wave approaches or coincides with a natural frequency of
43. description Wrap When Wrap is toggled on the phase curve will wrap or start over at the top of the scale as frequency progresses The top of the phase graph will be 180 degrees and the bottom will be 180 degrees With Wrap off the phase curve will be continuous without any sudden 360 degree phase jumps or transitions If you edit the Top of Scale or Bottom of Scale the Wrap feature turns off Graph Toggle to choose dB or Linear data in the Nyquist display Display Rotation Data entry for the degrees of counter clockwise rotation you want in the Nyquist display starting from zero degrees Horizontal Scale Choose a Linearor Log display to set the horizontal frequency scale in frequency response displays Octave smoothing Enter a percentage value for amount of octave smoothing to be performed on the data in a magnitude and b magnitude and phase displays The value may be entered as a fraction but it will be displayed in the menu as a percent Sound Lab TDS Display Menu mil Perspective 3D Toggles between Left and Right views of the display Curve Order 3D Toggles between Front to Back and Back to Front describing the placement on the graph of the first curve measured The first curve is the one that is measured at the time set by Start Receive Delay Front to Back 3D The first curve measured curve 001 is placed in the front of the graph Back to Front 3D The first curve measure
44. diffusors to one or both of the offending walls Putting the material in patches rather than all together promotes an even distribution diffusion of sound in the room Heverberation Sound reflects not just once but many times from all the surfaces in the room These sonic reflections sustain the sound of the instrument in the room for a short time even after the sound source is stopped This phenomenon is called reverberation the persistence of sound in a room after the original sound has ceased For example reverberation is the sound you hear just after you shout in an empty gymnasium The sound of your shout persists in the room and gradually dies away decays In physical terms reverberation is a series of multiple echoes decreasing in intensity with time so closely spaced in time as to merge into a single continuous sound eventually being completely absorbed by the inner surfaces of a room Echoes increase in number as they decay Illustration A 8 shows reverberation as a decay in time of room reflections Note that reverberation is a continuous fade out of sound while an echo is a discrete repetition of a sound A 10 Sound Lab TDS Basics of Sound id Direct sound L A ToS Measure Parameters Disolmw Input AMPLI TUGE HB Illustration A 8 Reverberation A Reverberation formation B Amplitude vs time of direct sound early reflections and reverberation Sound Lab TDS Basics of Sound Heverbera
45. dimensions of the room its length width and height The formula for the most basic room mode resonance frequencies is f N x 565 D where f resonance frequency in Hz N 1 2 3 D room dimension in feet For example a room 12 feet long will have room modes at 47 Hz 94 Hz and so on Those frequencies or notes will be over emphasized in the music unless there is sufficient bass trapping in the room to dissipate them Other frequencies will be reinforced by other room dimensions If the height width and length of the room are identical the same modal frequencies will be reinforced in all three dimensions greatly emphasizing certain low frequencies On the other hand if the dimensions are not multiples of each other the modes will be different for each dimension Then each room mode will be reinforced in only one dimension and there will be a more even distribution of resonance frequencies A 13 Sound Lab TDS How TEF works nil hs Appendix B How TEF measurements work The TEF analyzer generates a sine wave frequency sweep which is played through a sound system and returned to the TEF The change in frequency of the sweep islinear with time The microphone signal is fed through a filter that tracks the sweep The tracking filter isin sync with the generated frequency sweep however it is offset in time to compensate for the propagation delay of sound traveling from speaker to microphone By varying the b
46. interval between any two frequencies where the upper frequency is twice the lower frequency octave the interval between any two tones whose frequency ratio is 2 1 offset time offset see receive delay Sound Lab TDS Glossary mu off axis Not directly in front of a microphone o loudspeaker E off axis coloration In a microphone the deviation from the on axis frequency response that sometimes occurs at angles off the axis of the microphone The coloration of sound alteration of tone quality for sounds arriving off axis to the microphone PFC Phase Response Phase frequency curve Phase versus frequency display peak On a graph of a sound wave or signal the highest point in the waveform The point of greatest voltage or sound pressure in a cycle peak amplitude On a graph of a sound wave the sound pressure ef the waveform peak On a graph of an electrical signal the voltage of the waveform peak period The time between the peak of one wave and the peak ofthe next The time between corresponding points on successive waves Period is the inverse of frequency phase Phase is the measure of progression of a periodic wave Phase identifies the position at any instant which a periodic wave occupies in its cycle Phase describes the progress of a waveform in time relative to some starting point If amplitude is plotted perpendicular to a time axis phase may be represented as a position along the time axi
47. kHz octave band contains approximately 1 3 of all intelligibility in speech Since we are examining speech these settings will center the information around 2 kHz a typical starting point for the first sweep you would do The time span of approximately one second was estimated by testing the room with a simple handclap and listening to how long it took the sound to decay Power of the cursor Sound Lab TDS has powerful cursors you can activate that automatically analyze and report RT60 and ALcons data Make the cursor active by pressing Shift F2 You will now see the following new information on the screen The smooth line above the original data is an integration of the time response data which smooths the decay curve Schroeder curve e Three cursors L D and R across the bottom of the display each with accompanying informa tion The Zand R cursors represent the left and right points of the reverberant field that will be used for determining the early decay time ML J A Sound Lab TDS Practice measurements O ALcons iil The third cursor labeled D sets the division between early direct sound and late reverber ant field energy Sound Lab TDS software uses this information to compute the Direct to Reverberant Energy Ratio e Cursor buttons at the bottom of the display Slope displays the line which best fits the data between the left and right cursors Linear regression line TDS
48. menus and sub menus a single button Mouse the Arrow keys and Quick keys Mouse You must have installed the device driver that controls the mouse to be able to use it in Sound Lab TDS If you do not have a mouse driver installed see your mouse manual for installation procedures Sound Lab uses the left button of the mouse to select items and move the cursors in displays Arrow keys The Arrow keys are a c group of four keys with imprinted CI name direction arrows Press the Left and Right Arrow keys to navigate along the Dike Ss main menu bar displaying each menu Illustration 3 2 title The Up and Down Arrow keys Arrow Keys allow you to navigate up and down between sub menu options Quick keys Quick keys are keyboard letter keys that are shortcuts to performing actions in the software Quick keys are displayed in a color different than the rest of a command Not all commands are available through their quick keys under every condition Sound Lab TDS Navigation Selecting a menu title from the main menu There are three ways to select a menu title from the main menu bar Mouse Point and click the menu title with the mouse Arrow keys Press the Right Arrow key or Left Arrow key to highlight your choice then press Enterto select it Quick keys Type the highlighted letter in the menu title such as the Din Display Exiting the menu No matter how you select a menu you can exit the menu close t
49. more details about the software see the section titled NC menus To make an NC measurement follow these steps 1 Choose Settings from the Input menu Choose the input setting and gain for your equipment arrangement To insure accurate readings adjust the preamp gain until you get an overload then lower it one step to arrive at the proper level 2 Choose Calibration from the Input menu Enter the calibration constant for your transducer 3 In the Parameters menu choose Noise Test NC and enter a value between 1 9999 seconds for the Integration Time 4 Choose Do Noise Test NC from the Measure menu or press 77 NC will start the test and measure the noise in eight octave bands When the test is complete the data will be displayed on the screen Sound Lab TDS Performing measurements Noise Test nil TDS File Parameters Display Input BO AE 05 TEF eu N p mermas 74 i a m EID brescia prince D T 1 r i j 1 D d T E CNET S NC ea IA eh a pf pri id e E TE ET eas EE o ECRIRE ze mj einlkg gau usteilaganarun ieygen cee ere tee nemmere reerd ree races errs ene sri iiae E Fea 354 AA SEER ee kn 6t A E Ru M Ta ies ie i een CA MU jec Li mter e UxeaTe o te do sadi pio dira eret eed SE a j 9t 9 4 3 ai at e i AD Ei zzulasqUMens masia Ma cl ri pa u ici IAS O Ra ae m A MEE WERL MO TENE A A ENEE uJ dt E O NE oi ia 3
50. of the reinforced sound and the time of arrival Performing measurements STI HASTI Adding noise to STI measurements Noise can be added to STI measurements from an NC noise criteria measurement or from a table The Add Noise to STU RASTIOoption in the Display menu provides a way to post process noise with noiseless STI or RASTI data When you have STI data displayed on the screen choosing Add Noise to STI RASTI opens a sub menu that allows you to choose noise values from an NC file or Table If you choose NC File a sub menu opens showing available files from which to extract noise data If you choose Table a sub menu will appear allowing you to enter noise values on octave band centers from the Illustration 5 12 Noise can be added to STI RASTI measurements from a file A or a table B under the Display menu keyboard The software will perform an FFT on the data with the noise included and redisplay the results FDS File Noise Table CFANOFF NC CFANON NC CFANONAS NC L 1 Octave 125 250 200 1000 2000 4000 8000 i b e d e f 2 RIt Info s H AIt Print ecalculate Hi ji El et Se ee TEs ECE 7 AROS x x 9 21 E 3 a r Qi O g mM 0 SEES measurements STI HASTI Evaluating the STI graph and summary table You may choose between two displays a graph or a table display An STI graph plots the individual STI s
51. on the screen You set the parameters for each display but you do not need to do this every time you make a measurement Instead you can change the display after the measurement is done Also in the Display menu you can e Turn On and Off display modes such as Cursor Difference and Overlay e Turn On and Off the mouse and the warning beep e Enter noise data into noiseless STI and RASTI data or add new noise into measurements already taken with noise e Change the display colors Display options The options for the display of data from measurements Frequency Response TDS gt p are arranged under the 3D Waterfall gt d NC _ Displaysub menu according STI to measurement type such Add Noise to STI RASTI as Time and Frequency pugna E e Response 3D NC and STI Difference ALt F2 En RASTI Cursor Fa HT60 Cursor Shift F2 Alt Mouse Alt Beep Adjust Colors Illustration 4 21 Display menu 4 41 4 42 Sound Lab TDS Display Menu Display options by measurement Time Response Displays time response or the output of a system vs time There are two types of time response displays which you can select under the menu item called Time Response Magnitude Shows energy vs time Heyser Spiral Shows the complete system response in one view a three dimensional curve in which the three projections are the polar real and imaginary planes Frequency Response Displays the frequency response There
52. only the amplitude and time of arrival but also the density of the field its ap proach to exponen tial growth and de cay and the initial signal delay Illustration 6 1 is a typical ETC The tall spike near the left edge is the direct sound from a test loudspeaker The height of the spike is not the highest point on the loudspeaker s frequency response curve It represents the total energy arriving at that particular time in this case from the loudspeaker Further to the right later in time reflections 6 2 may be seen arriving They have a lower total energy than the direct sound due to absorption and inverse square law losses Sound Lab TDS Practice measurements ail To make Time Response ETC tests the TEF analyzer sends a frequency sweep signal through the system under test in this case the system is a speaker microphone and air The electronic sweep tone fed to the loudspeaker will in effect represent all possible frequencies in the chosen sweep range The TEF analyzer then listens for the sweep via a microphone The frequency range of the sweep the sweep rate and the delay time plus other factors set by the operator all determine the characteristics of the ETC test display Reading an ETC display The first tall peak from the left represents the direct sound from the loudspeaker This is the sound that has traveled directly from the loudspeaker to the microphone in a straight line without
53. or 8192 lines Each line consists of the following items e A real number in scientific notation A tab character hexadecimal 09 e An imaginary number in scientific notation e An ASCII carriage return character hexadeci mal 0D for Macintosh files and a carriage return and line feed for MS DOS files hexa decimal OD OA Sound Lab TDS File formats mi Notes on ETC files Parameter label Value Comments EEC Always use this key word for ETC measurements Title xs Maximum of 50 characters Name on Maximum of 50 characters Date d Maximum of 50 characters Location oOo Maximum of 50 characters Description Maximum of 128 characters Save Rate k 47 Number of Samples 1024 Start Frequency 1 78E 03 Stop Frequency 2 22E 05 Sweep Time 4 01E 03 Sweep Rate 9 57E 03 Bandwidth 0 00E 00 Receive Delay 0 00E 00 ETC Data Window Type HAMMING ETC supports only five types of data windows All must be entered in upper case letters BLACKMAN HAMMING HANNING KAISER RECTANGULAR ETC Data Window Beta 2 00E 00 Beta is used only for Kaiser windows and must be a value between 2 and 15 Beta is always present regardless of the window type Reference Unit Pascal Volts Per Reference Unit 2 26E 03 Zero dB Reference Valu
54. parameters for the Noise Test Integration Time Enter a value here 1 9999 sec for the length of time in seconds that the data is to be averaged on each individual octave Line Output On or Off When turned on the Line Output allows you to monitor the octave band filtered noise at the output of the TEF through headphones an amplifier or a tape recorder 4 27 Sound Lab TDS Parameters Menu Guidelines for setting NC parameters Input levels have to be sufficient to yield valid results If the levels are set too low the resulting graphs will show abnormally low noise curves especially at the higher frequencies Ifyou are using the built in TEF preamps adjust the gain in the preamp until you get an overload then lower it one step to get the proper level If you are using a sound level meter and the line level input the output of the sound level meter should be in the range of 1 millivolt to 1 volt to perform valid NC measurements Due to the inherent noise of the computer and TEF your measurement setup should be in a different room from where the NC is being measured 4 28 Sound Lab TDS Parameters Menu Parameters STI RASTI STI When you choose Parameters STI RASTI a sub menu will appear and allow you to turn on Measure Noise and or Source Calibration Paraneters Time Response ETC Frequency Response 1D3 Noise Test XNC On Source Calibration OFf Alt Undo E o
55. pattern is an example of perfect modulation which equals an MTF of 1 0 The modulation pattern in Diagram B illustrates the effects of noise and reverberation in the room The modulation in the received sinewave is reduced by comparison because of the effects of noise and echoes Sound Lab TDS Performing measurements Introducing 3D 01 Introduction to 3D measurements Sound Lab 3D measurements made by the TEF analyzer are composed of 2 to 100 individual TDS frequency response measurements Each sweep is offset in time by a constant amount When all of the individual sweeps are displayed on the screen they form a three dimensional display that plots the frequency and time behavior of a system A 3D measurement shows how the frequency response of a system changes as the system response decays Ifyou have not made frequency response measurements we recommend that you become familiar with the material in this manual on making frequency response measurements Use the 3D display to simultaneously examine the time and frequency characteristics of rooms loudspeakers or electronic devices such as equalizers and filters For example you can see frequencies that ring they have a longer decay time than other frequencies 27 9 28 Sound Lab TDS Performing measurements Introducing 3D nil Measuring loudspeakers with 3D Arrange the measuring microphone and loudspeaker in an area that is free of nearby objects The distan
56. root of the sweep rate we are no longer doing TDS but are instead performing S 3 Q gt Q C O 0 Best Resolution and the F resolution V mill conventional swept spectrum analysis On the TDS side we have the advantage of a time resolution that is the reciprocal of the frequency resolution the frequency resolution is equal to 1 divided by the time resolution and allows good time selectivity On the conventional side while we can still get the same frequency resolutions that we can on the TDS side but we cannot get good time resolution By turning on Best Frequency Resolution in the Frequency Parameters menu you automatically set the bandwidth to the square root of the sweep rate and obtain the best possible frequency resolution for the current sweep rate Suppose the Best Frequency Resolution isn t good enough How can you get a better frequency resolution than the Best You simply increase the sweep time As you increase the sweep time and therefore decrease the sweep rate the bandwidth will automatically be reset to the square root of the new slower sweep rate yielding a new better frequency resolution When should you use Best Frequency Resolution Generally for acoustic measurements loudspeaker frequency responses etc you would not use it Looking at the graph you can see that when you have a very high frequency resolution small number the time resolution is very poor large number Th
57. see correctly nnn ee TDS If Bandwidth lt V Sweep rate then sweep rate Frequency resolution Bandwidth If Bandwidth V Sweep rate then COONS E imd Swept spectral Frequency resolution Bandwidth analysis Distance the smallest interval in length you will be able to resolve or see correctly Time the smallest increment of time that you will be able to resolve or see Bandwidth Sweep rate Time resolution Best Frequency Resolution TDS When Best Frequency Resolution is selected Sound Lab automatically calculates the optimum bandwidth to produce the best frequency resolution poorest time resolution for the sweep time that you have chosen Optimum bandwidth is the square root of the sweep rate sweep rate is calculated from sweep time and frequency span 4 21 4 22 Sound Lab TDS Parameters Menu Receive Delay TDS the difference in time between the start of the sweep and when the analyzer starts listening for the signal to return Bandwidth TDS The value entered here determines the size of sweeping filter i e what the filter can see See Appendix A How tbe TEF works Number of samples TDS the number of points during a sweep at which data will be recorded C C Change U Update NC No change Change entered 2 Sound Lab TDS Parameters Menu TDS Parameters oy amp U Resulting S amp E dk E change ENS of Wf eee pepe peu e
58. set the sweep time to be 3 4 times longer than the time you want displayed on the screen FPADGHITUDE toh Sound Lab TDS Practice measurements TOO ALcons Mil ETC display example To see an example of an appropriate ETC from which to calculate RT60 and 96ALcows open the data file called SNCTONLY ETC from the data which accompanied your Sound Lab TDS software This display is a Time Response ETC showing the first second of decay in a room with the sweep centered at 2000Hz This ETC display is representative of a reasonably well behaved 200 seat room A general look at the display without the cursors indicates coherent direct sound approximately 8 dB in level above the nearest reflec tion We see a reverberation time that is less than one second with no sig nificant arrivals later intime Just by look ing at the time re sponse raw data the room appears to be very good The ALcons calculation we will do takes all the above consider ations and puts them into one num ber Parameters Display Ernout 998 E E Bb E g TIME milliseconds Start Freq 1782 0 Stop Freq 2218 0 Illustration 6 20 Time Response ETC 6 27 6 28 Sound Lab TDS Practice measurements AT60 ALcons Parameters If you note the parameters used to set up for this display you will see that the start frequency of this test is 1782 and the stop frequency is 2218 This gives a center frequency of 2000 The 2
59. the data cursor Sound Lab TDS forms a data cursor with horizontal and vertical lines that extend across the data window The data cursor displays the value of the data at the intersection of the lines in an information box in the margin of the data window as shown in Illustration 6 J gt Turn the Cursor On in the Display menu TDE File MHeasure Paraneters Display rit E wee E bare A of have cal a lenasacans cl n uM E ag ae Lus adt enel AA ee A apy H 10 hw um c TER A A di Pe e 3 4 SL Ft TINE milliseconds RICE DINESETO Start Freq 200 0 Stop Freq 10000 0 Illustration 6 7 The data cursor 6 10 _ Sound Lab TDS Practice measurements mi Using the cursor to examine the data Position the cursor exactly on the first large spike in the display as in Illustration 6 7 This point represents the direct sound arrival at the microphone The information boxes at the edge of each coordinate of the cursor give important information for evaluation of the data Recall that your numbers may vary from this somewhat depending on the similarity of your testing setup to ours The vertical coordinate information box in our test displays the dB of the amplitude of the direct sound at 67 3 dB The horizontal coordinate information box shows the distance this sound traveled 5 41 ft and the exact time in milliseconds that it took to travel from the loudspeaker to the microphone 4 79 milliseconds
60. the file an If information box will ask you to confirm your choice and choose Yes or No Configuration Use Configuration to load save or erase global setup data Configuration files provide a convenient way to recall often used parameters Configuration files end in 7CF for TDS files All bna configuration files must be located in the same directory as the Sound Lab TDS program file Erase sub menu TDS ATEN Open Old Drive amp Dir Save as Shift F3 Erase TS Configuration Load AUGS TCr DATASHT TCF FACT1 TCF FACTORY TCF GRAY TCF GRAY1 TCF more Illustration 4 7 Configuration sub menus 4 7 Sound Lab TDS File Menu mil Printer settings Select from the choices in the menu Select a printer before choosing Print Graph Size The half page graph size option prints all data on one page The full page option prints the graph on one page test parameters and setup data are printed on a second page Resolution The medium and high resolu tion options determine print quality High resolution yields a better printout but takes longer to print than medium resolution Output Port Select the port that matches i the printer connection to your computer Print Sound Lab TDS prints the current data screen not including overlays to the printer using settings made in Printer Settings TDS Open Old Drive amp Dir Shift F3 Save as
61. the measurement The speaker and microphone are at the foci of the ellipsoid Sound reflections originating at the edge of the space window are attenuated 3dB and more distant reflections are attenuated by greater amounts O y S 3 a Qo Cr CJ 0 ossary Mill On the TEF analyzer the space window is determined by setting the bandwidth and sweep rate For example a 10 foot space window corresponds to a bandwidth of 88 5 Hz ata sweep rate of 10 000 Hz second at a sound velocity of 1130 feet per second at room temperature Formula B SD C where B bandwidth of the tracking filter in Hz S sweep rate in Hz sec D space window in feet C speed of sound 1130 feet sec The larger the space window the lower the frequency that can be measured accurately That is the frequency resolution increases as the space window increases Therefore a relatively large empty room is needed for low frequency measurement speech intelligibility A measure of sound clarity that indicates the ease of understanding speech It is a complex function of psychoacoustics signal to noise ratio of the sound source and direct to reverberant energy within the listening environment It is a function of signal level even in the presence of noise or reverberation Intelligibility is at a maximum with sound pressure levels from about 70 to 90 dB with a small decline in intelligibility at higher levels Below 70 dB intelligibility begins to dec
62. the validity of the entries under Drive and Directory Loading will delete current data Loading a configuration file will change the parameters thus invalidating the current data therefore the data will be deleted Measure halted Path is invalid Check the validity of the entries under Drive and Directory Measurement interrupted with curves saved When the 3D measurement is interrupted choosing the Continuebutton will continue the set of measure at the curve number that was interrupted Choosing the Stop button will cause the measurement to cease and update the number of curves to match the number that have already been made Choosing Ease will erase all of the curves that have already been saved for this measurement Min O Max 60 0 This message is seen only in the Settings sub menu Input gain can range from 0 to 60 in 4 dB increments Sound Lab TDS On screen messages iil Mode Diff Appears inthe lowerleft ofthe screen when Difference On has been selected in the Display menu Mode Ovr Appears in the lower left of the screen when Overlay On has been selected in the Display menu No TCF files Found Sound Lab didn t find a configuration file in the current path Obtain STI data before adding noise You can t add noise to an STI measurement before one has been made or a file opened Overload Occurred The input signal was too high Reduce gain at the input or lower the signal from the system under
63. time spans are needed as when measuring the acoustics of a reverberant room you will sweep narrow frequency bands When short time spans are needed as when examining the fine detail in a loudspeaker s time response you will sweep wide frequency bands Keep in mind the inverse relationship between Time and Frequency Doing a Time Response Test ETC Equipment arrangement The physical arrangement for these measurements consists of a room approximately 15 x 10 with a hard surface folding table a 4 inch single driver speaker and a B amp K 4007 measurement microphone You should get similar results with any convenient single driver speaker The microphone and speaker are mounted on stands approximately 1 1 2 feet above the table 5 1 2 feet apart on axis Connect the output of the TEF to the input of a power amplifier Keep in mind that the TEF 20 will output a one volt signal when the knob is set to the cal position Connect the output of the amplifier to the loudspeaker Plug the measuring microphone into the mic A connector of the TFF Sound Lab TDS Practice measurements all Start the Sound Lab TDS program Sound Lab TDS will remember the settings that you used when you last exited the program but if you have not yet used the program the default settings will appear To become familiar with measurement parameters we are going to set each parameter for an ETC measurement Setting Sound Lab TDS software
64. turn the Difference mode on 4 61 4 62 Sound Lab TDS adi Menu all The Difference mode lets you remove the frequency response of the loudspeaker when ve measure a microphone response Bt 1 Measure the response of the loudspeaker with a lab calibrated microphone 2 Turn on mode 3 N M asure the response f the joudspealter with the microphone under test 4 1 will be subtracted from 3 leaving only the microphone response C Sound Lab TDS Display Menu anl Other Display options Cursor Turn the cursor ONto read values of the data points on the graph The F2key also turns on the cursor Move the cursor along the graph by clicking the mouse or pressing the Arrow keys The Arrow keys move the cursor as follows Move left one data point Move right one data point Move right 1096 of the display Move left 1096 of the display Ctrl Move 10 data points to the left Ctrl 09 E 9 9 E Move 10 data points to the right Illustration 4 42 Arrow keys tbat move tbe cursor 4 63 4 64 Sound Lab TDS Display Menu TDS File Heasure Paraneters Display Input i i i i a A AR a a eS CETTE AS cs 20 4 1 AMPLITUDE tdB5 e uM 30 02 ms 356 53 fth 500 29 730 dar kamen eorom B75 i z e x TDS Delay 3D Start Delay 3D End Delay Start Freq 1780 0 Stop Freq Illustration 4 43 E Time response display showing the curs
65. with controlling software gives control of frequency energy and signal delay along with the precision to measure and analyze the results In addition TEF analyzers allow extensive post processing capabilities and storage of test data TEF analyzers can sweep linearly in time through a specified range of frequencies The characteristics of this oscillator are its sweep rate in hertz per second and its starting and stopping frequencies The analyzer in the TEF systems linearly sweeps its tuning through a range of frequencies Its characteristics are its sweep rate bandwidth and start frequency and stop frequency Since this bandwidth is sweeping in time it can also be described as a time window in seconds The analyzer time aperture equals the bandwidth in frequency hertz divided by the sweep rate in Hertz per second This window is proportional to bandwidth and is inversely proportional to sweep rate In mathematical terms R B S Time Resolution bandwidth sweep rate Sound Lab TDS Glossary mil anechoic Literally without echo A characteristic describing an environment whose boundaries effectively absorb all sound over the frequency range of interest thereby creating a free field condition By filtering out delayed reflections the TEF can make anechoic echo free measurements in a non anechoic room articulation loss of consonants A measure of speech intelligibility The percentage of consonants heard incorrectly
66. zero degrees Hessure Parameters ij Hr 20 8 Dap 73 83 par cals 3 0 00017 paacals i 0 0015 pascale Illustration 4 31 The Nyquist display Sound Lab TDS Display Menu mi Display options Frequency Response Heyser Spiral The amplitude of a complex waveform is the result of two factors called the real part and the imaginary part In a plane progressive wave in the free field G e before reflections occur the real part is proportional to potential energy and the imaginary part is proportional to kinetic energy The amplitude is equal to Amplitude V real part imag part and the magnitude is Magnitude Magnitude 10 log real part imag part The phase response can be found by Phase arc tan TL The Heyser spiral reveals that amplitude and phase are simply two different viewpoints of the same event Why measure phase e Phase is a more sensitive parameter to find the center frequency of filters e Phase reveals driver displacement something amplitude can only do very coarsely i e inverse square law whereas phase can show minute fractions of an inch e Phase is a clear detector of polarity e Phase reveals non minimum phase behavior 4 53 Sound Lab TDS Display Menu iil Paa IRARGI Ae PL Tm zx I a n I I i en gt i M rj He J eU ue c zem f i J yf i ees a a Aaa H E d ms u R h F a i i 1 mm Te Fu a inn 1 p mi a E
67. 12000 13000 14000 15000 16000 1700 18000 19000 200 6 22 Illustration 6 17 Frequency pbase response daia with receive delay set 0 05 millisecond later than Illustration 6 14 Illustration 6 18 A 0 01 millisecond adjustment to measurement in Illustration 6 15 creates an even flatter phase response nm LITUDE dg TDS AMPLITUDE CdH 3 J Q m 0 gt y 0 Practice measurements Measure Parar lara Dia Da RI EE I 1 T ED IA A RP UU O O IS TPPPHL Wht TIE sg lei a AE ti o 8 m 8 B a R n FREQUENCY CHa Dist Res 7090 5000 6000 200 1000 2000 ea 4000 FILE TIAS TOE Measure Parenwtiure Bo zo one ee Deas 3 hepi vet eee omer es res vi Sas deiode Ufer A ee co Pi 4000 3000 CUN EE 7000 E D o o N a j FILE TIM4 TOZ 3 14000 15000 L52 d5 sues Display 13000 14000 15000 al ian T 20 PT A AA ki rirerire mill 190 20 th o A a 2 PHASE Deg 30 6 23 Illustration 6 19 In this illustration we returned to the Parameters Frequency response menu and changed the distance resolution to actually include the reflection that was identified at the first peak of the ETC test we performed Setting the Resolution distance to 2 feet and re running the test caused this display showing the comb filtering produced by the reflection s presence
68. 4 Sound Lab TDS File forrnats nil STI ETC header block The ETC header in STI and RASTI files contain only those analyzer settings that would appear in an ETC Parameters sub menu The parameters used for the SII and RASTI tests are fixed by the program and cannot be changed by the operator The las line of the ETC header block is always Data STI ETC data blocks The second part of the ETC file is the collected data The number of samples is different for each frequency band of the STI measurement The data is stored as complex pairs identical to the storage format for ETC files C Sound Lab TDS File formats iil Notes on STI analyzer settings block Parameter label STI n FULL SIT NC NOISE Comments Always use this key word for STI and RASTI measurements Must be one of the following four key words FULL STI NOISELESS STI FULL RASIT NOISELESS RASTI Can be one of the following three key words NC NOISE If the measurement was a FULL SIT or FULL RASIT and the noise source was from an actual STI or RASTI measurement or the noise was brought in from a NC measurement then use the NC NOISE key word TABLED NOISE If the measurement was a FULL STI or FULL RASTT with noise and the noise source was from user entered table list then use the TABLED NOISE key word NO NOISE If the measure ment was a NOISELESS_STI or
69. A C Notes on NC files Parameter label NC Title Name Date Location Description Integration time Number of Samples Volts Per Reference Unit Channel Preamp Gain A Preamp Gain B Data format Data type Data count Data 4 16E 01 4 00E 01 3 15E 01 2 70E 01 2 22E 01 2 09E 01 1 33E 01 3 35E 01 Value 3 4 8 2 26E 03 3 60 TTA ASCII SINGLE 7 0 000000E 0 0 000000E 0 0 000000E 0 0 000000E 0 0 000000E 0 0 000000E 0 0 000000E 0 0 000000E 0 Sound Lab TD File formats al Comments Always use NC as the test type key word for NC measurements Maximum of 50 characters Maximum of 50 characters Maximum of 50 characters Maximum of 50 characters Maximum of 128 characters This value must be between 1 and 9 999 Default setting is 4 Number of Samples is fixed at 8 0 Line input B 1 Microphone input B 2 Line input A 3 Microphone input A Data count is fixed at 7 Data is in dB SPL 63 Hz band 125 Hz band 250 Hz band 500 Hz band 1000 Hz band 2000 Hz band 4000 Hz band 8000 Hz band Sound Lab TDS File formats mil CFANOFF NC THT Noise Criteria sienta With Ceili ing Fans tt CLJS JAB qe EN 327791 14 52 cummin Coal bush Church South Bend in Em n SETS Mic Just in F
70. B SPL Enter 0 00002 for this value e For other measurements enter the value that yields 0 dB For example enter 1 volt for dBV E oe Sound Lab TDS Input Menu mi Propagation Speed Highlight Propagation Speed and enter the propagation speed for the media in the system you are testing For example sound travels 1130 feet per second in air The number entered represents the distance a wave travels in one second in terms of your chosen distance unit For sound systems the distance unit is usually meters or feet Sound Lab software uses the propagation speed setting in several places to convert between time and distance Media Meters Second Feet Second Air 344 1128 Water fresh 1480 4855 Water salt 1520 4987 Glass 5200 17060 Gypsum board 6800 22310 Concrete 2400 11155 Wood soft 3350 10991 Aluminum 5150 16896 Mild steel 5050 16568 Lead 1220 4002 Plexiglass 1800 5905 Human body 1558 5111 Table 4 6 Speed of sound in various media at 21 C 4 79 4 80 Sound Lab TDS Input Menu Distance Unit Sound Laballows four distance units Usually this unit will be Feet or Meters depending on whether you want to use the English or Metric system of measurement The propagation speed automatically changes to match the units When you choose Distance Unit a sub menu appears allowing you to choose feet inches meters or centimeters To keep Distance Unit setting as displayed press Alt Clo
71. C r Sound Lab TDS Software User s Manual Crown International Inc 1718 W Mishawaka Road Elkhart IN 46517 4095 91997 Crown International Inc m toti c CANSA 6 97 Sound Lab il Irademarks The Techron TEF System 20 is manufactured by TECHRON Division of Crown International Inc Elkhart Indiana U S A under license from Jet Propulsion Laboratories California Institute of Technology Pasadena California U S A TEF TEF System 20 and TECHRON are registered trademarks of TECHRON Division of Crown International Inc Elkhart Indiana The trademark Sound Lab is licensed under United States trademark registration number 1 424 678 Apple and Macintosh are registered trademarks of Apple Computer Incorporated IBM and all IBM products mentioned in the manual are registered trademarks of International Business Machines Incorporated Motorola is a registered trademark of Motorola Incorporated MS DOS and Microsofts are registered trademarks of Microsoft Corporation The Techron TEF System 20 incorporates technologies requiring validated licensing upon export from the United States in accordance with U S Export Administration Regulations Acknowledgment Techron gratefully acknowledges the kindness of author and publisher in giving permission to reproduce their materials in Sound Lab for PC Software User s Manual Howard W Sams amp Co Basics of Sound from Intr
72. Conversely high sweep rates are used to Sound Lab TDS How TEF works ml increase time resolution at the expense of frequency resolution Frequency span The second parameter to set is the frequency range of the sweep This range should roughly correspond to the range over which useful operation of the system is to be expected Stimulus should not be applied for long durations which might damage the system Sweeping through zero Hertz is generally desirable when doing ascending TDS sweeps if you want improved resolution at low frequencies Most transducers will not be damaged by this practice if you avoid very slow sweep rates at high power levels Receive signal delay When making measurements involving a signal delay the third setting is the receive signal delay Normally you set the receive delay equal to the travel time of sound from loudspeaker to microphone T D C where T receive delay in seconds D distance between speaker and microphone in feet and C the speed of sound 1130 feet per second For energy vs time curves or ETCs the usual practice is to use a zero receive delay between the test and analyzer oscillations This is not necessary if it is B 9 B 10 Sound Lab TDS How TEF works hill known that no signal arrives at the analyzer before a certain delay If you program this value of delay the ETC display will start at this value of delay instead of Zero Bandwidth Swee
73. D 4 31 TDS 4 21 425 Binary saving TDS files as 4 5 Bottom of Scale 3D Waterfall 4 55 Frequency Response 4 48 4 49 4 50 Time Response 4 44 4 45 C Calibration 4 76 equipment arrangement 5 15 talker speaker 5 14 Center Frequency ETC 4 16 Channel 4 74 Clear All 4 5 Colors 4 66 COM port 2 3 COMI 4 81 COM2 4 81 comb filter F 4 commands 3 1 index 2 SOHO Lab TUS Index mi Communication 4 81 complex wave F 4 compression F 4 Configuration 4 1 4 7 coverage F 4 coverage angle F 4 crest factor F 4 critical distance F 4 frequency F 4 Cursor 4 63 relative 4 65 to examine data 6 11 Cursor is OFF D 2 Curve Order 3D Waterfall 4 55 4 56 4 71 Customer support 1 5 D data display options 4 41 interpretation C 1 storage disk directory 4 4 dB See decibel DC Shift Trigger 4 34 deadness F 5 decay rate F 5 decay time F 5 decibel F 5 delay F 5 destination drive path 2 2 Difference 4 41 4 61 diffraction F 6 diffuse field F 6 diffuser F 6 diffusion F 6 direct sound F 6 Direct to Reverberant Energy Ratio 6 29 disk drives See drive and directory display calibrating 6 5 Display menu 4 41 3D Waterfall 4 55 4 56 Add Noise to STI RASTI 4 59 Adjust colors 4 68 Alt Beep 4 72 Alt Mouse 4 72 Cursor 4 63 Difference 4 61 Frequency Response 4 42 4 47 4 48 4 49 4 50 4 51 NC 4 57 Overlay 4 60 RT60 cursor 4 66 SII 4 58 Time Response 4 42 4 44 4 46 Display Rotation Nyqui
74. Delay automatically enters the value at the point of the active cursor into the the Receive Delay option of the Parameters for the Fre quency Response test 3D Start Delay button automatically enters the value at the point of the active cursor into the Start Receiue Delay option of the Parameters for the 3D test 3D End Delay button automatically enters the value at the point of the active cursor into the End Receive Delay option of the Parameters for the 3D test 6 29 j 3 a Q gt O 0 Practice measurements RT6O ALcons Til Additional information You will also see additional information in boxes across thetop of the display which represent the software s best estimate for placing the cursors e RT60 0 62 Sec reverberation time or early decay time e EDir ERev 2 5 dB early direct to early reverberant sound ratio e Alcons 3 81 the V6ALCONS e dB down 10 5 the difference in level on the integration line between the left and right cursors These initial cursor in md ms fs mum em positions and val ues in the informa ni tion boxes repre sentthe computer s best estimate re garding placement Inspect the display carefully and make adjustments as nec MAGNITUDE dB dl co essary 10 n LI Y 20 T nn t H 1 1 i Li 50 46 n Hag us n g n R n n 5 D TDS Delay 3D Start Delay 3D End Delay Start Freq 1782 0 Stop Freq
75. Distance Unit For example if distance unit is set at 1130 feet second and you change to meters the value will automatically change to 244 4 meters second Table 4 5 Initial calibration settings 4 77 4 78 Sound Lab TDS Input Menu Reference Unit Enter the name up to 10 characters for the reference unit you want to use To set the reference unit choose Reference Unitand enter the new value The pascal is the standard reference unit for acoustic measuring If you are measuring voltages type Volt for impedance measurements enter Ohm Volts per Reference Unit Enter the sensitivity value from your microphone or transducer data sheet This value indicates how much voltage your transducer generates when one reference unit is applied to it For measurements with a microphone this value indicates how much voltage the microphone generates in a sound field of one pascal or 94 dB SPL For the B amp K 4007S microphone available from Techron a typical value is 2 26 millivolts per pascal entered as 0 00226 If you are measuring electronics and the reference unit is one volt type 1 Zero dB Reference Value This value indicates the zero dB reference value for your measurements in terms of your chosen reference unit Choose Zero dB Reference Valueandtype in the value that you wantto correspond to the 0 dB line on the measurement graph e For acoustics this value is 20 micropascals which corresponds to 0 d
76. EEPROM version numbers and date of software The Illustration 4 1 Go to command allows you to access other modules File menu that have been installed Quit the last command is the only proper way to exit Sound Lab 4 1 FIRST TDS FRSTMEAS TDS Alt Print Path Current Path CINN C NSLNDAT B Sound Lab TDS File Menu mu Open Old The Open Old command retrieves and displays stored data and allows you to navigate to other directories When you choose File Open Old a list box appears showing available file types from which to choose After you choose a file type a list box opens displaying filenames and or directories and subdirectories Filenames appear as a name plus extension e g FRSTMEAS TDS A directory or subdirectory has no extension and is enclosed by brackets e g DATA The represents the parent directory When it is highlighted press Enter or double click the mouse to change the path to the parent of the current directory or other directories No more than ten items can appear in the list box at any time The word more will appear at the bottom of any list greater than ten When you choose this option the listadvances to show more items Note The commands Erase and Configuration use the same or similar routine for file path navigation and file selection Illustration 4 2 File Open Old sub menus 4 2 Alt Info Illustration 4 3 Action buttons
77. F AA ee Ce AA ARA stop Frequency s A AA A ooo a a a n E T k E sweep Time oe an 44 Bandwidth as a a L1 E 45 Receive Delay 3 I D p EEE A O O O 1 _47 Dataformat MM NM i LCE ee A AE H 1 a E Saa cado A A St A A lr cR E ESA ce oe ne V Kn bie Pe pee es PS aata z AA L s E E 1 42E 0 1 6ZE 06 AAA CRA AAA AAA CLEE AAA A A A T EE LETTTLLTTEETTEETTTTELTTEETETTEETTTTEELETTEETTTTITEITEETELLEET 563 s a 7 HHHHHHHHHHHHHHHHHHHHHHHHHHHHI HHHH HHHHHHHHHHHHH H THHHHHHRHHHHHHH ee a te eee ee ll e el tell a a a err hint art ee ata tt ee tt tata tata tt ta AAA eee ee BO eat eee eee eee ee a aa aaa HA A A a a Pete a a a afa a a a eet et ea SE Nam Tura eee reer ae ea RERA H a a a E a EEEE H ca A HORARIA AAA atada tata tr tata tr tt ta ee a ta tt td BIB RH A ADA Bra A O PORC AAA PAD PALA APA A AO ee AAA A A AA ATE a el a te a e ll ee Illustration E 14 STI and RASTI ETC header block E 21 Notes on STI ETC block Parameter label BICI MES ETCS Save Rate k 94 Number of Samples 512 Start Frequency 11 0 Stop Frequency 228 0 Sweep Time 4 01 Sweep Rate 54 1 Bandwidth 0 0 Receive Delay 0 0000 E 22 Sound Lab TDS File formats mu Comments B a This is the key word for the start of the ETC data header If the meas
78. Front to Back and Back to Front describing the placement on the graph of the first curve measured The first curve is the one that is measured at the time set by Start Receive Delay Front to Back The first curve measured curve 001 is placed in the front of the graph Back to Front The first curve measured curve 001 is placed in the back of the graph be Illustration 4 36 The 3D Waterfall display Sound Lab TDS Display Menu iil Display options NC Noise NC Toggle this command to display the noise data as a Table or Graph NOISE TABLE TEF Octave Illustration 4 37 NC data displayed as a table i right and graph below TDE Fils Measure Paraneters Treat OCTAVE BAND SOUND PRESSURE LEVEL dB ref 2x10E6 5 pascal 63 i 50 500 1000 2000 23000 6000 Frequency Hz 4 57 Illustration 4 38 Table displays the STI value for each band plus the overall STI value Illustration 4 39 Graph displays the STI values on a graph 4 58 Display options STI STI This command toggles to display STI measurements as a Table or Grapb Goop EXCELLENT FAIA POOR BAD E A r Q O jw 0 Display Menu Haas ir Parameters TEF SPEECH IHTELLIDIBILITY TEST EARLY RT6O 1 20 1 23 L 16 0 48 n 49 S N RATIO 1 6 dB 1 3 dB 1 8 de Equivalent 3 N Ratio 4 0 dB Equivalent Early ATGO 0 93 5 SUBJECTIVE EVALUATION GOT File ShH BACK STI Noise source
79. Graph dB Display Rotation DO Degs Linear Octave Smoothing 0 0 X Illustration 6 12 Display Frequency Response parameters TOS AMPLITUDE CB FILE TIH1 TDS Sound Lab TDS Practice measurements ail Running the test Close the Display menu open the Measure menu and choose Do Frequency Test Again you will hear the sweep last for approximately two seconds It will sound different this time because we are sweeping over a different frequency band and the display will appear It should look similar to Illustration 6 13 depending on how similar your physical setup is to ours Press F2 to read the data with the cursor and determine the magnitude and phase signatures Phase Magnitude N Parameters PHARF Nerea ea o o0 9 E a DOGO a eo n a Q m m a N FREQUENCY Hz Dist Res 1 0 Freq Res 1130 0 4000 SOOD c e Og E 6000 11000 L Le Feed 17O00U iii Pd levee ace eec aves veri rFFE c rn 30 90 O e Eee Illustration 6 13 Phase magnitude data display Sound Lab TDS Practice measurements ml The vertical scaling on your display may be different since we are using auto scaling Recall we set up for a Linear scale which shows most of the detail in the high end of the frequency response where it occurs The og scale however compresses the high end obscuring this detail With a linear scale certain problems such as comb filtering a
80. Measure 1 0 i OVERALL STI i 0 71 GOOD ELE 4 A AA A AA a A hee mi errre eee ee BOE RO AAA EA ed ee ee ee BAN E AS A A EAE A AAA ep E i et A 0 5 er o A AA AAA AAA AAA 125 250 500 1000 FILE SANCBACK STI Frequency Hz 2000 4000 Noise source 38000 Heasure T able Illustration 4 40 Add Noise To STY RASTI submenu Illustration 4 41 Add noise options under the Display menu a from a file b from a table Sound Lab TDS Display Menu mi Other Display options Add Noise to STI RASTI Add Noise fron The Add Noise to STI RASTIoption provides a way to process noise with noiseless STI or RASTI data If you have no STI data on the screen you will be given a message Obtain STI data before adding noise Press any key to continue When you have STI data displayed on the screen choosing Add Noise to STI RASTI opens a sub menu that allows you to choose noise values from an NC file or Table If you choose NC File a sub menu opens showing available files from which to extract noise data If you choose Table a sub menu will appear allowing you to enter noise values on octave band centers from the keyboard and command the software to Recalculate the data The software will perform an FFT on the data with the noise included and redisplay the results TOS File Add Noise to STIL RASTI Noise Table Octave dB JEFES 125 2590 500 1000 2000 4000 8000 Rec
81. Note This number 4 79 milliseconds represents the receive delay that you will enter in the parameters to set up for the Frequency Response measurement we will do next By using the powerful cursor in Sound Lab TDS you can enter the receive delay directly into the Parameters Frequency Responsemenu To do this place the cursor on the peak of the direct sound and press F4 The receive delay is now entered into the Parameters Frequency Response menu for the Frequency response test TDS Fila Heasure TO AMPLITUDE Ci 10 bedhead FILE TIML ETC Illustration 6 8 Finding reflections 20 PSone eee A ee Sound Lab TDS Practice measurements mi Finding reflections Move the cursor over to the second peak to the right of the direct sound The information box tells us that at 5 91 milliseconds after the test signal energy at an ampli tude of 60 4 dB ar rived 6 68 feet out If you subtract 5 41 feet direct sound from 6 68 feet you see that there is a reflecting surface about 1 2 feet be yond the micro phone Looking at our set up the hard QR surface a little over a Serer eee foot away would Start Freq 200 0 Stop Freq 10000 0 likely be the table top Another way to do this would be to use the relative cursor Place the cursor on the direct sound and choose the Relative cursor button at the lower left hand corner of the display by pressing R or clicking on the button with the mouse Then
82. Rotation Horizontal Scale Octave Xmoothing Illustration 4 26 Frequency Response Display sub menu 4 47 3 a E C gt O uy Display Menu nl Display options Frequency Hesponse Phase The parameters that affect the Phase display are Top of Scale Bottom of Scale Auto Scaling Wrap and Horizontal Scale shown in gray Viu pue legc cepe decr cp ccc cc a 000005 E RET inet seas socle uncut Wrap When Wrapis toggled NODE Top of Scale 60 de 1 d RE qns Onthe phase curve will wrap or on start over at the top of the scale A oa ser Me ce pere cete agen luris Turin A eerie 180 Deus as frequency progresses The M ae top of the graph will be 180 NA degrees and the bottom will be po rooms hs d 180 degrees With Wrap off m ou s the phase curve will be Mn continuous withoutany sudden Octave smoothing 0 0 x 260 degree phase jumps or po transitions If you edit the Top of Scale or Bottom of Scale Wrap turns off Illustration 4 27 Parameters forthe Horizontal Scale Choose a linear or logarithmic Phase display of the display to set the horizontal frequency display scale frequency response Display the data on a Log scale to see a traditional frequency response use Linear to display signal delay problems such as comb filtering si J a Q C g 0 Display
83. S herean 4 16 rece neve PON onar eoe qut a a a aa tu OR 4 20 NOIE IS EE Neuesten statt oct ee A OR 4 27 ST RASIM STE S erase septem ettun amen c Rae ee 4 29 SIDE CU UD NIC UNE A A ag cee 4 30 STEN AV uns efl tees nien fed do taf 4 36 A 4 39 Display pull OA MSI a DAD 4 41 Time Response Magnitude cccccccccnonononanonononnonos PETS LS Tine Responses HEV SENS 6 dle and 4 46 Brest ncy RESPONSE ves Le sic eut ei di ideas 4 47 Erequeney Response dhe atero einst dT eee tem camus em sd 4 48 Frequency Response Magnitude AUR TE 4 49 Frequency Response Magnitude and Phase ess 4 50 Beeqmency Response NY Quist us cag cerneret san AAA 4 5 Frequency Response Heyser Spiral 4 53 a cor 4 55 NS iiic as 5 ERIE Bee pet agendo E A T E UM deett 4 57 O E OH M LO TO 4 58 CuleniPis play OPNS a ns eere cen rere Tea meme etd S ete 4 59 Summary of Display menu options sssseeeeeme 4 69 IECUDQUT Tace a o A D LU ET ONE 4 73 a E A A 4 74 Calibrate mes Menu commer ASES 4 76 Callilerauimie He display nina 4 76 Communication sulb imenu a esti oe LC A Due SNL Saal 4 81 Sound Lab Contents Section 5 Performing measurements 9 1 MECAUCHON uesdanm ciis cts ab ctam oh atten meen que md cams dinad ubt e acc ates 5 1 To make Sound Lab TDS tests eee CMT True A 5 1 Performing a time response test on a loudspeaker
84. Sound Lab TDS File Menu mil Four other commands are displayed Alt Close Closes the sub menu without making a selection Alt Fuli Expands the file information box showing files and directories with details such as file size date and time created Alt Brief appears in the file information box when you choose Ali Full Choosing Ali Brief collapses the file information box to a list box of file or directory names only If you want to revert to the file information box select Alt Full Alt Info If a filename is highlighted A t nfo opens a file information box containing the job description about that file If a directory name is highlighted the information box will show the current path and the path you can travel to if you press Enter Alt Print Selecting Alt Print will print the job description that was recorded with the Save Ascommand for each of the files listed in the sub menu Seven job description entries will print per page 4 3 Sound Lab TDS File Menu TOS Drive amp Dir DOS allows you to eroup files in directories The Drive amp Dir command allows you C 3 to select a drive and directory for Directoru Path NS E DAT AN E data storage or retrieval Sound Lab TDS defaults to drive C and directory SZ DATA Open Old Go to Quit Note The Drive and Directory will reflectany changes made when the File Open Old command is Illustration 4 4 used Drive amp D
85. TDS Basics of Sound mill Illustration A 4 shows the phase of various points on the wave E AMPLITUDE el 90 180 270 360 PHASE ANGLE Illustration A 4 The phase of various points on a wave If there are two identical waves but one is delayed with respect to the other there is a phase shift between the two waves The more delay the more phase shift Phase shift is measured in degrees Illustration A 5 shows two waves separated by 90 degrees 1 4 cycle of phase shift Foo PHASE SHIFT 20 _ BETWEEN WAVES AMPLITUDE 0 90 180 270 360 PHASE ANGLE OF SOLID WAVE Illustration A 5 Two waves 90 degrees out of phase The dashed wave lags the solid wave by 90 degrees A 5 Sound Lab TDS Basics of Sound ail When there is a 180 degree phase shift between two identical waves the peak of one wave coincides with the trough of another If these two waves are combined they cancel each other out This phenomenon is called phase cancellation Harmonic content The type of wave shown in Illustrations A 2 and A 5 are called sine waves A sine wave is a pure tone of a single frequency such as produced by a tone generator However most musical tones have a complex waveform which has more than one frequency component Yet no matter how complex all sounds are combinations of sine waves of different frequencies and amplitudes Illustration A 6 shows sine w
86. a E e eR e e cee A 3 PAN ULI Cl ae m ee Cc Ee cer ime S D ud A 3 iU aries FeO lies oorr chek ease unde g teet towne ears oed necis a A 4 Phasen oi phase SUMING Ge eise tat o E Cams I Desi ns nears omini A 4 The phase OR Vvaniows points ona WAVE ueteres tienen A 5 PIAA o A e dee 0 c em A 6 Behavior of sound in rooms senene ea a eene on TT A 7 BS GLO ENT TN Aer aaa lt a NINTENDO RnR A 7 REVEN AO ne rs ee A 9 PR Se i eset HIS Nc HAMS geie ii eeen issu EE EE D Perte ORDRE A 11 ROOM modes mesa ironia A 11 Sound Lab Contents ail Appendix B How TEF measurements work B 1 Reflections can be kept out of measurement ccccccnononnnonincnonacanananicnnnnnos B 2 Relationship between Time Frequency esse B 3 I UrieTabratiS OPE 2m A dotum con unteibe mies t B 4 Measurement resolution eee NUR AENEAM MEME ot Ih ud qm B 5 Trade off between time and frequency ener ene a B 7 nterrelated AT ATM e Su ure pere A ASES ei B 8 SWEED TAE oc a 00 B 8 Bre gue ncvuspatii iia ES TA O IE B 9 Recamestsionabidelas aldo ta B 9 TS AME IGEN wee rra lee trim ni pt B 10 SPACE window considerations cerceii E B 12 Appendix C Data O C 1 JESS US Cee 1010 20 2 O bns ae T o etra e E C 1 evite ce MANS asi ra cit mig esee oe UE E SOLE als eect C 2 Some UMM O WAENI A A trier eee tod eem C 4 Appendix D n screen messages D 1 Appendix E ASCII file formats E 1 aa o MA A a E 1 Data lock do
87. adecimal 09 e An imaginary number in scientific notation e An ASCII carriage return character hexadeci mal 0D for Macintosh files and a carriage return and line feed for MS DOS files hexa decimal 0D OA E 9 Sound Lab TDS File formats mi UU S9 18 01 Location 30uth Bend EM Description Church Eun Save Rate k EN NN a stunn E ta a ECH E HT EIHE E POPPER errr Tere errr Creer Cie rei Cert ret CCPC rit nA SA E AA E sta N E z s Number of Samples 1024 HE as REE CH ETARA DITA A DHO a ose a a 5 2 006 02 Distance Resolution _ CA ERRE LFLIM m E PreampGain MEME EM PreampGainB IA 0i m Output Level DIL Tum I xMe ANE Asi ao NEU i HE Illustration E 9 TDS ASCII beader displayed in a spreadsbeet The double quotes are not displayed by tbe spreadsbeet E 10 SS o Notes on TDS files Parameter label TDS l Title gt Name Date Location Description Save Rate k Number of Samples Start Frequency Stop Frequency Sweep Time Sweep Rate Bandwidth Time Resolution Distance Resolution Frequency Resolution Critical Bandwidth On Receive Delay Reference Unit Volts Per Reference Unit Zero dB Reference Val
88. alculate D n ij Ue moueat CFANOFF NC CFANON HC CFANONAS NC NIE a Alt Full Alt Info b c d e t a h A A 4 59 4 60 Sound Lab TDS Display Menu ttl Other Display Options Overlay _ Sound Lab TDS allows you to overlay time frequency or NC measurements Overlay allows multiple curves of the same type to be placed on the screen at the same time If Overlayis On the screen is not erased between each measurement Each new measurement curve is simply drawn over the curves of the previous tests Data stored on disk may be overlaid by turning on Overlay and choosing Open Old from the File menu Overlay only works for data gathered for common measurement types For example if a time response is onthe screen you cannot overlay a frequency response Any command that erases the screen will destroy any multiple curves built up on the display For example if Overlay is On and a series of frequency response curves is displayed on the screen performing a time response test will erase the screen The overlaid curves exist visually only on the screen If the cursor is turned on when multiple curves are on the screen the cursor will read only the data from the most recent test Auto scaling is ignored when Overlay is turned On Parameters may not be changed while Overlay is turned on However data files of the same type may be overlaid even if the parameters are different Overlay is
89. and geophysics Unfortunately long before he could transfer the abundance of all his thought into realities he died suddenly in 1987 carrying much unfinished business with him A man before his time Heyser some have said was the Newton of our age It remains to be seen as time delay spectrometry continues to grow with better equipment and software to make practical use of Heyser s theory The Techron division of Crown International takes particular honor in its good fortune of being one avenue in which the thinking of Richard Heyser is becoming available in useful terms to people solving problems in sound analysis We therefore dedicate this manual to the memory of Richard Heyser the remarkable man who gave us a new theory in which to not only observe but to continue to work as well Richard C Heyser received his B S E E degree from the University of Arizona in 1953 Awarded the AIEE Charles LeGeyt Fortescue Fellowship for advanced studies he received his M S E E from the California Institute of Technology in 1954 The following two years were spent in post graduate work at Cal Tech leading toward a doctorate During the summer months of 1954 and 1955 Mr Heyser was a research engineer specializing in transistor circuits with the Motorola Research Laboratory Phoenix Arizona From 1956 until his death in 1987 he had been associated with the California Institute of Technology Jet Propulsion Laboratory in Pasadena California wh
90. andwidth and time offset of the tracking filter you can study the spectrum of the direct sound by itself certain reflections or both 10 kHz sec gt T 0 T21 2 millisecond Illustration B 1 A filter sweeping over frequency of interest B 1 B 2 Sound Lab TDS How TEF works mill For example A 20 Hz wide filter sweeps along at 10 000 Hz second For clarity the filter is drawn with a rectangular shape The edges of the rectangular filter correspond to the 3 dB down points of a real filter At the left edge the frequency of interest f is just entering the filter s bandwidth At the center of the Illustration B 1 the filter has swept higher in frequency and is tuned to the frequency of interest At the right the frequency of interest is leaving the filter the filter having swept still higher Quite simply the TEF puts an exactly measured signal into a system it knows exactly when to listen for it to emerge and knows exactly how to figure out what these results mean Heflections can be kept out of measurement Suppose a 1000 Hz tone is swept to the microphone through the air At that instant the tracking filter center frequency is set to 1000 Hz Now suppose that the loudspeaker s sound reflects off a wall and enters the microphone after a certain delay By the time the reflection enters the microphone the tracking filter will have swept to a higher frequency than the reflection as shown in Illustrati
91. asks such as memory managers or print queues Sound Lab DS On screen messages Parameters may not be changed while overlay or difference mode is on Turn off Differenceand Overlay mode before changing parameter S Performing FFT This message appears during STI or RASTI measurements An FFT is a complex operation which may take several minutes on computers without math co processors This message also appears when changing the noise with Add Noise Heceiving Data This message indicates the PC is receiving test data from the TEF over the HI or serial port Besolution m st be greater than O A resolution of zero is a physical impossibility RT6O cursor is on or RT6O cursor is off These messages are seen only when the data screen is empty and the cursor status has changed Cursors are not visible when the screen data does not match the test parameters HTBO out of Range This message is seen when Sound Lab places the RT60 cursors in a way that would result in an increasing slope If this condition were true the sound field would be increasing not decaying To correct this problem manually place the cursors as described in the section titled Making ALcons and RT60 measurements D 7 D 8 Sound Lab TDS On screen messages ui Start frequency should be Bandwidth A Bandwidth that is less than the bandwidth will cause an invalid response for the low frequency end of the measurement Test Interrupted Du
92. at you determined in this calibration procedure If the gain control of the amplifier is changed perform the calibration procedures again 9 17 0 E Q r Q C 0 Performing measurements STI RASTI iit Following the EQ test the test is paused and a dialog box informs you e Source Calibration procedure is completed e Source Calibration is being turned off e You may arrange equipment for the STI RASTI test You continue the procedure by pressing any key See Illustration 5 10 below Parameters Displau Source Calibration procedure completed Turning off Source Calibration Arrange equipment for STI RASTI test Press any key to continue Illustration 5 9 Dialog box preceeding STI sweeps house speaker house house amplifier microphone test microphone talker loudspeaker Sound Lab TOS Performing measurements STI RASTI Arrange the equipment for STI 1 Place the source loudspeaker where the orator will speak and adjust the height of the loud speaker to be about head high 2 Place the test microphone in the position of a human listener 3 Turn on the house system and set the levels for normal operation 4 Press any key to resume the STI RASTI tests Pressing any key causes a LE ein ie Save As dialog box to pop up allowing you to name the STI e measurement and create o 03 05 1994 12 15 35 7 testing notes before GE continuing
93. ate is calculated from sweep time and frequency span When the bandwidth is larger than the square root of the sweep rate the frequency resolution is equal to the bandwidth Under this condition the TEF performs similarly to conventional swept sine wave analysis and will properly measure the peak amplitudes of narrowband stationary signals such as hum and noise however fine detail may be passed over in the frequency response Also because time resolution decreases reflections may be included in the measurement of the direct sound 4 25 4 26 Sound Lab TDS Parameters Menu mi S TDS A A o 3 8 ej f al B Parameters amp S of EEE S S 2 S E ej 9 59 sS S oe C EJ au S el E FBS C Ch EJE Bf el E S o 8 E E U Update Resulting EP amp E E E E EJ E 5 3 NC No change change SJ FJ EJ SJE NL al Of me al entered Ed Stop frequency Y nee ila Bandwidth Calculated by Sound Lab gt Jupe A a Table 4 3 Interdependent parameter relationships for Frequency Response TDS tests Best Frequency Resolution On Sound Lab TDS Parameters Menu Parameters Noise Test NC To perform a noise test you set the Integration Time and specify if you are using the Line Output of the TEF Parameters Time Response ETC Frequency Response XCTDS Inteqration Tine Line Output Off alt CIose White Noise Sine Wave Tone Frequency Illustration 4 16 The
94. aves of three frequencies combined to FUNDAMENTAL form a complex wave SECOND E MEME z E N The amplitudes of the various waves are added HARMONIC algebraically atthe same point in time to obtain the final complex waveform RESULTING COMPLEX WAVEFORM rd SUM OF THE THREE WAVES ABOVE Illustration A 6 Addition of fundamental and harmonics to form a complex waveform Sound Lab TDS Basics of Sound The lowest frequency in a complex wave is called the fundamental frequency It determines the pitch of the sound Higher frequencies in the complex wave are called overtones or upper partials If the overtones are integral multiples of the fundamental frequency they are called harmonics For example if the fundamental frequency is 200 Hz the second harmonic is 400 Hz 2 x 2005 the third harmonic is 600 Hz 3 x 200 and so on The number of harmonics and their amplitudes relative to the fundamental partly determine the tone quality or timbre of a sound They identify the sound as being from a trumpet piano organ voice etc White and pink noise contains all audible frequencies and has an irregular non periodic waveform Behavior of sound in rooms So far we ve covered the characteristics of sound waves traveling in open space But since most music is heard in rooms we need to understand the acoustic phenomena created by the room interior surfaces
95. brations in a medium in the frequency range 20 Hz to 20 000 Hz soundabsorption The change of sound energy into some other form usually heat in passing through a medium or on striking a surface sound decay The dying of sound energy to equilibrium sound intensity The rate of flow of sound energy through a unit area in a specified direction The watt per square meter is the unit of sound intensity F 23 F 24 Sound Lab TDS Glossary mill sound level a term applied to data taken on instruments which meet the specifications for sound level meters drawn up by the American National Standards Institute CANSD sound level meter an apparatus for estimating the equivalent loudness of noise by an objective method sound power The total sound power in watts radiated by a source sound pressure level SPL Sound pressure level in decibels of a sound is 20 times the log to the base 10 of the ratio of the pressure of this sound to the ref pressure Pref dB SPL 20 log P P ref where P ref 0 90002 pascal The value of pref should always be stated A common reference pressure used in connection with hearing and the specification of noise is 0 00002 pascals sound reflections See reflections sound wave The periodic variations in sound pressure radiating from a sound source space window An ellipsoid space around the speaker and microphone inside of which sound reflections are included in
96. ce tothe nearest object will determine the lowest frequency you can measure see Space window considerations in Appendix B How TEF works Position the microphone on axis with the loudspeaker The following suggestions assumes a distance of five feet between microphone and loudspeaker 1 Make an ETC Set the ETC parameters for a short time span about 20 milliseconds to determine arrival of the direct sound and the first reflection and when the sound from the speaker decayed into the noise of the room 2 Set the Start Delay Turn on the RT60 cursor Shift F2 and press L to make the left cursor active To set the start delay position the left cursor just before the direct sound arrival and enter the value into the 3D parameters by pressing S 3 Set tbe End Receive Delay Make the right cursor active and set the End Delay by placing it at the point where the direct sound decays into the noise or just before the arrival of the first reflection whichever occurs first Press Eto enter the value into the 3D parameters The time between the Start and End Receive Delay is typically 2 or 3 milliseconds when measuring a tweeter or high frequency horn Illustration 5 16 A Sound Lab 3D display of a small speaker system Fo 2 000 TIHE ma Sound Lab TDS Performing measurements Introducing 3D Set the Time Resolution In the Parameters menu under 3D Test set Time Resolution to a value five times longer than the Rec
97. ch intelligibility A full STI test is accomplished by measuring seven individual one second time span ETC s at each of seven octave center frequencies between 125 Hz and 8 kHz After each ETC test the modulation transfer function MTF is calculated and the STI in each octave band is computed The TEF test generator level at each octave band is adjusted to match the average spectral content of speech At the conclusion of the test the overall STI value is computed by taking a weighted average of the individual octave band STI values see speech intelligibility STC Standard Transmission Class A single number rating for describing sound transmission loss of a wall Or partition sweep rate The rate in Hz second of a TEF sweep It is the measure of how fast frequency is changing with respect to time sweep time The duration of a TEF sweep swept sine wave A sine wave made to vary uniformly in frequency from low to high or high to low A frequency modulated sine wave F 27 F 28 Sound Lab TDS Glossary ill TDS time delay spectrometry A method conceived by Richard Heyser that permits a spectrum that has been delayed to be measured with the signal delay removed TDS measures in the frequency domain then transforms the results mathematically for interpretation in the energy frequency ortime domains In general terms TDS is a way to measure energy passing through a system TDS measurements describe what effect
98. choose Do STI Test under the Measure menu A series of dialog boxes will lead you through the procedure and then the software will proceed directly into measuring the STI See Calibration procedure to follow _ Sound Lab TDS Performing measurements STI HASTI mil Performing the measurement with calibrated talker speaker This section details the basic steps for making an STI measurement with noise included and assumes you are going to perform the accompanying calibration and equalization tests of the talker speaker To make an STI measurement follow these steps Equipment arrangement for calibration 1 Place test microphone and talker loudspeaker one meter apart on axis An alternative distance placement is 1 2 meter apart 2 Connect the input of the test amplifier to the test output of the TEF Connect the output of the test amplifier to the talker loudspeaker Connect the test microphone to either channel A or B of the TEF test microphone 1 meter talker test amplifier loudspeaker Illustration 5 7 Typical equipment arrangement to perform STI calibration procedure 5 15 Sound Lab TDS Performing measurements STI RASTI mil Setting up parameters 1 Under the Input menu check that your input settings gain calibration and communication values and are set appropriately for your equipment setup 2 Choose table or graph in the Display STI menu 3 Choose Measure Noise On
99. cores in octave bands tate OVERALL STI 5 Ea a j w a 3 3 i 1 E 0 4 hata espacios agp anoo gt aD Sy SS ea een AA JM Ce eec A 10 000009 MU ON OR ON gel a L 0 3 i aM E ERN CENE GAA UM aM AME JN NON 0 2 a ELA E kcr RD Mp ciere i Sites EE as 2 ied re Mae A E a REOR YT TEUER US WM ECE or reri menn e RT A EEE DOIT Sol UREN ERN CUM A 3 0 0 125 za 500 1000 2000 4000 6000 Frequency Hz Noise source Heasure Illustration 5 13 STI data displayed as a graph 9 22 Performing measurements STI RASTI STI summary table display The STI table display shows numeric values of the individual and overall STI data Shown are the STI scores the equivalent early reverberation time and the equivalent signal to noise ratio S N Ratio TEF SPEECH INTELLIGIBILITY TEST OUERALL STI D 23 Equivalent EZH Ratio 6 6 Equivalent Early AT amp O 11 13 s SUBJECTIVE EVALUATION File BALCONY STI Noise source Measure Illustration 5 14 Summary STI table display 9 23 9 24 Table 5 1 STI RASTI to ALCONS conversion table Sound Lab TDS PD measurements STI RASTI anl The subjective evaluation The STI subjective score correlates with spoken word articulation tests These tests are conducted with a speaker reciting a phonetically balanced word list for a panel of listeners who record what they hear Subje
100. ctive evaluation STI score Bad 0 to 0 3 Poor 0 3 to 0 45 Fair 0 45 to 0 6 Good 0 6 to 0 75 Excellent 0 75 to 1 0 Signal to noise ratio This column indicates the signal to noise ratio that would yield the STI score if no reverberation were present This assumes that only noise without the effects of reverberation is present in the transmission chain to degrade intelligibility Early RT60 The early RT60 column indicates the value of the early decay time that would yield the STI score if no noise were present This assumes that only reverberation effects are present in the transmission chain to degrade intelligibility The reverberation process assumed in this calculation is a perfectly linear decay on a dB basis but with no noise Converting RASTI measurements to AL Bad Poor Fair Good Excellent CONS RASTI 0 20 0 22 0 24 0 34 0 36 0 50 0 52 0 64 0 66 0 86 0 88 1 0 AL CONS 57 7 51 8 46 5 27 0 24 2 11 4 10 2 5 3 4 8 1 6 1 4 0 0 Sound Lab TDS Performing measurements STI RASTI mil About the STI measurement process The modulation transfer function MTF is a measure of the preservation of speech modulation patterns necessary to maintain high speech intelligibility when a signal passes through a system Classical methods directly measure the MTF with sinewave amplitude modulation of a band limited random noise carrier signal These methods make a series of modulation transfer measurement
101. d curve 001 is placed in the back of the graph NC Toggle this command to display noise data as a Table or Grapb STI This command toggles the type of display for STI measurements Table displays the STI value for each band plus the overall STI value Grapb displays the STI values on a graph Overlay allows multiple time frequency or NC measurements to placed on the screen at the same time Difference Time or frequency measurements can be differenced The Difference mode is toggled On or Off After a reference curve is established it is subtracted from succeeding curves and the differenced data is displayed on the screen 4 71 Sound Lab TDS 4 72 Display Menu mu Cursor Turn the cursor Onto read values of the data points on the graph Move the cursor along the graph by clicking the mouse or pressing the Arrow keys RT60 cursor The RT60 cursor is toggled on or off When the RT60 cursor is On Sound Lab performs an integration on the time response data and displays it in a second color Three cursors can then be moved across the data to perform RT60 calculations and a ALcons calculation Alt Mouse Turns off the mouse operation Alt Beep Turns off the beep warning Adjust Colors Adjust Colors allows you to choose from sixteen colors for the various elements of the display Current colors are shown along with a list of color choices Sound Lab TDS Input Menu ail Input menu se
102. d Heyser Spiral displays TDS HNaanure Parmasaterz Disoloy Input i TEF 20 g o fused NETTE i Fi E eA 4 y i y X hs Yi i a A z ue ehe PA J ae kA A J i i rd 3 EI i boda 1 t fi SF 5 2epo88289828989 8B o Q o 0c O O 8 6 0 amp 8 u188 53528 5565 d do d H 4 d N FREQUENCY CHz gt Dist Res 1 0 Freq Hes 11430 Illustration 5 3 Magnitude Display of the Frequency Response test 9 7 Sound Lab TDS Performing measurements Noise Test iml Noise criteria measurements NC Noise Criteria Curves are a standard method of characterizing noise loudness The NC rating has been used extensively in noise and vibration measuring Noise Criteria measurements NC can provide important information for designing a sound system or evaluating a noise problem NC measurements are made with ANSI Type 2 filters Equipment needed To make NC measurements you will need an MS DOS computer a TEF 20 analyzer Sound Lab TDS software a tripod and a high quality microphone An alternative to using a microphone is a sound level meter with a line level output NC measurements with a microphone The microphone inputs of the TEF 20 are wired to accept industry standard 3 pin XLR type connectors The microphone connector provides phantom power for condenser microphones Illustration 5 4 Equipment arrangement for microphones 0 9 3 c J a e Q T jw 0 Performing measur
103. d source is shut off It is calculated by measuring the rate of decay over at least the first 25 dB to 30 dB of decay and extrapolating what the RT would be if the decay continued at that rate rarefaction tThe portion of a sound wave in which molecules are spread apart forming a region with lower than normal atmospheric pressure The opposite of compression receive delay In TEF the difference in time between the start of the sweep and when the analyzer starts looking for it reflection The bouncing or return of a sound wave from an object lasger than one quarter wavelength of the sound When the object is one quarter wavelength or slightly smaller it also causes diffraction of the sound sound bending around the object refraction The change in direction of a sound wave that occurs when sound passes from one medium to another from air to glass to air or through layers of air with different temperatures reinforcement See sound reinforcement relative phase The phase of one sine wave compared with another resolution The amount of detail we are able to resolve or see in the quantity that we are measuring F 19 F 20 Sound Lab TDS Glossary mi resolution frequency Amount of detail we are able to resolve or see in the frequency domain Measuring with 1 kHz of resolution will smear any details that have a repetition in less than 1 kHz The effect of poor resolution on a frequency response
104. d surfaces etc Sound Lab TDS Glossary Fourier transform A mathematical description of the relationship between functions of time and corresponding functions of frequency It is a map to convert data from one domain into another For example if we have a signal that is a function of time an impulse response for example then the Fourier Transform will convert that time domain data into frequency data yielding a signal that is a function of frequency a frequency response The inverse Fourier Transform will do just the opposite It will give the time domain data from the frequency domain The Fourier transform is executed by the computer in the TEF when making Energy Time Curves free field An environment in which there are no reflective surfaces within the frequency region of interest frequency The number of complete cycles or vibrations per unit of time usually per second The frequency of a wave measured in hertz Hz is equal to the velocity divided by the wavelength A low frequency sound say 100 Hz has a low pitch a high frequency sound say 10 000 Hz has a high pitch Frequency is a measure of oftenness The units of frequency are reciprocal of the units of time frequency resolution see resolution frequency Sound Lab TDS Glossary mi frequency response Amplitude versus frequency plot In TEF measurements energy density versus the frequency for a selected time window When stated as
105. de One quantity is considered leading or lagging the other by the phase difference Sound Lab TDS Glossary pink noise A test signal containing all frequencies Cunless band limited with equal energy per octave Pink noise is a test signal used with real time analyzers for equalizing a sound system to the desired frequency response and for testing loudspeakers pitch The subjective lowness or highness of a tone The pitch of a tone usually correlates with the fundamental frequency polar pattern tThe characteristie pattern of a microphone and loudspeaker A graph of microphone sensitivity plotted vs angle of sound incidence Some examples of polar patterns are omnidirectional bidirectional and unidirectional Subsets of the unidirectional pattern are cardioid supercardioid and hypercardioid patterns polarity The positive or negative direction of an electrical acoustical or magnetic force Two identical signals in opposite polarity are 180 degrees apart at all frequencies Polarity is not frequency dependent post processing data Processing measurement results after performing test sweeps precedence effect The effect of two sounds approximately 20 milliseconds apart that are coming from two places but which we localize to be at the location of the earlier arriving sound pre delay Short for pre reverberation delay The delay about 30 to 100 milliseconds between the F 17 F 18 Sound Lab TDS
106. dge to 22 2 milliseconds on the right Close the Parameters menu 6 7 Sound Lab TDS Practice measurements mil Setting up the screen display gt Open the Display menu and select Time Response Select Magnitude under Display Type and turn Auto Scaling On if it is not already on The Auto Scaling feature insures that the screen fills with the data you have selected Close the Display menu Time Hesponse LETC Heyser Spiral Magnitude Heyser Spiral Illustration 6 5 Display parameters for tbe Time Response test 6 8 Sound Lab TDS Practice measurements mi Running the Time Response test gt We are now ready to perform the Time Response measurement Open the Measure menu and choose Do Time Test You will hear the sweep last for approximately one second and will see the ETC display appear on the screen You should get a display that looks similar to Illustra tion 6 6 depending on the similarity of your physical room setup to ours and the levels Press F2to activate the data cursor Note Excessive drive is not necessary to get valid data Set the volume to a comfortable level TDS an dr Fur aria Er Drm Lang Tusce T dd uu ETA li j W f i A my mir V WM L an m ma Apdo Tn em tS IE Lauda au Pd 10 A pm 165 i n 3 n A Illustration 6 6 The direct sound is the highest peak in this ETC _ Sound Lab TDS Practice measurements The power of
107. e 2 00E 05 Propagation Speed 1 13E 03 Parameter label Distance Unit Channel Preamp Gain A Preamp Gain B Output Level Data format Data type Data count Data FEET 60 4 0007 ASCII SINGLE 1023 Sound Lab TDS File forrnats Comments Distance Units can only be expressed in one of four key words Note all are upper case FEET INCH METER CENTIMETER 0 Line input B 1 Microphone input B 2 Line input A 3 Microphone input A This is the output level used for this ETC The output level value cannot be positive and is expressed in dB below 1 0 volt rms This value is valid only when the front panel level control is in the Cal position Data types can only be expressed in two key words SINGLE and DDOUBLE There is currently no support for DDOUBLE This is a zero based count Data count is always equal to Number of samples 1 This is always the last line of the header and precedes the data Sound Lab TDS File formats ALTARFB ETC THT ETE Taken To Show F m NOU Mant fat LS ZJAB E RUE 15 49 BENE UTI DNA E E Description 7 Save Rate k KA e Number of Samples 3 9 een Frequens deam L FEET a 10 A Eien omer DE 12 Sweep Rate 13 Bandwidth _ 14 Rec
108. e LETE 100 0 Hz Stop Frequency 10000 0 Hz Center Frequency 5050 0 Hz Frequency Span 9900 0 Hz Sweep Time 1 0 s Receiue Delau 0 0000 ms Tine Span 43 9596 ns Number of Samples 1024 Hindou i Hanning Illustration 4 14 Parameters for the Time Response ETC test Start Frequency ETC the starting frequency of the sweep Stop Frequency ETC the ending frequency of the Sweep Center Frequency ETC the frequency halfway between the start and stop of the sweep This is entered automatically when you set start and stop frequencies Sound Lab TDS Parameters Menu TIT Frequency Span ETC range of frequencies start to stop over which the TEF sweeps Sweep Time ETC the duration of a TEF sweep Receive Delay ETC the difference in time between the start of the sweep and when the analyzer starts listening for the return signal Time span ETC the time during which we listen for the effects of the signal on the room or system It is shown in Time Response ETC measurements on the x axis on the screen Number of samples ETC the number of points during a sweep at which data will be recorded Window ETC the user may select a Blackman Hamming Hanning Kaiser or rectangular window for use in processing the data Note Sound Lab will not allow you to change to a frequency span or time span that would require a start frequency below 100 Hz Instead Sound Lab will make the following se
109. e criteria curves modulation transfer function A measure of how well the amplitude modulation variation of intensity with time of a signal is preserved when the signal is sent through a particular transmission chain Research has shown that a good portion of the intelligence in F 13 F 14 Sound Lab TDS Glossary mill human speech is contained in the modulation of the speech waveform Preservation of the speech modulation patterns is important to maintain high intelligibility Noise echoes and reverberation are found to decrease the effective modulation of the speech waveform and hence impair intelligibility See STI and RASTI Nyquist display A plot of the tip of a vector that is changing in both length and angle as the frequency sweeps The length of the vector is proportional to the magnitude of the energy and the angle of the vector represents the phase of the signal In 3 D space the Nyquist Curve is like a corkscrew or a spiral when viewed end on with the frequency axis pointing directly towards us real and imaginary components plotted as a rotating phasor These are extremely useful in showing the partitioning of kinetic and potential energies frequency by frequency Energy lying on the imaginary axis vertical is kinetic Energy lying on real axis horizontal is potential energy The ratio of imaginary to real is the ratio of kinetic to potential energy at that frequency Don Davis octave The
110. e test signal to the device under test and gathers analyzes and displays data about the output relative to the input of the device Sound Lab TDS measures traditional parameters such as frequency response and phase response along with a number of TDS specific measurements such as time and distance and energy time frequency curves Sound Lab TDS software displays and stores data on a variety of microcomputers but requires the Techron TEF 20 analyzer to make measurements and collect data Unpacking Sound Lab TDS software contains the following items e User s manual e 1 44M 3 5 Distribution disk e Function key template 1 1 Sound Lab TDS 1 2 Introduction mil Typical equipment for acoustical measurements In addition to Sound Lab TDS software you may need the following equipment e MS DOS computer 20MHz 386 with math coprocessor e TEF 20 analyzer e Microphone e Power amplifier e Speaker e Hard drive or formatted disks for storing data What you need to know This manual assumes your familiarity with 1 MS DOS and utilities that came with your computer 2 your mouse and its installation and operation and 3 general acoustics and sound system design About this manual This manual is a reference manual for Sound Lab TDS and is not intended to be a tutorial on how to make acoustic measurements The remainder of the manual contains sections to help you start using Sound Lab TDS Section 1 Intr
111. e that the peaks and notches are evenly spaced Each notch is approximately 1389 Hz apart as is each peak Widely spaced notches indicate that the signals are arriving fairly close together Notches close together indicate that the signals are separated farther in time 400041 6000 anog 2a 3 a v in FREQUENCY CHz gt Sound Lab TDS Data Interpretation nil Illustration C 3 has a linear scale On a logarithmic scale this signature of two interfering signals would be very difficult to see This is one of the reasons for the growing popularity of linear scales This type of interference pattern may be caused by the direct sound from a loudspeaker and a reflection or it could be the result of two drivers covering the same frequency range but emitting their sounds at slightly different times When making frequency response measurements you must take the frequency resolution into account Remember that in order to reliably measure a frequency you must have enough time to observe at least one full period If we have a frequency resolution of 500 Hz the resulting time resolution is 2 msec The period of a 500 Hz sound wave is 2 msec This means that with 500 Hz of frequency resolution all frequencies below 500 Hz are not being reliably measured The analyzer will display what may look like reasonable data below 500 Hz and in fact we can consider a part of it to be reliable A rule of thumb is that from a frequ
112. ect sound verified in the ETC We will enter 1 foot Distance resolution to attenuate everything over 1 foot from our measurement Notice how this entry automatically changes the Frequency and Time Resolution to correlate as these parameters are interrelated It also changes the bandwidth to 9 1 Hz Setting the analyzer in this way will cause the TEF to attenuate the reflection by 15 dB Note You rarely have to set the Sweep Rate and Bandwidth to do a frequency response They are automatically set for you when you select the Sweep Time and Resolutions 0 O t 3 a tC Q C 0 Practice measurements mil Setting the screen display When we measure frequency with the TEF analyzer both magnitude and phase data are recorded during the frequency sweep Magnitude and phase are two different ways of looking at the same data The data from a Frequency Response measurement can be displayed showing phase magnitude magnitude and phase the Nyquist or Heyser Spiral depending on the settings you choose in the Display menu Open the Display menu and make the following settings Display Time Response ETC Frequency Response TDS Display Type Magnitude Magnitude Top of Scale a 30 dB 30 Auto icaling On Bottom of Scale Phase Top of Scale Botton of Scale 180 Degs Auto Scaling On Hr ap Off Nyquist Top of Scale 90 dB Bottom of Ecale Auto Scaling
113. ee pe pe pe eae pepe e fe beers pepe a mee jejejejeje v e e e coda Table 4 2 Interdependent parameter relationships for the Frequency Response TDS test Best Frequency Resolution OFF 4 23 4 24 Sound Lab TDS Parameters Menu mi Guidelines for TDS measurement parameters Use an ETC measurement to determine the exact time of arrival of the sound you want to analyze Set the receive delay to equal the time of arrival Set sweep time to be as short as possible to achieve the desired results See PECs A How TEF works Sweep time effects the quality of the measure ment the longer the sweep time the greater the noise immunity Select start and stop frequencies that cover the frequency range of interest Stop frequency must be greater than start frequency by 1 Hz Start frequency must be greater than or equal to the bandwidth for a valid test When Best Frequency Resolution is On Sound Lab calculates the optimum bandwidth and all resolutions see the next section Bandwidth must be greater than or equal to 2 Hz and less than or equal to 240 Hz Sound Lab TDS Parameters Menu mi Best frequency resolution and optimum bandwidth When Best Frequency Resolution is On Sound Lab automatically calculates the optimum bandwidth to produce the best frequency resolution poorest time resolution for the sweep time that you have chosen Optimum bandwidth is the square root of the sweep rate sweep r
114. eive Delay dis E DD 15 ETC Data Window Type _ HAMMING i 16 ETC Data Window Beta 2 OOE O0 17 Reference Unit Pascal 18 Yolts Per Reference Unit 2 26E TH 19 zero dB Reference Yal E 2 0DE 05 20 Propsptionspeed 1 13Ee05 i em O a A TETT A SE 087 aba rd bd 4 5GE nra ama 3 15E 06 459E 06 Illustration E 1 ETC ASCH file displayed with a spreadsheet The spreadsheet does not display the double quotes in the header E 6 Sound Lab TDS File formats ail NC ASCII files The NC header The first part of the NC file is the header information The header is a record of all analyzer settings that contributed to the test Also included in the header are operator comments test location and the date the test was made See Header information format at the beginning of this section Line 16 the last line of the header is always Data The NC data The second block of the NC file is eight lines of collected data The data is stored as sound pressure level expressed in dB These values include factors entered in the Calibration sub menu of Sound Lab Each line of NC data contains the following items e A sound pressure level in scientific notation e A tab character hexadecimal 09 e Zero expressed in scientific notation e An ASCII carriage return character hexadeci mal 0D for Macintosh files and a carriage return and line feed for MS DOS files hexa decimal OD 0
115. eive Delay Step set by the start and end receive delay The ratio of time resolution to Receive Delay Step is called the overlap ratio Perform the measurement Start the 3D measurement by pressing F9 or Quick key 3 Examine the display and repeat the measure ment with different parameters if desired 9 29 9 30 Sound Lab TDS Performing measurements Introducing 3D mi Measuring rooms with 3D When measuring a room with 3D test excite the room in a manner typical of its use For example suppose you want to examine the low frequency behavior of a concert hall Set the loudspeaker in the location where bass sound originates and place the microphone in the listener s position Set the frequency span of the measurement to cover the range of the bass frequencies of interest 1 Make an ETC Set the parameters for a long time span about 5 to 10 times longer than the time it takes for sound to travel from front to back in the room Use the cursor to examine the ETC and determine when the direct sound arrived and where the sound decayed into the noise of the room 2 Set the Start Receive Delay Turn on the RT60 cursor Shift F2 and press Z to make the left cursor active Position the left cursor to the point where the direct sound begins to rise and enter the value into the 3D parameters by pressing S 3 Set the End Receive Delay Press Rto make the right cursor active Move it to the right to where the
116. eld you may press the Left Arrow key to navigate to the left in the string The Home key will jump to the beginning of the string Press the Right Arrow key to navigate to the right in the string The End key will jump to the right end of the string Then press Enterto store the settings When you re setting a series of parameters it s more convenient enter a setting then press the Down Arrow This enters the setting and tabs down to the next edit field Then you can type in the next setting and so on If you enter a setting that the program can t use the closest valid setting will be displayed To charge a setting you typed re select the edit field and re enter the data To cancel an edit you just made press ESC while the edit field is highlighted Sound Lab TDS 3 6 Navigation il Toggle choices If a command provides a choice between two options a toggle switches between the two alternate choices To switch between the two choices re select the command Or you can toggle the setting by clicking on the setting with the mouse How to undo what you entered Many sub menus have a command called A r Undo Choosing Alt Undo resets all the sub menu parameters to the settings they had when the current sub menu was opened The Undo feature works only until the sub menu window is closed You cannot reopen the window and undo those changes To use Alt Undo e Using your mouse point and click on Alt Undo e Press the Do
117. elength F 30 weighted F 30 White Noise 4 39 Window ETC 4 17 4 18 space F 24 time F 29 Wrap Phase 4 48 4 50 Z Zero dB Reference Value 4 77 6 6 Zero sweep rate B 8 index 1 1
118. ements Noise Test Mill If you are using the built in TEF preamps adjust the gain in the preamp until you get an overload then lower it one step to get the proper level Note Be aware that all microphones have inherent self noise and if you are measuring an extremely quiet room the self noise of the microphone could adversely affect your measurement Check your microphone specifications for this information It may help to have your measurement setup in a different room from where the NC is being measured NC measurements with sound level meters If you are using a sound level meter and the line level input the output of the sound level meter must be in the range of 1 millivolt to 1 volt to perform valid NC measurements To connect a sound level meter connect the output of the meter to the TEF 20 line input and set the AC DC switch to AC Illustration 5 5 Equipment arrangement for sound level meters Sound Lab TDS Performing measurements Noise Test ll Setting the AC DC switch to AC will prevent small dc voltages generated by the sound level meter from causing premature and otherwise unexplained input overload errors Additionally be sure to understand how the meter range settings affect the output level Consult the technical manual supplied with the sound level meter before attempting an accurate calibration Making NC measurements This section details the basic steps for making an NC measurement For
119. ency that is equalto 1 2 ofthe frequency resolution on up the data is reliable With 500 Hz of frequency resolution we can consider everything from 250 Hz on up to be reliable Noise is another problem to watch out for TDS is highly immune to noise and unless you are using high sweep rates in a very noisy environment noise should not be a problem in TEF measurements However the ETC measurement is more susceptible to noise due to the wider filter bandwidths that are used C 6 TES au Ao 30 AMPLITUDE dE 10 FILE FIGUREJG ETC ao Hipo e E 3 Q F Q c g Un Data Interpretation mi Illustration C 4 shows a noisy ETC Although the direct sound is easily seen at a level of 42 dB the rest of the display is noise If all you were interested in was the time of arrival and the level of the direct sound it s there However if you were trying to measure the room you would have to increase the level from the loudspeaker in order to bring the room s reflections up out of the noise Measure Paraneters Display Input TEF 20 TIME milliseconds gt Start Freq 100 0 top Freq 44000 C Illustration C 4 A noisy ETC showing the direct sound at 42 dB Sound Lab TDS On screen messages ail Appendix D On screen messages This appendix lists some on screen messages that you may encounter while using Sound Lab Other messages may also appear with possible solutions Follow t
120. er the timeresolution decreases bigger number So while we have better frequency resolution and can see more detail we are no longer able to reject reflections quite as well In practice we must always G 1 G2 Sound Lab TDS Best resolution and the TEF Resolution V mi find a happy compromise between the time and frequency resolutions As you change the frequency resolution in the Frequency Parameters menu you will notice that the Bandwidth value changes as well Remember that the frequency resolution is notequal to the bandwidth of the filter In the TDS process the bandwidth of the sweeping filter along with the speed at which it sweeps the sweep rate determines the resolution of the measurement For TDS the frequency resolution RJ is equal to the sweep rate SR in Hz s hertz per second divided by the bandwidth BW in Hz R SR BW As you change the resolution the computer calculates a new bandwidth that will yield the resolution you requested for the current sweep rate The sweep rate being determined by the Start Frequency Stop Frequency and Sweep Time The better the frequency resolution smaller number the larger the bandwidth Intuitively you would think that to increase the frequency resolution you would have to reduce the bandwidth of the filter This would allow you to look at a narrower portion of the spectrum This is true for conventional swept spectrum analysis but not for TDS Lets l
121. er of Curves 37 Pause between curves 0 0 s Test Sequencing Automatic A1t CTose 8T Undo Illustration 4 18 The 3D parameters menu Start Frequency 3D the starting frequency of the sweep Stop Frequency 3D the ending frequency of the sweep Sweep Time 3D the duration of a TEF sweep Sweep rate 3D the rate in Hz second of a TEF Sweep ak Sound Lab TDS Parameters Menu mi Resolution 3D the smallest increment that can be correctly discerned in a parameter you have chosen Frequency the smallest increment of fre quency that can be correctly discerned in the frequency domain Distance the smallest interval in length you will be able to resolve or see correctly Time the smallest increment of time you are able to see or correctly resolve in the time domain Best Frequency Resolution 3D When Best Frequency Resolution is selected Sound Lab automatically calculates the optimum bandwidth to produce the best frequency resolution poorest time resolution for the sweep time that you have chosen Optimum bandwidth is the square root of the sweep rate sweep rate is calculated from sweep time and frequency span Start and End Receive Delay 3D These two parameters determine the time span between the first and last measurements The software will allow the values to be equal making this measurement useful for collecting polar data Start Receive delay 3D The recei
122. eral tests See additional comments in Overlay command description 4 45 Sound Lab TDS Display Menu il Display options Time Hesponse Heyser Spiral The Heyser Spiral display shows the complete system response in one view a three dimensional curve in which the three projections are the polar real and imaginary planes When the display is on the screen you can press F1 to open a sub menu which gives key combinations for various manipulations of the display Illustration 4 24 Tbe Heyser Spiral display of a Time Response test Illustration 4 25 Rotate plot left or right Left or Right arrow The Help menu Tilt plot up or down Up or Down arrow a Move plot up or doun PageUp or PageDoun appears when you Move plot left or right or gt Increase rotation and move steps Alt 1 press F1 Decrease rotation and move steps It D Expand time and frequency axis AIt Compress time and frequency axis Alt C Return to original positian Hone Press any key to continue 4 46 Sound Lab TDS Display Menu mil Display options Frequency Hesponse When you select Display Frequency Response Display Type you may choose one of five display types Phase vs frequency Magnitude vs frequency Magnitude and Phase Nyquist Heyser Spiral Display Magnitude and Phase Magnitude Magnitude and Phase Nuquist Heyser Spiral Nuaqu list Top of Scale Bottom of Scale Auto Scaling Graph Display
123. ere he was a senior member of the JPL Technical Staff Sound Lab Contents Contents Trademarks Acknowledgment Dedication Section 1 Introduction 1 1 Unam aos E AEE 1 1 Typical equipment for acoustical measurements seee 1 2 Viray OWE Need iron A a a a 1 2 About tliis manual ECO OU MEG 1 2 CUSTOMER SUPPO aF R E A ossi us RR 1 5 Section 2 Sound Lab TDS Install program 2 1 Copynshts cice M B T mnm 2 2 Selecta COM POR accounts ca rias 2 3 Check install selections Se NM ia 2 5 File ANSIEN ccs iccescseenncenaoennvoens H aaa tp eens 2 5 lien eee UU IL Mw 2 6 Section 3 Navigation in Sound Lab 3 1 Navigation Sem EAD a ides mito o cct da cs 3 1 A gene nT eerste cater es nr a a S Lance Md 3 2 Selecting a menu title from the main MENU 1 0 cece eetteeeeees 3 3 EXAMEN RM 3 3 Selecting menu items A A 3 4 Entering information in a sub menu cccccooononcnnnnnononananononnncnnnnnonnnnanons 3 5 How to undo what you entered en obsit Besoin us 2 6 Helpful features for working with the software suse 3 7 Moving from module to module ini bp istos 3 8 Sound Lab Contents mill Section 4 Menus for the TDS module MA E E E E T A 4 1 Measte me Mea aa a uie Caps wr aa yi cra CPUS 4 11 Patameters mentadas aaa E N n um 4 15 Settine WEST parameters saccus met qae o osa e pcs Meee 4 15 Time Response ERC Pamete
124. eric pressure than normal These disturbances are passed from one molecule to the next in a spring like motion to pass the wave along The sound waves travel outward from the sound source at about 1130 feet per second At some receiving point such as an ear ora microphone the air pressure varies up and down as the disturbance passes by Illustration A 2 is a graph showing how sound pressure varies with time It fluctuates up and down like a wave hence the term sound wave The high point of the graph is called a peak the low point is called a trough The horizontal center line of the graph is normal atmospheric pressure PEAK Y ABOVE NORMAL NORMAL TIME BELOW NORMAL A TROUGH Illustration A 2 Sound pressure vs time of one cycle of a sound wave J NES PEAK AMPLITUDE Sound Lab TDS Basics of Sound Characteristics of sound waves Illustration A 3 shows three successive cycles of a wave One complete vibration from high to low pressure and back to the starting point is called one cycle The time between the peak of one wave and the peak of the next is called the period of the wave One cycle is one period in time long P ONE PERIOD IN TIME M i ONE CYCLE ONE CYCLE ONE CYCLE Illustration A 3 Tbree cycles of a wave Amplitude At any point on the wave the vertical distance of the wave from the center line is called the amplitude of the wave The amplitude of the peak is ca
125. es between Vector or Magnitude Choose the averaging type you prefer Number of Sweeps Avg Sound Lab will make from 2 to 999 sweeps in the averaging process Pause Between Sweeps Avg A value entered here determines the number of seconds the TEF waits between sweeps Sound Lab TDS Parameters Menu anl Test Sequencing Avg When you choose Test Sequencing a sub menu allows you to select one of four waysto startthe sweep The choices are Automatic Keyboard DC Sbift Trigger and Pulse Trigger Automatic When you choose Automatic Sound Lab makes each sweep with the pause between them the number of seconds set in Parameters 3D Test Pause between curves Keyboard When you choose Keyboard the software waits for you to press a key before making the next sweep DC Sbift Trigger This option is available to work with a remote push button accessory connected to the TEF through the external trigger connector When DC Shift Trigger is selected the software begins the measurement when signaled by a push button See sche matic in analyzer user manual Pulse trigger This option was designed specifically to be used with an accessory turntable connected to the TEF through the external trigger connector For specific turn table details refer to the instructions from the manufacturer 4 37 4 38 Sound Lab TDS Parameters Menu Guidelines for averaging Vector averaging With vector averaging the co
126. exists D 5 Performing fft D 7 Receiving data D 7 RT60 out of range D 7 Start frequency should be D 8 Test Interrupted D 8 Test Timed Out D 8 Testing D 8 The printer is not ready D 8 The TEF is not responding D 9 a There is not data D 9 Time span should not exceed sweep time D 9 modulation transfer function 5 25 modules changing 4 9 mouse 3 2 4 41 MTF See modulation transfer function N NC Noise about the display 5 11 curves 5 12 display 4 43 4 57 file format E 6 measurements 5 10 Parameters 4 28 rating 5 12 table or graph 4 57 near field F 13 Noise adding to STI RASTI 4 41 ambient F 1 pink F 17 signal to noise ratio F 23 Noise criteria measurements See NC Noise noiseless test 4 12 Number of Curves 3D 4 33 Number of Samples GD 4 33 ETC 4 17 TDS 4 22 Nyquist F 14 Sound Lab TDS Index mi Frequency Response 4 51 O octave F 14 Octave smoothing 4 51 4 70 Frequency Response 4 49 4 50 4 51 Nyquist 4 51 off axis F 15 On screen messages D 1 Open Old 4 2 Output Pink noise 4 39 Port 4 8 Sine Wave tone 4 39 White noise 4 39 Overlap ratio 5 31 Overlay 4 41 4 60 overload 4 75 5 11 p Parameters 4 15 guidelines Frequency Response 4 24 SII 5 16 Time Response 4 18 interdependent 4 15 Menu 3D test 4 30 Averaging 4 36 Frequency Response 4 20 Noise Test 4 27 STI RASTI 4 29 Time Response 4 16 6 3 parent directory 4 2 index 7 Path changing 44 Pause Between Curve
127. frequency response test L See equipment arrangement for Time Response test Start the Sound Lab program Set the input parameters Go to the Input menu and select Settings Select the settings and gain for your equipment arrangement From the Input menu select Calibration and enter the proper values and calibration constant for your transducer From the Input menu select Communication and enter the proper values Perform a time response test ETC to find the direct sound Turn on the Cursorin the Display menu by selecting Cursor On or pressing function key F2 Position it over the exact time of the first energy arrival at the microphone Press F4 or select the TDS Delay button at the bottom of the screen to enter the receive delay into your measurement parameters for the Frequency Response test Setting the measurement parameters From the Parameters menu select Frequency Response Enter the parameters under which you want the test conducted Sound Lab TDS Performing measurements Time and Frequency Response mi 9 At this point you may run the test by selecting Do Frequency Test under the Measure menu 10 Refine the receive delay to flatten the phase response by pressing F4 and entering the incremental changes you desire Press Enter and retest 11 From the Display menu select Frequency Response to view the data in other displays You can choose Phase Magnitude Magnitude and Phase Nyquist an
128. fy EL when you run a test i C A test signal that is too loud can damage a speaker or cause distortion Illustration 5 1 Equipment arrangement for performing Time and Frequency test of a loudspeaker 0 2 Sound Lab TDS Performing measurements Time and Frequency Response TI Start the Sound Lab program Set the input parameters Go to the Input menu and select Settings Select the settings and gain to match your equipment arrange ment From the Input menu select Calibration and enter the proper values and calibration con stant for your transducer From the Input menu select Communication and enter the proper values a If you do not have a TEF HI card installed enter 57600 for the Baud Rate of the com port If you do have a TEF HI card installed the baud rate doesn t matter b If you have a TEF HI card installed select HI port Otherwise select COM1 or COM2 depending upon the port to which you con nected the TEF c Use the HI Base default 308 Setting the Display From the Display Menu choose Time Response then from the Display Type submenu select Magnitude Turn Auto Scaling On Setting the measurement parameters Go to the Parameters menu and select Time Re sponse test Enter the parameters under which you want the test conducted For more infor mation on setting parameters see Section 4 Menus Guidelines for setting parameters 0 3 9 4 Sound Lab TDS
129. g area coverage angle The angle included between 6 dB down points of a sound source crest factor The ratio of peak to rms values of a waveform critical distance The distance from a sound source at which direct sound and reverberant sound are at the same level critical frequency The frequency below which standing waves cause significant room modes dB Abbreviation for decibel see decibel px Sound Lab TDS Glossary mi deadness The lack of sound reflections in a room The subjective judgment of how a room sounds dependent upon the initial time delay gap and the ratio of direct sound level to the early reflection level decay rate decay time The rate at which the reverberant sound field decays in a room measured in dB second Decay rate is related to reverberation time by R 60 RT decibel dB A power ratio The unit of measurement of audio level Ten times the logarithm of the ratio of two power levels Twenty times the logarithm of the ratio of two voltages currents or sound pressures dBV is decibels relative to 1 volt dBm is decibels relative to 1 milliwatt dBA is decibels A weighted see Weighted A decibel is commonly thought to be the smallest change in sound pressure level that the trained human ear can detect delay The time interval between two signals Delay can be 1 thesignaldelay time through a given component 2 the signal delay time from a loudspeaker to
130. h frequency displayed on the horizontal axis magnitude and phase on the vertical axis TDt Fije Measure Paranmetars Display Input ALi TUDE Cun FREQUENCY CHz gt Bist Res 3 8 Freq Res 300 0 Illustration 6 10 A typical logarithmic display of frequency phase data Use the Frequency Response TDS measurement to e find comb filters e examine the direct sound frequency response e set crossover points in speaker systems e verify manufacturer s claims e equalize the sound system confirm polarity of microphones and speakers e and to measure impedance over a wide frequency span C Sound Lab TDS Practice measurements mu As before we will send a sweeping test signal into the loudspeaker and examine the data that is returned to the analyzer When we make frequency response measurements with the TEF we set the tracking filter of the analyzer to listen at the right time See Appendix A How the TEF works This time is the time offset or receive delay we confirmed in the Time Response ETC test just performed Setting the parameters for the Frequency Response Test gt Open the Parameters Frequency Response menu and look at the parameters You will see that the Receive Delayof 4 91 milliseconds or whatever number that you measured for your particular setup is already entered when we pressed Fin the Time Response display with the cursor on the direct sound The first decision
131. having been reflected by some object The horizontal position of the direct sound on the display indicates its time of arrival the horizontal scale is time in milliseconds Its height indicates its level the vertical scale is amplitude in dB Immediately following the direct sound in Illustration 6 1 and continuing out to about 5 milliseconds is the decay of the loudspeaker The various peaks extending from about 5 milliseconds out to the right side of the display represent reflections in the room The time span on an ETC display full scale from left to right is dependent on the frequency span of the sweep and the number of samples The computer changes the start and stop frequencies to provide the frequency span that combined with current number of samples selected provides the requested Time Span Remember the inverse relationship between the units of time and frequency a value that is wide in one domain will be narrow in the other domain A very narrow pulse in the 6 3 6 4 Sound Lab TDS Practice measurements time domain results in a very wide spectrum in the frequency domain A wide sweep in the frequency domain results in a short full scale time in an ETC For more information see Appendix A How the TEF Works You set the time span for ETCs in the Parameters Time Responsemenu When you enter a time span the computer automatically changes the start and stop frequenciesto provide the requested time span When long
132. he on screen instructions that accompany these messages to resolve problems Messages listed in this section appear in alphabetical order according to the first word in each message Awaiting TEF trigger TEF is waiting for trigger signal at the external trigger connector Bandwidth should be gt sqrt sweep rate A bandwidth that is greater than the square root of the sweep rate is not a TDS measurement and therefore does not reject reflections Can t difference Number of points doesn t match Both files must contain the same number of data points in order to difference them Can t difference Different file type You can t difference a time and a frequency file Can not save 1 this file type You can t use Save 1 with STI RASTI nor 2D D 1 Sound Lab TDS On screen messages il Check Communications or Check Communication Port This message appears when the host PC fails to communicate with the TEF analyzer Check the match between the hardware settings Section 5 TEF 20 Analyzer manual and the selections made under the Communication sub menu For serial communications check the baud and COM port settings For HI check the base address setting Also either interface could have a faulty cable Turn ac power to the TEF offand then on or press Reset on the analyzer front panel after making changes Cursor is Off or Cursor is On These messages are seerr only when the data screen is empty a
133. he unit of frequency is defined as the reciprocal of the unit of time then mathematically the unit of time is the reciprocal of the unit of frequency The mathematical descriptions of this relationship between time and frequency are Time 1 Frequency T 1 F where T is the period in seconds and F is the frequency in hertz and Frequency 1 Time F 1 T where F is the frequency in hertz and T is the period in seconds The product of time period versus frequency will always equal one Time x Frequency 1 T x F 1 For example if we have a 20 Hz sine wave we can calculate its period as being 1 20 or 05 second If we measure the period of a cyclic process to be 1 second then its frequency is 1 0 1 or 10 Hz This reciprocal relationship is always present and needs to be considered when setting parameters Sound Lab TDS How TEF works ail Measurement resolution When any quantity is measured it is always limited in its resolution or how much detail we can see or resolve Resolution is the degree of clarity with which we can observe or measure something For example you can look at a butterfly with the unaided eye and Observe its coloration and veining and you can see that it has intricate markings If you examine closer with a magnifying glass you will be able to see more fine detail of its markings because you have increased the resolution of your view If you place a butterfly wing under a microscope yo
134. he window by Seeing Alt Closein any of the three ways Mouse Point and click Alt Close Arrow keys Press the Down arrow key to Alt Close and press Enter Quick keys Hold A t and press C 3 3 3 4 Command Sound Lab TDS Navigation Selecting menu items After you select a menu title a sub menu appears with a list of commands on the left and their settings on the right Selecting an item will invoke one of three things e A new sub menu e A highlighted area called an edit field e A toggle or switch between two settings Magnitude Magnitude Quick keys Top of Scale Bottom of Scale Auto Scaling Alt Close A1t Undo Action buttons Illustration 3 3 Sub menu options Edit field reverse type when selected U Reference Unit Sound Lab TDS Navigation Entering information in a sub menu Choose the item you want with the mouse Arrow keys or highlighted letter Edit field some items require you to type pascals b e aa DI ouzz6 x information in an edit field Zero dB Reference Ualue 0 00002 When you select one of Propagation Speed Distance Unit Illustration 3 4 Edit field 1130 0 these commands a space edit field is highlighted where you can enter numbers or text from the keyboard feet It is not necessary to erase any highlighted numbers or text When you begin typing the new data replaces the old To edit information in the highlighted fi
135. in the ST RASTI option in the Parameters menu 4 Turn Source Calibration ON in the STI RASTI option in the Parameters menu 5 Choose Do STI Test from the Measure menu The Calibration procedure will start automatically The TEF will start repeating a 500 Hz octave band fre quency response sweep and a dialog box will appear announcing that the Source Calibration procedure is starting After each sweep the dialog box is updated with current level at the talker loudspeaker The cycle time of this test is approximately one second Heasure testing Starting Source Calibration procedure Adjust until level is 61 at 1 meter 67 at 0 5 meter Current level is 75 0 Press Esc to continue Illustration 5 8 Source Calibration dialog box for setting level Sound Lab TDS Performing measurements STI RASTI 6 As you monitor the level on screen manually adjust the gain of the test amplifier until the value in the dialog box reads 61 67 for 1 2 meter test 7 After the correct level is attained press Escape to continue to the Equalization procedure A message box will appear with the message Testing Speaker EQ The TEF is running a standard frequency response test from 88 Hz to 11 3 kHz one half octave below 125 Hz and one half octave above 8 kHz and then stores the measured equalization value Note For all subsequent intelligibility tests keep the gain control of the test amplifier at the setting th
136. in time at which the signal originates AL ons he measured percentage of Articulation Loss of Consonants by a listener In TEF Articulation scores are measured as percent of articulation loss of consonants in speech 96 AL of 0 indicates perfect clarity and intelligibility with no loss of consonant understanding while 1096 and beyond is growing toward bad intelligibility and 1596 typically is the maximum loss acceptable A weighting see Weighted ambience Room acoustics early reflections and reverberation The audible sense of a room or environment surrounding a sound source ambient noise Background noise associated with a given environment Sound Lab TDS Glossary mi amplitude In TEF measurements the total summation of all sound energy over the total time of the measurement at all frequencies within the bandpass of the instrument The sound energy at a given frequency over the entire time of the measurement Amplitude can be measured as the sound pressure at a given instant of time at a given frequency Amplitude is the maximum value of a field quantity in space or time analyzer A device that divides a spectrum into a finite number of frequency bands and determines the relative magnitude of the energy in each band TEF analyzers combine the capabilities of a computer sweep oscillator an accurate quartz timing clock and a sweepable bandpass filter system to make TDS measurements This hardware coupled
137. irectory sub menu TDS File Clear Ail File Mame ALTAROOL ETC Title ETC Taken To Show Feedback Through Altar Mic User Name LJS JAB Date 07 28 1993 09 15 33 Location Coalbush Church South Bend IN Description Line 1 1 Second ETC Center At 2kHz Line 2 PCC 160 On Altar Used As Pick Up Mic Format Binary Save Illustration 4 5 Save as sub menu Save as Saves the current test data settings parameters and job description to the drive and directory selected in the Drive Dirsub menu Until you execute Save as test data is stored only in memory and will be erased if a new measurement is performed 4 4 Sound Lab TDS File Menu Information that appears in the Save as sub menu is carried over from the last measurement re called file or configuration file The choices in the Save as sub menu are Clear All Erases all the entries made in the Save As sub menu and changes the file name to noname Additional data such as test Title User Name and Date and Location of the measurement are optional The Date is entered automatically by Sound Lab but you may change it You may also enter two lines to describe the measurement under Description Format allows you to save files in binary or ASCII file format Each file format has advantages and disadvantages A binary file takes up less space on the disk and is faster to open and display Itis not portable to spreadsheets e ASCII data requires several
138. is usually allows reflections into the measurement So for acoustic measurements you will generally set the time frequency resolutions to reject any reflections G5 G 6 Sound Lab TDS Best resolution and the TEF Resolution V mt For electronic measurements frequency responses of equalizers loudspeaker impedances etc you will almost always want to use Best Frequency Resolution You always want the Best Frequency Resolution you can get In acoustic measurements we are limited by the arrival of reflections In electronic measurements the are no reflections Now we can turn Best Frequency Resolution on and set the sweep time to get the frequency resolution that we want This way we get the desired frequency resolution with the shortest possible sweep time One final note on sweep rate and bandwidth The current values are always shown at the bottom of the Frequency Parameters menu You can set them manually if you want to There really is no reason to do so however What we are really interested in is the time frequency resolutian that results from the sweep rate and bandwidth Set the sweep time and resolution that you want and let the computer do the work of setting the sweep rate and bandwidth i Sound Lab Bibliography mi Bibliography The following bibliography references materials on the subjects of acoustics measurement time delay spectrometry perception and recording techniques Glen M Ballou ed
139. ise tests STI RASTI intelligibility tests and 3D tests Many options for display of the data are easily accessed from the Display menu To make Sound Lab TDS tests This section of the manual reviews the basic steps for making Sound Lab TDS measurements Before you attempt these measurements be sure you are thoroughly familiar with Section 3 Navigation which details how to navigate around the program work with menus and enter parameters For more details about the software and setting parameters see Section 4 Menus 9 1 Sound Lab DS Performing measurements Time and Frequency Response To make Sound Lab TDS measurements you may need an MS DOS based computer a TEF 20 analyzer Sound Lab TDS software an amplifier a speaker a tripod and a high quality microphone An alternative to using a microphone is a sound level meter with a line level output See TEF System 20 Analyzer User s Manual for hardware details Performing a time response test on a loudspeaker 1 Connect the system as described in the TEF 20 Analyzer User s Manual Put the loudspeaker and microphone on stands several feet from any reflective surface Put the microphone 1 meter from the speaker on Speaker I axis On the TEF E n analyzer set the output level knob about 1 4 of the way up Set your power amplifier level control about 1 2 of the way up These low settings prevent a Ex TEF and loud burst of noise Amplifier Computer
140. line and it falls off rapidly with sound pressure levels below about 40 dB F 25 F 26 Sound Lab TDS Glossary 001 spectrum The distribution of effective sound pressures or intensities measured as a function of frequency in specified frequency bands the display of a signal in the frequency domain The output vs frequency of a sound source including the fundamental frequency and overtones speed of sound 1130 feet per second at 20 degrees centigrade specular reflections Mirrorlike reflections of sound from a flat surface Reflections that do not spread out speed of sound in air 1130 feet per second at 20 degrees centigrade speech reinforcement The use of a sound system in an environment to increase speech intelligibility or sound power level SPL See sound pressure level standing wave An apparently stationary waveform created by multiple reflections between opposite room surfaces At certain points along the standing wave the direct and reflected waves cancel and at other points the waves add together or reinforce each other These are sometimes called room modes start frequency The starting frequency of a sweep Traditionally noted in equations as F1 stop frequency The ending frequency of a sweep Traditionally noted in equations as F2 ee Sound Lab TDS Glossary STI Speech Transmission Index A single number that indicates the effect of a transmission system on spee
141. lled the peak amplitude The more intense the vibration the greater the pressure variations and the greater the peak amplitude The greater the amplitude the louder the sound A 4 Sound Lab TDS Basics of Sound til Frequency The sound source in this case the loudspeaker vibrates back and forth many times a second The number of cycles completed in one second is called the frequency The faster the speaker vibrates the higher the frequency of the sound Frequency is measured in hertz abbreviated Hz One Hertz equals one cycle per second The higher the frequency the higher the perceived pitch of the sound Low frequency tones say 100 Hz are low pitched high frequency tones say 10 000 Hz are high pitched Doubling the frequency raises the pitch one octave Wavelength When a sound wave travels through the air the physical distance from one peak compression to the next is called a wavelength This was shown in Illustration A 3 Low frequencies have long wavelengths several feet high frequencies have short wavelengths a few inches or less Phase and phase shift The phase of any point on the wave is its degree of progression in the cycle the beginning the peak the trough or anywhere in between Phase is measured in degrees with 360 degrees being one complete cycle The beginning of a wave is 0 degrees the first peak is 90 degrees 1 4 cycle and the end is 360 degrees J Sound Lab
142. ly in terms of volts and seconds bd e MA IERI EIS nian pepe neta vie aaa as einn prc M ane ei Uds Vendee To calibrate the display select Input Calibration and enter the values shown in Illustration 6 3 The Reference Unit will r flect the units entered in the edit field i e pascals The Volts Per Reference Unit value is different for each microphone Please see your microphone data sheet for the correct value The Zero dB Reference Value of 00002 will calibrate the display for sound pressure level The default for the Propagation Speedis 1130 Changing the Distance Unit will update the propagation speed accordingly gt Close the Calibration and Input menu return to the Main menu C Illustration 6 4 Setting parameters for Time Response test Sound Lab TDS Practice measurements Setting the parameters for the Time Response test gt Go to Parameters menu and select Time MORES ETC Enter the following settings Paraneters Tine Response ETC Start Frequency Stop Frequency Center Frequency Frequency Span Sweep Tine Receive Delay Tine pan Humber of Sanples The center frequency will be automatically set by the computer when you select the startand stop frequencies The time span will be automatically set by the number of samples Note The time span of 22 2 milliseconds means that the display following the Time Response test will read from 0 millesceonds on the left e
143. move the cursor to the second peak and read the relative values in the cursor data window Paraneters Display Input a vi i J Q E D gt Q i Practice measurements Mil We can confirm this by placing absorptive material on the table top between the speaker and microphone press F5to repeat the test Gl xe TO RR m s Ku You should note a drop in di level of the second arrival Our test as shown in Illustration 6 9 showed the new level to be 523 6 dB verifying that the peak was caused by a reflection off the table top E led e Cam AAPL TUI Some other things we see in this display are two small peaks one 56 3 dB high at 5 78 feet and a 53 3 dB TIME tril bLiseconds gt FILE Tim ere Start Fred 200 0 stop Fraa 100 0 peakat6 13 feet By looking at our physical set up again there is nothing closer than the table top Therefore it appears that they are caused by reflections inside the speaker box Illustration 6 9 Measurement performed with sound absorptive material on the reflection gt Press F2a second time to turn the cursor off We are now ready to do a Frequency Response test 6 14 _ Sound Lab TDS Practice measurements mill Doing a Frequency Response Test TDS The Frequency response test shows how the output of a device is related to a frequency range of interest for a given amount of time It is displayed on a graph wit
144. mplex data real and imaginary is averaged for corresponding points in the multiple sweeps Use vector averaging for improved signal to noise ratio This improvement is somewhat reduced if the signal moves in time due to air currents Magnitude averaging With magnitude averaging the magnitude of the complex data real and imaginary is averaged for corresponding points in the multiple sweeps Magnitude averaging is useful for finding an average sound level for a region of the room when the microphone placed in several locations and then moved between sweeps Sound Lab TDS Parameters Menu Output The options under Output enable you to command the TEF to generate Pink or White Noise or a Sine Wave Tone up to 24000 Hz Pink Noise is activated by choosing the Pink Noise option White Noise is activated by choosing the White Noise option To specify a frequency for the Sine Wave Tone choose Frequency and enter a value for Hz When you choose Sine Wave Tone the tone will be heard The Enterkey will toggle on and off any of the selected options Paraneters Tine Response CETE gt Frequency Response TDS Noise Test NC STI RASTI cSTI gt 3D Test 3D Averaging Output Pink Noise White Noise Sine Wave Tone Frequency Illustration 4 20 The Output section of the Parameters menu 4 39 Sound Lab DS Display Menu mu Display pull down menu In the Display menu you control the way data is displayed
145. n and frequency resolution It will also produce a 3D with a smoother appearance A good starting overlap ratio for loudspeaker mea surements is 5 to 1 That 9 31 9 32 Sound Lab TDS Performing measurements Introducing 3D ail NES o no Lim e Mal MY I QR i LE f asas de Illustration 5 18 A 3D display witb low time resolution and bigb frequency resolution It sbows good frequency detail but very little time information i L Illustration 5 19 A 3D display with excess time resolution There is excellent time resolution but very little frequency detail Sound Lab TDS Performing measurements Introducing 3D Illustration 5 20 A 3D display that shows a good compromise between the two previous examples In this measurement we cam see detail in botb time and frequency data 9 33 _ Sound Lab TDS Practice measurements mill Se Section 6 Practice measurements Two basic tests This section of the manual details the sequence necessary for making two fundamental TEF measurements in a typical setup and gives suggested Starting parameters The object of this section is to help you to design a simple experiment to produce these measurements and get typical displays on the screen For information on how to enter data or use the menus see the Menu section About the ETC Two fundamental TEF measurements in TDS are the Time Response ETC and the Frequency Re
146. n cause sizeable peaks and dips in the measured response due to phase interference with the direct sound For the peaks and dips caused by reflections to be less than 1 dB the reflected sound level should be more than 9 dB below the direct sound level at the output of the TEF s filter For example suppose you re measuring the rear 180 degree frequency response of a cardioid microphone If the rear sensitivity of the cardioid microphone is 20 B 13 B 14 Sound Lab TDS How TEF works dB relative to the on axis sensitivity then the reflected sound level should be at least 9 dB less or 29 dB relative to the direct sound level at the microphone for 1 dB accuracy The farther a reflective surface is from the center of the space window the more its reflections are attenuated by the tracking filter The table below shows reflection attenuation versus the distance of the reflective surface from the center of the space window Distance of surface Attenuation of to center space window reflection dB in number of space windows 1 2 2 2 13 7 3 02997 4 72 5 Inverse square law attenuation further reduces the level of reflections Thetable shows that for maximum accuracy reflective surfaces should be well outside the space window ellipsoid Sound Lab TDS How TEF works The relation between resolution frequency and space window is F C D where F is the resolution frequency in hertz C i
147. n the Communication sub menu Settings Calibration Communication Baud Hate Port 7600 a b C d e f g 288 n h 208 j 348 k 388 4 Select the HI Base address with the HI Base Address sub menu The address set on the HI computer board must match the address you select with the HI Base Address sub menu The manufacturer s setting for the base address is 308 To change these settings see the page reference above Illustration 4 53 HI Base Address sub menu Sound Lab DS Input Menu To use parallel port communication To use the parallel port be sure the parallel cable is connected to your computer and simply choose LPT1 or LPTZ to match the port connection on your computer Settings E Calibration Communication Baud Hate 37600 LPTA X Illustration 4 54 Sub menu for selecting parallel communications 4 83 Section 5 Sound Lab TDS Performing measurements Time and Frequency Response mt Performing measurements Introduction Sound Lab TDS software combines with the TEF analyzer and your computer to form a complete measurement system The TEF analyzer generates a signal into a device or environment under test and then retrieves analyzes and visually displays the many Time Energy and Frequency relationships of the associated data Sound Lab performs traditional measurements such asthetime and frequency response No
148. n time by a constant amount When all of the individual sweeps are displayed on the screen they form a three dimensional display that plots the changes in magnitude frequency over time Do Average repeats from 2 999 tests and displays a the vector or magnitude average of Time or Frequency Response measurements Signal averaging is used to improve signal to noise ratios under adverse conditions such as noise Note You can cause an Auto Repeat mode for any Time Frequency or Noise Test by pressing the Function key F10 The test will repeat until you press Esc to cancel it A logical test sequence in a room for time and frequency measurements 1 Make a coarse Time Response Test one second span to reveal energy arrival times at the microphone Refine the time resolution 0 1 to 0 5 second time span if the first reading is too coarse for clarity Turn the cursor On and pinpoint the exact time of the first energy arrival at the micro phone Do a Frequency Response Test using a receive delay which equals the arrival time from the Time response 4 13 Sound Lab TDS Parameters Menu qu Parameters menu setting test parameters The commands in the Parameters menu determine the settings the TEF uses to make a test After the test changing any parameters removes test results from memory and erases the screen when the menu closes Use Alt Undo to retain parameters and not lose data Noise Test NC
149. nd can only be expressed in two w key words There is currently no support for DDOUBLE SINGLE DDOUBLE 1023 This is a zero based count Data count is always equal to Number of samples 1 7 705387e 7 3 902605e 6 2 588463e 6 Analyzer settings Summary table Noise data ETC1 header EIC1 data EIC 7 beader ETC7 data Illustration E 10 The blocks of the STI ASCII file format Sound Lab TDS File formats mi STI and HASTI file formats STI and RASTI files are composed of several blocks of data Some of the blocks contain header information and some contain data STI analyzer settings block Both RASTI and STI measurements store a record of all analyzer hardware settings in the analyzer settings block Also included in the settings block are operator comments test location and the date the test was made These settings are common between the NC and ETC measurements The settings block has 14 lines STI summary table block The summary table block contains the column headings for the STI display as well as the values for the display An ASCII tab chasacter hexadecimal 09 separates the columns If the measurement is an STI or NOISELESS_STT the display block will contain data for all seven frequency bands Ifthe measurement was a RASTT or NOISELESS RASTI measurement only two bands of data will appear in the summary table block E 13 E 1
150. nd the cursor status has changed or when test parameters have changed Cursors are not visible when the screen data does not match the test parameters Delay before test seconds The amount of time that remains before the test begins Disk error Path was not found Check the validity of the entries under drive and directory Drive was not found Check the validity of the entries under drive and directory Sound Lab TDS On screen messages il Disk is write protected Remove write protection Drive is not ready Be sure disk is in drive Write fault Possibly a bad disk or a faulty disk drive Disk is full Change disks or delete files Doing Noise Test 63 8000 Hz This message appears during an NC test and the NC portion of STI and RASTI measurements Drive not ready or illegal file information Check under drive and directory to see that drive and path are correct Is there a disk in the drive Error file was not saved Most likely there was no file name entered Use Save AS 7 Error in data file There is an error on a parameter value This error should never occur but if it does exit the program and begin again Error writing data file There was an error in writing to disk The disk may be full or not available D 3 D 4 c t ag a m Q or 0 On screen messages Insufficient disk space A Not enough space on disk Change disks or delete some files Invalid path Check
151. ne is precisely the same distance from the acoustic origins of both drivers the signals from each of the two drivers will arrive at the microphone at slightly different times requiring two different receive delay settings for each of the drivers individually 6 21 Sound Lab DS Practice measurements qh Illustration 6 15 ros MEE 0 Measure Parameters Display Input Frequency pbase response ites SSeS Se a i HERR EXER OU data with the receive Aiiiitid i delay entered directly Pea Raa baa EE Era El from the ETC at 4 91 JE EM EA EME A milliseconds The upward VID LYON slope of the phase data indicates tbe delay is set eli rcartilgiria4 43 past tbe correct time Le J PUL ET EA es Ll I o As p bt A a ge h AMPLITUDE cil if ai 3 f n 5 gt gt i t a a HARF Dent 5 8 5 8 a a BR 8 2 R E a FREQUENCY Hz Dist Res 4 0 Freq Res 1130 0 o a Oo 6 6 8 8 20 30 4000 5000 6000 7000 11000 13000 FILE TIM1 TDS IRE Oe v eee dll a Frequency pbase response MESS NUTREN set 0 1 millisecond earlier aora Pia ad baa REDS ano DEE as ba REN ue ars ENSE SEEN OR ERES entered into tbe parameters from tbe information box Tbe peje dal Pra pea downward slope of the an o ERED EREN phase data indicates that MEET e the setting was too far INE before the correct time ince FILE TIMa TDS O 1 0 Frea Res 1130 0 PHARF Mew APPLITUOE cup
152. nent information to report the status of a process or calculation is presented in windows called message boxes Message boxes contain information only They typically appear at the top center of the screen under the main menu bar Moving from module to module TDS File Open Old Drive amp Dir Shift F3 Save as Erase Configuration Printer Settings Print About ATA RTADEHO PrecisionEQ SLX Illustration 3 8 Go to sub menu Sound Lab software is comprised of several modules that make up a total measurement package When you start Sound Lab TDS for the first time the TDS module is loaded You choose other modules with the Gotocommand in File menu As you install new modules they will appear in the Go fo sub menu Sound Lab TDS File Menu TI Section 4 Menus for the TDS module TDS Drive amp Dir Save as Sshift F3 Erase Configuration Printer Settings Print About Go to Quit File menu Sound Lab communicates with disk drives and printers and accesses other modules under the Filemenu Four commands Open Old Drive amp Dir Save As and Erase perform tasks for data storage retrieval and path navigation Configuration provides a way to load save and erase configuration files Printer Settings and Print print the data on the printer About displays the current version of the software and if you are connected to the TEF analyzer will show the EE and
153. ng to a measurement made through a filter with a certain specified frequency response An A weighted measurement is taken through a filter that simulates the frequency response of the human ear at low levels C t Sound Lab TDS Best Resolution and the TEF resolution V mit Appendix G Best Frequency Resolution and the TEF Resolution V Farrel M Becker Turning on Best Frequency Resolution in the TDS module s Frequency Parameters menu causes the computer to automatically set the TDS parameters such that your measurements will always have the best possible frequency resolution for the sweep time that you have selected The longer the sweep time the better the frequency resolution will be To understand why this is so let s review some terms and then look at what we call the TEF Resolution V The frequency resolution of a measurement determines thelowest frequency that we can measure with accuracy as well as bow much detail we can see A lower number yields better resolution If we make a measurement with a frequency resolution of 1000 Hz then any feature a notch or bump that is less than 1000 Hz wide will not be fully resolved We will not see it accurately It may still show up but it may appear smoother than it really is If we change the frequency resolution to 500 Hz lower number therefore better resolution we will get a clearer image Rememberthat as we increase the frequency resolution smaller numb
154. ns Since such reflections will be perceived as direct sound you must include them in the direct sound portion of the calculation To do this Place the Dcursor on 66 54 one point to the right of the reflections The ALcons in the ALcons information box reads ROF If no strong reflections are present Place the Dcursor one point to the right of the direct sound and read the ALcons File Measure Parameters Display Input EUN 0 IRT6EO 0 58 Sec sec EDir ERev 0 4 dB 0 4 dB lyALcons 3 37 3 37 arsons ger Lam aoum sm MAGNITUDE lt dB gt C 0 48 H 192 75 p o m E 5 e D 66 54 N t5 in TOS Delau 3D Start Delay 3D End Delay FILE SNCTONLY ETC TIME milliseconds Start Freg 1782 0 Stop Freq 2218 0 Illustration 6 24 Finding tbe 96ALcows Sound Lab TDS Basics of Sound Appendix A Basics of sound Waves To produce sound something vibrates against air molecules which pick up the vibration and pass it along as sound waves When these vibrations strike our ears we hear sound Let s examine how sound waves are created Suppose a speaker cone in a guitar amp is vibrating moving rapidly in and out When the cone moves out it pushes the adjacent air molecules closer together This forms WAVELEN GTH idi ann i mad e did SEM ESSEN e 06096 0960900000000 0 O O 0600000000009 e e 9 00 0960000000 OO 0 6 O O O 6009000000000 9 O o O
155. ob description printing 4 3 K Keyboard test sequencing 4 34 L Lden F 12 Ldn F 12 Leq F 12 level F 13 Line Output Noise Test 4 27 Linear regression line RT 60 6 29 linear scale 4 48 liveness F 13 Ln F 13 logarithmic scale 4 48 Loopback 4 74 loudspeakers measuring 5 28 lowpass filter F 13 index 5 M Magnitude See also Frequency response magnitude Averaging 4 38 Measure menu 4 11 Do 3D Test 4 13 Do Average 4 13 Do Frequency Test 4 11 Do Noise Test 4 11 Do RASTI Test 4 12 Do STI Test 4 12 Do Time Test 4 11 Measure Noise STI RASTI 4 29 Measurements 3D 5 28 ALcons 6 25 first time 6 1 Frequency Response 5 6 RT60 6 25 STI RASTI 5 15 Time response 5 2 two port F 29 menu title selecting 3 3 Menus Display 4 41 File 4 1 Input 4 74 Measure 4 11 Parameters 4 15 Message boxes 3 8 Messages Awaiting the Trigger D 1 Bandwidth D 1 index 6 Sound Lab TDS Index Can not save 1 D 1 Can t difference D 1 Check communications D 2 Cursor is off D 2 Delay before test seconds D 2 Disk error D 2 Doing noise test D 3 Drive not ready D 3 Error file D 3 Error in data file D 3 Error writing D 3 Files not found D 5 Insufficient disk space D 4 Invalid path D 4 Loading D 4 Measure halted D 4 Measurement interrupted D 4 Min 0 Max 60 D 4 No data available D 6 No data current D 5 Not enough memory D 6 Obtain STI data D 5 Parameters changed D 7 Path filename
156. oduction to Professional Recording by Bruce Bartlett 1987 TECHRON is a division of Crown International Inc 1718 West Mishawaka Road Elkhart Indiana 46517 4095 E Dedication Sound Lab Foreword mi It is the theory which decides what we can observe In 1967 a remarkable man Richard Heyser brought a new paradigm to the science of sound His passion for the study of acoustics sound perception and audio measurement launched him upon a solitary journey in uncharted areas between paradoxes in the understanding of sound His travels led from one end of the spectrum of language and thought to the extreme opposite Here was the problem Things don t always sound the way they measure While statistical excellence could be described in the symbolic language of objective analysis it was often contradicted by the language descriptions of subjective perception And it was in this world of paradox that Dick Heyser navigated comfortably until he found an entirely new world emerging on the horizon The expansive Heyser often quoted Einstein It is the theory which decides what we can observe From the center of that theory Heyser began to push into new horizons of sound measurement unrestricted by the boundaries of convention Along the way his observations drawn from nature itself fueled his thinking into even deeper areas of understanding with far reaching implications He generously shared
157. oduction to Sound Lab TDS What you purchased what you need know equipment you need and where to get help Section 2 Installing Sound Lab TDS Step by step instructions to install Sound Lab TDS on your computer Wy Sound Lab TDS Introduction mi Section 3 Navigation in Sound Lab TDS How to move around in Sound Lab TDS Explains menus important keys and moving around within the program and from module to module Section 4 Menus for the TDS module These menus are detailed File Measure Parameters Display and Input Section 5 Performing measurements This section of the manual details the sequence used to make time and frequency response tests noise tests STI RASTI tests and 3D tests Section 6 Practice measurements A practice measurement session you can set up to perform the most fundamental TEF measurements time response and frequency response Explanation and exercise on cursor functions for 96 ALcons and RT60 calculations Appendix A Basics of sound Fundamental acoustic principles and basic concepts you need to know to understand TEF measurements Appendix B How the TEF analyzer works This section describes how the TEF analyzer works discusses the relationship between time and frequency measurement resolution the interrelated parameters and space window considerations Appendix C Data interpretation Described and explained are several tests to help determine the legitimacy of a measurement
158. olume 13 Stroudsburg Pennsylvania Dowden Hutchinson amp Ross Inc 1979 symbols more 4 2 3D CWaterfall Auto Scaling 4 55 Bottom of Scale 4 55 Curve order 4 55 display 4 43 measurements 5 27 Parameters 4 30 Perspective 4 55 Top of Scale 4 55 3D End Delay cursor button 6 29 3D Start Delay cursor button 6 29 A About 4 1 4 9 acoustic center origin F 1 action buttons 3 7 Add Noise to STI RASTI 4 59 Adjust colors 4 66 Alcons 6 25 definition F 3 measuring with ETC 6 34 setting the cursor 6 30 Alt Beep 4 72 Alt Brief 4 3 Alt Close 3 7 4 3 Alt Full 4 3 Alt Info 4 3 Sound Lab TDS Index ail Index Alt Mouse 4 72 Alt Print 4 3 AltUndo 3 7 4 15 ambient noise F 1 amplitude peak F 15 analyzer F 2 anechoic F 3 Arrow keys 3 2 articulation loss of consonants See ALcons ASCII 3D file format E 25 ETC file format E 2 NC ASCII files E 6 RASTI file format E 13 Saving TDS files as 4 5 TDS file format E 9 attenuate F 3 Auto Repeat 4 13 Auto Scaling 4 45 4 69 3D Waterfall 4 55 Frequency Response 4 48 4 49 4 50 4 51 Time Response 4 44 Average 4 13 Averaging Magnitude 4 38 Measurement type 4 36 Number of Sweeps 4 36 Pause Between Sweeps 4 36 Test Sequencing 4 37 Vector 4 38 index 1 B Back to Front 3D 4 56 4 71 band pass filter F 3 Bandwidth GD 4 32 TDS 4 22 4 25 definition F 3 Optimum 4 21 sweep rate B 10 Base address 4 82 Baud Rate 4 81 Best Frequency Resolution G
159. on B 2 If the filter bandwidth is sufficiently narrow the reflection is rejected or filtered out No reflection signals are received by the TDS analyzer In other words an anechoic measurement is made in an ordinary room Sound Lab TDS How TEF works mil Reflecting E surface Reflected sound 800 Hz 15 Microphone Speaker pac gt Nd 1000 Hz Direct path Direct 1000 Hz s sound only Tracking filter Illustration B 2 A reflection is filtered out of a TEF measurement Helationship between Time Frequency Any method used to measure frequency requires a time interval in which to measure it For example if we want to describe the motion of a pendulum we might say that the pendulum swings from right to left and back again in 1 2 second That is it has a period of time of 1 2 second This is a description in the time domain Alternatively we might say that the pendulum moves from right to left and back again with a frequency of 2 Hz Q cycles per second This is a description in the frequency domain Both are correct and each is required to measure the other A time interval is required to measure frequency regardless of the measuring method used B 3 B 4 Sound Lab TDS How TEF works nil Fourier transform Frequency information is mapped into time information by means of a calculation called the Fourier transform The Fourier transform relates time and frequency for TEF s sweeping oscillator T
160. ook at what goes on as you change the bandwidth of the filter Sound Lab TDS Best Resolution and the TEF resolution V In Illustration G 1 the TEF Resolution V is a graph in the shape of the letter V that shows how the frequency and time resolutions vary with the bandwidth of the sweeping filter and a fixed sweep rate The vertical scale of the graph shows frequency resolution in Hz on the left side and time resolution in seconds on the right side The horizontal scale is the bandwidth of the filter Note that the horizontal scale is logarithmic This is done so the V shaped curve will appear to be symmetric about the center of the graph The bandwidth at the center of the horizontal scale is equal to the square root of the sweep rate and is marked Sqrt SR This particular graph uses a sweep rate of 10 000 Hz s Therefore the bandwidth at the center of the horizontal scale is 100 Hz the square root of 10 000 Bandwidth values to the left of center are less than the square root of the sweep rate and values to the right are greater ge o Time Resolution sec E E E G Em S a m i E i Li ha lt Sqrt SR gt Sqrt SR IF Bandwidth log scale Illustration G 1 The TEF Resolution V G 3 G 4 Sound Lab TDS Best resolution and the F Resolution V il The frequency resolution is shown by the V shaped curve marked Rf that starts in the upper left corner curves down
161. or data windows 989 2220 0 C Illustration 4 44 Relative cursor Sound Lab TDS Display Menu ml Other Display options Relative cursor The relative cursor mode is available for both the time and frequency cursors The relative cursor is used to find curve data values relative to a reference point on the curve To use the relative cursor first turn the cursor on and position the it on the point you want to designate as the reference point Select the relative button at the bottom of the screen click on it or press R to make this the reference point As you move the cursor you will note that a phantom cursor is left behind at the reference point and the cursor values are now referenced to that point For example if the cursor is on a data point that is 10 dB below and 100 Hz to the right of the reference point the value in its data window will read 10 dB and 100 Hz If you choose the Units cursor button the cursor data window will show the magnitude in your chosen Reference Units as set in the Inpit Calibration sub menu reference point q 20 dB Fo di cursor buttons lo x 400 Hz TY 4 65 Information boxes TDS Sound Lab TDS Display Menu TIT RT6O cursor The RT60 cursor is toggled on or off The Sbift F2 key also activates the RT60 cursor When the RT60 cursor is On Sound Lab performs an integration on the time response data and displays it in a second color Th
162. ost likely it is not When you see something like this your first thought should be What did I do wrong In the above example you would probably start looking for a source of 60 Hz hum in your measurement setup If you have checked and double checked and are convinced that your measurement is correct it probably is However it should take a lot of convincing to believe that a 4 inch loudspeaker is putting out large amounts of 60 Hz C 1 Sound Lab TDS Data Interpretation mi Is it repeatable One test that can and should be made to determine the legitimacy of a measurement is to check its repeatability You should be able to recreate and repeat a valid measurement of a real phenomenon with the same results each time The TEF Analyzer provides a very handy tool for checking the repeatability of a measurement the Difference mode To check a measurement that you have just made turn on the Difference mode and repeat the measurement If it is repeatable the difference should show virtually no variation between the two measurements Illustration C 1 is a difference with poor repeatability There are variations of over 6 dB across the entire screen A E e A f eurer EN O ee ed is nee id de AMPLITUDE dB a ee eee eee ee ee ae ee ee ee eee bee Merz pe eee ee n a n MODE DIFF TIME HilliSecs gt Illustration C 1 A difference with poor repeatability Sound Lab TDS Data Interpretation mil
163. p a f 2 wa LM bam rs ie T E POLA ET VM gt y If MAY TELLS LEE ae EI E E nifi c Illustration 4 32 AN e H Electrical impedance of a two FM Lx way speaker a a E tt a T ei A in s a A E c E inn oo ald a P A AEF Illustration 4 33 Electrical impedance of a 20 microfarad capacitor es z BRACI Hisl Y es A T a D E a a ae a i eie tete Ext 1 e E 1 ES EU Sa re AE Illustration 4 34 Electrical impedance of an 8 obm resistor 4 54 Sound Lab TDS Display Menu itl Display options 3D Waterfall The 3D display shows frequency response curves vs time in successive time slices Each curve is offset slightly from the previous one in the same display The parameters that can affect the 3D display are Perspective Curve Order Top of Scale Bottom of Scale Auto Scaling Horizontal Scale Display Time Response ETC Frequency Response TDS gt 3D Waterfail 3D gt Right Curve Order Front to Back Top of Scale 100 dB Bottom of Scale dB Auto Scaling Horizontal cale amie Illustration 4 35 The Display 3D Waterfall submenu 4 55 4 56 Sound Lab TDS Display Menu mm Perspective Toggles between Left and Right views of the display When viewed from the left perspective the lower frequencies are nearest you when viewed from the right perspective the higher frequencies are nearest you Curve Order Toggles between
164. p rate When making measurements with Sound Lab you set the desired time distance and frequency resolutions in the Parameters menu The TEF will then set the combination of sweep rate and bandwidth of the tracking filter accordingly While sweep rate and bandwidth can be set manually it is easiest to set a frequency resolution and a sweep time and let the computer automatically set the sweep rate and bandwidth for you There are an unlimited number of combinations of sweep rate and bandwidth that will result in a given set of resolutions The choice should be governed by the environment noise levels because as the bandwidth is narrowed the probability of interference is reduced Slower sweep rates mean less bandwidth in the tracking filter thus less noise getting into the measurement With a slower sweep rate greater total energy is put into the test creating improved signal to noise ratio As bandwidth is reduced and resolution remains fixed the time to take the measurement is increased because Sound Lab will change the sweep time to keep the parameters valid If the testing environment is relatively free of noise fast sweeps can be used If noise is a problem slow sweeps should be used Sound Lab TDS How TEF works till This capability is one of TEF s greatest advantages over other systems When there is little noise present you can sweep very rapidly and measure from 0 Hz to 20 kHz in less than one second If there i
165. pears to rise as it passes and moves away it appears to drop Sound Lab TDS Glossary il doubling A special effect in which a signal is combined with its 15 to 35 millisecond delayed replica This process mimics the sound of two identical voices or instruments playing in unison early decay time The time for a sound to decay 10 dB from its original level Short decay times cause music and speech to sound dry or muffled Long decay times make speech unintelligible and difficult to understand It is the figure that most closely approximates how the decay time sounds to the ear early sound early reflections Sound arriving within about 70 milliseconds of the direct sound echo A sound wave which has been reflected or otherwise returned with sufficient magnitude and delay to be pereeived as distinct from that directly transmitted Echoes are perceived as distinct repetitions of the original sound A sound delayed 90 milliseconds or more combined with the orginal sound is sometimes considered an echo EFC Energy Frequency Curve A Frequency Response A snapshot of all the energy returned in the frequency range of interest for a given amount of time Frequency is displayed on the horizontal axis magnitude on the vertical axis ellipsoid a three dimensional ellipse In TDS the football shaped space around the loudspeaker and microphone corresponding to points at which the TEF test tone is attenuated by 3 dB
166. play colors a b c d e f a h i j k l m n o Fs Illustration 4 47 4 68 Sound Lab display colors Sound Lab TDS Display Menu hil Summary of Display menu options Top of Scale The 7op of Scale value in dB determines the value that will be displayed at the top of the vertical scale Bottom of Scale The Bottom of Scale value in dB determines the value that will be displayed at the bottom of the vertical scale Auto Scaling Toggle Auto Scaling on or off If Auto Scaling is On the TEF will automatically scale the data to display the full magnitude range of the measurement The highest data value is placed in the top 10 dB of the graph and the scale annotation is adjusted accordingly The new Top of Scale and Bottom of Scale will be updated when the data is redisplayed Manually entering a value for Top of Scale or Bottom of Scale automatically toggles Auto Scaling Off We recommend that Auto Scaling be left on for most measurement tasks If Auto Scaling is off and all the data is out of the selected range you will not see any data on the screen 4 69 470 Sound Lab TD Display Menu ail Auto Scaling can be toggled off if you don t want the graph s Top of Scale value to change with data level from test to test This is a requirement if you are going to use Overlayto create a family of curves on the screen resulting from several tests See additional comments in Overlay command
167. ra NANA E 1 E er E E LL ioo E 2 AISNE TES AGI Rn tnnt c ed b an cima creat a E 2 The ETC dAd oisein PEENI EATE i E ON E A E 2 Do SINS SEU CEES derroto E 3 NS A DTE D E 6 Hs A On ec dtm i ous Feo dempta E 6 Hiver NTC COELO i sath A a I R E 6 Notes ORIGIN CANES masa sn costi E 7 The TDS header The TDS data STI and RASTI file formats STI ETC header block Notes on STI summary table block Notes on STI noise data block T Notes on STI ETC block eee 3D file format Appendix F Glossary INGLES OR MDS SISSE LE STI analyzer settings block ssss STI summary table block eL ow 8 9OR OB 3 9 ZR OB OW AA AAA Y ROW Ro ON VW B RON OR OW STL ETC data leaks tttm cee The 3D master file header eese Notes on 3D fes uo a aa Sound Lab Contents till Appendix G Best Frequency Hesolution and the TEF Resolution V Bibliography vi Nee Section 1 Sound Lab TDS Introduction mi Introduction Sound Lab TDS uses the measurement technique of Time Delay Spectrometry TDS to make Time Energy and Frequency TEF measurements Time Delay Spectrometry is a time selective measuring technique suited to making transfer function measurements on devices that have a well defined input and output TDS falls into the general class of two port measurement methods where the test system generates a test signal sends th
168. re more evident Adjusting the receive delay to tune in to the phase The phase display is a most sensitive time measurement remember that phase is both time and frequency dependent When measuring phase the correct Receive Delay is critical We see that the phase display slopes upward from left to right This slope is the signature of excessive receive delay Although in the previous test we had set the filter to compensate for this delay with the ETC cursor that setting is only near the correct delay Sound Lab TDS allows you to use phase data for precise adjustment of the receive delay an accurate way to determine if you are aligned to the acoustic origin of a speaker A correct delay would be shown in the phase signature as relatively flat in those areas where the magnitude curve is relatively flat A slope to the left or right would indicate that the delay is imprecisely set You could re open the Parameters Frequency Response menu and manually experiment with different receive delays to get the desired results Sound Lab TDS offers a quick way to do this _ Sound Lab TDS Practice measurements mi TDS Measure Paraneters Display Input Changes Delete Current Data 180 TDS Receive Delay Ge es 0 0 Laso Alt Close wee 90 e 60 g A v 30 a m a 5 n0 E 7 q 5 30 I E t 60 90 120 150 50 3 ia z i 1 H H H H H i E r i E i 180 aa a o c O Oo ao O O o O s co o o tO O Oo 5 E S So te Di
169. ree cursors can then be moved across the data to process RT60 calculations and a ALcons calculation Sound Lab displays the RT60 the direct to reverberant ratio the ALcons and the difference in level between the left and right cursors on the integrated curve File Heasure Parameters Displau Input gt RAT60 0 94 Sec EDir ERev 6 8 dB ALcons 5 69 dB down 10 1 60 H y T 1 T 7 T Y Id f TEF 9 zu 40 AM PE ai 30 LAA IEA Lue eiecit az I 3 20 fre TMi ty u Jd I a ag iHi T 10 Las E 5 0 einem Cursor data D a ppi MU a a aaa am E T A windows aloes E a M n LE 70 Li 30 02 _ in Hp ar p 2 n nmn p m lb 56 84 a 5 8 ls 5 E TOS Delay SD Start Delay Start Freq 1730 0 Stop Freq 2220 0 4 56 Illustration 4 45 Time response ETC display witb RT60 cursors active Sound Lab TDS Display Menu il As the active cursor moves across the screen each of these values is updated All three cursors can be manipulated with mouse or the Arrow keys On the ETC TET the cursors select L Left end of the RT60 computation D Division between the early and late sound used in the calculation of early to late energy ratio for a V ALcons measurement EM R Right end of the RT60 computation The text in the data readout of the active cursor is a different color than the other two To select a different active cursor press the prefix letter CL D or B
170. response frequency F 10 impulse F 11 phase F 15 reverberation A 9 F 21 Reverberation time 6 26 A 11 F 19 room measuring with 3D 5 30 modes A 11 F 22 time F 22 root mean square F 22 RT60 6 31 6 32 F 19 calculation 6 35 cursor 4 66 4 72 cursor button Sound Lab TDS Index mil 3D End Delay 6 29 3D Start Delay 6 29 Slope 6 29 TDS delay 6 29 early decay time 6 28 early RT60 in STI 5 24 Linear regression line 6 29 measurements 6 26 out of range message D 7 Schroeder curve 6 28 setting the cursor 6 28 RT60 cursor is on off D 7 S Sabin F 22 Save 1 4 6 Save As 4 1 4 4 Schroeder integration 6 28 F 22 serial communication 4 81 Serial port 4 81 signal delay See receive delay sine wave F 23 Sine Wave Tone 4 39 SL directory 2 6 command tree 2 6 SL BAT 2 6 Slope cursor button 6 29 sone F 23 sound absorption F 23 decay F 23 definition F 23 discrete arrivals F 6 early F 7 intensity F 23 index H level F 24 near field F 13 power F 24 reverberant field F 21 speed of F 26 sound level meter F 24 Source Calibration STI RASTI space window B 12 B 14 F 24 See also ellipsoid span frequency F 10 Speaker EQ testing 5 17 specular reflections F 26 speech intelligibility F 25 Speech Transmission Index F 27 SPL F 24 Standard Transmission Class F 27 Standing waves A 12 F 26 Start Frequency 3D 4 30 ETC 4 16 TDS 4 20 Start Receive Delay 3D Tests 6 29 3D tests 5 28 5 30 SII F 27 abou
171. rf Sine Have Tone orr Frequency 1000 0 Hz Illustration 4 17 The STYRASTI parameters menu Measure Noise This choice is an On or Offtoggle Sound Lab provides the option to measure either with or without background noise Choose Offif you do not want the room noise included in the measurement If you measure without noise it can be entered later by choosing Add Noise to STI RASTI in the Display menu Source Calibration This choice is an On or Off toggle For correct speech intelligibility measurements the acoustic level of the source loudspeaker must be calibrated to simulate the actual level of human speech See Section 4 Measure menu for the complete source calibration Rene ets 4 29 4 30 Sound Lab TDS Parameters Menu mi Parameters 3D Test 3D The Parametersmenu for 3Dis similar to the parameters for the Frequency Response test The interactions among the following values of Start receive delay End Receive Delay No of Curvesand Receive Delay Step are shown in Table 4 4 a Tine Response ETC Frequency Response TDS gt Noise Test NC STI RASTI CSTI start Frequency 200 0 Hz Stop Frequencu 15000 0 Hz Sweep Tine 1 9 s Sweep Hate 7708 3 Hz s Resolution Frequency 300 0 Hz Distance 3 8 ft Tine 3 3333 ms Best Frequency Resolution On Start Receive Delay 0 0000 ms End Receive Delay 5 0000 ns Receive Delay Step 0 1389 ns Bandwidth ase 46 3 Hz Nusber of Sanples 312 Numb
172. ring STI calibration this indicates the automatic sweep for calibrating level has been stopped by the user Press Enterto proceed to the equalization test During ETC or TDS sweeps this indicates Escape was pressed Testing This message appears during a TEF sweep It is usually followed by Receiving Data gone Test Timed Out The PC did not receive the test data from the analyzes in the required amount of time See the Check Communications section found on previous pages of this section The printer is not ready check the printer and try again Be sure the cable is connected to the printer it is turned on on line and plugged in Sound Lab TDS On screen messages mn The TEF is not responding Reset the TEF and try again You have lost communications with the TEF Make sure the correct cable is connected and the communication settings are correct for the cable used and the hardware switch settings There is not data available to print Make a measurement or load data with Open Old before printing Time span should not exceed sweep time Reduce time span or increase sweep time YW Sound Lab TDS File formats hill Appendix E ASUII file formats TEF ASCII file formats consist of two or more blocks of information Usually these consist of a header block and a data block Information in both of these blocks is needed to process TEF data with spreadsheets and high level programs such as BASIC or Pascal
173. ront Of Balcony t On Main Floor E LI integration Ti me CRT UT orcos XM EM c in 8 Number of Samples means po cc NM Tate 9 Volts Per Reference E x 3 B 11 Preamp Gain A MB NUNG ANNECY RET Gain B 5 F E i i E f T E E I 1 A H 1 T gt Li T T r1 a iz a a E H 8 E r 1 1 7 a Illustration E 2 NC ASCI file displayed in a spreadsheet ee 1 6E 01 4 OOE 01 8 1 SE nt ui 0E DT mM e 22b 01 i HO OSE oi 1 53E 01 2 ai 3 5 E 0 cit 0 00 00 Seaman SOE OOF ee AM IES 1E es are not displayed by the spreadsheet seasan MONEE QU O CIA E The double quotes C Sound Lab TDS File formats TI TDS ASUII files The TDS header The first part of the TDS file is the header information The header is a record of all analyzer settings that went into making the test Also included in the header are operator comments test location and the date the test was made Line 31 the last line of the header is always Data The TDS data The second part of the TDS file is the collected data The data is stored as the voltage measured by the TEF independent of the preamp gain The number of lines in the data part of the file always equals the number of samples selected when the test was made 512 1024 2048 4096 or 8192 lines Each line consists of the following items e A real number in scientific notation Atab character hex
174. s EXCELLENT GOOD FAIR POOR AD C ALTARFB STI THT Sound Lab TDS File formats mi Illustration E 12 STI and RASTI summary table block E dni E 19 Sound Lab TDS File formats nil Notes on STI noise data block da Parameter label Value Comments NOISE DATA This is the key word for the start of the noise data summary The eight values are always shown regardless of whether a NOISELESS SIT or NOISELESS_RASTI measurement was performed If a NOISELESS_STI or NOISELESS_RASTI measurement was performed the values are expected to be all zero 0 000000e 0 If the measurement is a FULL_RASTI and the noise was not input from a table or from a NC file then element four and element six will be the only elements with values as shown below 1 70E 01 2 90E 01 3 50E 01 3 40E 01 3 00E 01 2 80E 01 2 40E 01 2 00E 01 Integration time Used only for RASTI Used only for RASTI The STI setting is always 4 for integration time If noise data was imported from an NC file this value will always fall between 1 and 9 999 E 20 Sound Lab TDS File formats ail RLTRRFB STI THT RRRARARRZSU A ERBSSARREBESRERBHSEZRSERHRSERGSRERERAARGRREBREZASRSEESNESGARRSU ETRRRHZSGRSERSNERESEERNENGXAR RSSCARSSREAGRRESENERERARRRREAXARNASREZERRRENEAGGRORR AR NN NN AA Le ts Start Frequency T
175. s 3D 4 33 Between Sweeps Averaging 4 36 peak amplitude F 15 percent ALcons See ALcons Performing FFT D 7 Perspective 3D 4 55 4 71 Phase See Frequency Response Phase cancellation F 16 definition F 15 interference F 16 relative F 19 shift F 16 Phase and phase shift A 4 Pink Noise 4 39 F 17 polar pattern F 17 polarity F 17 Port 4 81 post processing data F 17 pre delay F 17 Preamp Gain 4 75 precedence effect Print 4 1 4 8 Printer Graph Size 4 8 Resolution 4 8 Settings 4 1 4 8 printing job description 4 3 propagation F 18 Propagation Speed 4 77 4 79 6 6 F 17 index 8 Sound Lab TDS Index il pull down menu 3 1 Pulse trigger test sequencing 4 34 pure waveform F 18 Q Q F 18 Quick keys 3 2 Quit 49 H rarefaction F 19 RASTI converting to ALCONS 5 24 definition F 18 file format E 13 Receive Delay B 9 ETC 4 17 TDS 4 22 definition F 19 setting with phase 6 19 Start GD 4 31 Step 3D 4 32 5 30 Receiving Data D 7 Reference Unit 4 77 4 78 6 6 Reflections A 7 definition F 19 eliminating B 2 finding 6 12 focused F 8 refraction F 19 reinforcement speech F 26 relative cursor 4 65 6 12 relative phase F 19 required files 2 6 F 19 Resolution GD 4 31 Best Frequency 3D 4 31 TDS 4 25 Distance 3D 4 31 TDS 4 21 Frequency C 5 F 9 F 20 3D 4 31 TDS 4 21 measurement B 5 message D 7 printing 4 8 Time F 20 3D 4 31 TDS 4 21 resonance F 20
176. s When two sinusoidal signals of the exact same frequency track each other F 15 Sound Lab TDS Glossary mu exactly in time reaching their maximum minimum and zero values in synchronization they are said to be in phase If they are not synchronized then it is as if one signal is delayed with respect to the other and there is a phase difference Phase is measured in degrees or radians Phase is frequency and time dependent Phase measurements are the most precise indicators of alignment phase cancellation phase interference The cancellation of certain frequency components of a signal that occurs when the signal is combined with its delayed replica At certain frequencies the direct and delayed signals are of equal level and opposite phase 180 degrees out of phase and when combined they cancel out The result is a comb filter frequency response having a periodic series of peaks and dips Phase interference can occur between the signals of two microphones picking up the same source at different distances or can occur at a microphone picking up both a direct sound and its reflection from a nearby surface Phase cancellation also occurs when two time offset speaker drivers play the same frequency phase shift Phase difference in degrees of phase angle between corresponding points on two waves It is the fraction of a cycle by which one of the waves would have to be moved along the time axis to make the two waves coinci
177. s a high level of ambient noise you can slow the sweep thereby narrowing the bandwidth of the filter in order to maintain resolution and reject the noise The noise is rejected by the narrowness of the filter Very little of the noise signal is going to be present in a 2 Hz wide filter Measurement repeatability should be used as a criteria to select the highest reasonable sweep rate If the noise or sweep rate is too high the measurement will change from one sweep to the next The wider the bandwidth setting the greater the time window or range of time over which signals are accepted by the analyzer The relation between time window bandwidth and sweep rate is T B S where T width of time window in seconds B bandwidth in Hz and S sweep rate in Hz seconds Since sound travels a certain distance within a time interval the time window corresponds to a space or distance window The space window is an ellipsoid space around the speaker and microphone inside of which sound reflections are included in the B 11 B 12 Sound Lab TDS How TEF works TIT measurement The speaker and microphone are at the foci of the ellipsoid Sound reflections originating outside the space window are excluded from the measurement Actually they are attenuated 3 dB at the edge of the space window ellipsoid and by greater amounts outside that For example suppose you had a two millisecond time window Since sound tra
178. s the speed of sound in feet per second D is the space window in feet If we want to measure down to 100 Hz we need a space window of roughly 10 feet or a clear space 5 feet around the microphone and loudspeaker from the formula F C D Check that the path length of each room reflection exceeds the direct sound path by more than one wavelength of the lowest frequency to be measured Direct sound p space window 3 dB attenuation 3 dB attenuation amp Reflection 15 dB attenuation 15 dB attenuation SS SS eee Distance eem Two space windows Illustration B 5 The space window B 15 Sound Lab TDS Data Interpretation Appendix C Data interpretation Is it reasonable It has been said that in order to properly measure a device you must know all there is to know about it But if you already know all there is to know about it then why do you need to measure it Obviously when we measure something we don t know all there is to know about it That s why we are measuring it Because we don t know it all we must be careful when we measure We must convince ourselves that the results of our measurements are real and correct When interpreting the data presented by the TEF Analyzer Cor any measurement system for that matter you must always ask yourself Is this reasonable If you are measuring the low frequency response of a 4 inch loudspeaker and a huge bump appears at 60 Hz is this reasonable M
179. s with carrier frequencies on octave centers from 125 Hz to 8 kHz The carriers are modulated with speech modulation frequencies of 0 5 to 16 Hz at one third octave intervals These measurements result in a data set containing 98 modulation reduction indexes which are in turn converted into a single index called the Speech Transmission Index STD The STI value is a single number that indicates the effect of a transmission system on speech intelligibility An alternate method for computing the MTF measures the impulse response of a system without having to directly measure the modulation transfer characteristics at each individual modulation frequency This method derives the MTF by calculating the frequency spectrum of the squared impulse response of the system TDS measurements are a slightly modified version of the impulse response method Because the TDS process for the ETC measurement yields the complete analytic signal response both real and imaginary parts of the system under test this complete signal information is used to calculate the MTF 0 25 3 26 i J Q Q oO J 0 ME measurements STI RASTI ml Overall STI and RASTI values are derived by making MTF measurements at all the octave bands between 125 Hz and 8 kHz for STI and at only 500 Hz and 2 kHz for RASTI Illustration 5 15 Diagram A sbows a sinewave modulating random frequencies wbicb are characteristic of tbe buman voice This modulation
180. se Settings Calibration Pascal Volts Per Reference Unit 0 00226 Zero dB Reference Value 0 00002 Reference Unit Propagation Speed 1130 0 feet inches meters centimeter BT Illustration 4 51 Distance unit sub menu Sound Lab DS Input Menu mi Communication sub menu Use the Communication sub menu to match hardware and software settings for communication between the TEF and your PC Sound Lab lets you choose serial COMI or COM2 HI host interface or parallel communications LPT1 or LPT2 To use serial communication ze inue Calibration Communication Baud Hate 57600 COM1 Illustration 4 52 Setting sub menu 1 Set Baud Rate to match the serial interface settings made on the analyzer For more information see Section 5 in the TEF 20 Analyzer User s Manual 2 Connect the analyzer to a serial port connector designated as either COMI or COM2 on your PC See your computer installation manual for the location of COMI or COM2 One of these ports may be used for the mouse Make the same selection in the Commu nication sub menu 4 81 Sound Lab DS Input Menu To use HI host interface communication 1 Instructions for installing the HI PC card can be found in Section 5 Pages 5 7 to 5 9 in the TEF 20 Analyzer User s Manual 2 Connect the TEF analyzer to your PC with the cable that came with the HI PC card 3 Select HI i
181. se the MS DOS command Tree to confirm that the following files are in the SZ directory All of the files shown in the following illustration must be present but not necessarily in the order shown C DPMI16BI OVL TDS OVR TDS SL RTM EXE SL MNU SL COM TDS SET DATA Illustration 2 1 The directory tree after TDS installation C Mc Section 3 TOS Measure op will Eo E Illustration 3 1 Sound Lab TDS Navigation mil Navigation in Sound Lab Navigation in Sound Lab Sound Lab TDS software runs under DOS and uses a mouse input device and pull down menus and sub menus which contain either parameters or commands In this manual the terms command parameter option and item are used interchangeably to refer to menu selections The current Sound Lab TDS module name appears in the upper left hand corner along with the major menus in the Sound Lab TDS program File Measure Parameters Display andInput Pull down menu To Main Menu Bar a tun Sound Lab IDS you Parameters Display Input select one of the five menu titles from the main menu bar Sound Lab TDS then drops down the rest of the did menu displaying the list of items on the menu One or more sub menus allow you specify your instructions about test parameters down menu Main Menu bar 3 1 Sound Lab TDS Navigation mill Getting around Sound Lab TDS offers you three ways to navigate through the
182. sound decays into the noise 4 Set Time Resolution In the Parameters menu under 3D Test enter a value five times longer than the Receive Delay Step in small rooms and to the same value as the Receive Delay Step in Performing measurements Sound Lab TDS Introducing 3D large rooms The ratio of time resolution to the space between sweeps is called the over lap ratio As explained later these settings will give a smooth 3D display with good frequency and time resolution 5 Perform the measurement and examine the display If desired repeat the measurement with different parameters Overlap ratio in 3D displays For each offset in a 3D measurement a single TDS sweep is performed having a time window as oweep 4 Sweep a Sweep 6 2 3 4 5 6 T 36 Illustration 5 17 In this illustration the wide vertical lines represent the time offsets of the individual TDS sweeps The overlap ratio in 3D measurements refers to time resolution settings that are longer than the time spacing between curves In this example the time resolution of each sweep is three times longer than the spacing 37 determined by the sweep rate and IF bandwidth In most cases the time resolution of each curve will be longer than the time spacing between the curves The ratio of the time resolution to the receive delay step is called the overlap ratio The overlap of the TDS sweeps is used to obtain a good compromise between time resolutio
183. sponse The Time Response test is a fundamental data gatherer for many other TEF measurements Time Response information is used in setting parameters for Frequency Response measurements and in calculating intelligibility information For these reasons it is customary to make a Time Response ETC measurement the first task Time response measurements are used to eset up the frequency response test e measure the delay of a signal applied to a system under test efind the direct sound arrival in a room efind reflections find reflections that fit a pattern such as flutter echoes e observe the decay rate of sound in a room echeck the coverage in a room ecalculate the RT60 and ALcons of a room ANPLITUDE dH 70 Practice measurements Sound Lab TDS ail The Time Response test displays an Energy Time Curve that shows how energy from a system or device is released after it is excited with a sudden application of input energy confined to a given frequency band over a certain time span The results are displayed on an ETC graph with time shown on the horizontal axis and energy on the vertical axis S8 eee S je ear m iet Pda e A es moe aa RUE REO TR ST Y PU S PCT oos AS A NE TS ge ebbe JO jepara paa dh ud sn a3 20 nn ee Pe eee ee TTT TIME Hilliiecs An ETC shows the amplitude of the sound energy that arrives at any instant in the time span The Time Response quickly reveals not
184. st 4 51 4 70 Distance resolution GD 4 31 TDS 4 21 Distance Unit 4 77 4 80 6 6 Do 3D Test 4 13 Do Average 4 13 Do Frequency Test 4 11 Do Noise Test 4 11 4 43 Do RASTI Test 4 12 Do STI Test 4 12 Do Time Test 4 11 Doing Noise Test D 3 S 3 Q rt a 07 O 0 naex mil domain F 6 doppler effect F 6 Drive amp Dir 4 1 4 4 drive and directory changing 4 4 default 2 2 E early decay time 6 26 6 28 6 33 F 7 early RT60 5 24 early sound F 7 Echoes A 7 F 7 edit field 3 5 EE EEPROM 4 1 EFC F 7 ellipsoid B 12 F 7 See also space window End Receive Delay 3D 4 32 5 28 5 30 6 29 Energy Frequency Curve F 7 Enter key 3 7 Equipment arrangement ETC 6 4 STI calibration 5 15 STI RASTI tests 5 18 TDS 6 4 Erase 4 1 4 7 Error codes See Messages Escape key 3 7 ETC definition F 8 display 6 3 file format E 2 measurement 5 2 Extensions 4 6 index 3 F far field F 8 FFT B 4 F 8 File format 3D files E 25 ETC ASCII files E 2 NC ASCII files E 6 STI and RASTI E 13 TDS ASCII files E 9 File menu 4 1 About 4 9 Configuration 4 7 Drive amp Dir 4 4 Erase 4 7 Goto 4 9 Open Old 4 2 Printer settings 4 8 Quit 4 9 Save as 4 4 file size 4 3 filenames extensions 4 2 4 6 filter bandpass F 3 highpass F 11 lowpass F 13 flutter echo F 8 focused reflections F 8 Fourier transform B 4 F 9 free field F 9 Frequency Center ETC 4 16 defined A 4 Limits Start and Stop 4 17 Resolution F 9 F
185. t the measurement Add Noise to STI RASTI display 4 43 graph 5 21 5 22 table 5 21 5 22 Early RT60 5 24 equipment arrangement file format E 13 graph or table 4 58 4 29 5 25 4 59 5 19 index 10 Sound Lab TDS Index mil noiseless test 4 12 score 5 24 Signal to noise ratio 5 24 Stop Frequency 3D 4 30 ETC 4 16 TDS 4 20 Sweep Rate B 8 F 27 3D 4 30 TDS 4 20 Sweep Time F 27 GD 4 30 ETC 4 17 TDS 4 20 Sweeping through zero B 9 swept sine wave F 27 T TDS definition F 28 file format E 9 measurements 5 6 parameters 4 20 TDS Delay cursor button 6 29 Telephone numbers 1 5 Test sequencing Automatic 4 33 Averaging 4 37 DC Shift Trigger 4 34 Keyboard 4 34 Pulse trigger 4 34 Testing D 8 3 D display F 28 Time delay spectrometry F 28 delay gap F 29 domain F 29 offset F 14 Resolution 3D tests 4 31 5 29 TDS 4 21 F 20 Response ETC Parameters 4 16 Span F 29 ETC 4 17 calculating 4 18 window F 29 Time and frequericy 6 3 Time Response center frequency 6 7 display options 4 42 equipment arrangement 6 4 Heyser Spiral 4 46 Magnitude 4 44 parameters 6 1 set up loudspeaker 5 2 uses for 6 1 viewing 6 3 toggle choices 3 6 Sound Lab TDS Index Top of Scale 4 70 3D Waterfall 4 55 Frequency Response 4 49 4 50 4 5 Time Response 4 44 V Vector averaging 4 38 velocity F 29 Volts Per Reference Unit 4 77 6 6 W warning beep 4 41 waveform A 1 F 30 wav
186. test Path filename exists Overwrite Y N Appears anytime a file in the current path has the same name entered in the Save As menu If you answer Y the old data will be deleted and the new data will be saved Answer N and then change the name in the Save As menu No data current Some instructions can not be executed without data existing in memory D B P f S a m Q C 0 On screen messages mu No data available There was no data in memory to save Not enough memory for the phase cursor There was not enough free RAM found to create the phase data array Add more RAM to your computer or remove background programs such as memory managers or print queues Not enough memory for the file Disk is too full Use a different disk or delete some files Not enough memory for Nyquist Not enough memory to create Nyquist data Add more RAM to your computer or get rid of background tasks such as memory managers or print queues Not enough memory for cursor Not enough memory to create cursor data Add more RAM to your computer or get rid of background tasks such as memory managers or print queues Not enough memory for smoothing Not enough memory to create smoothed data Add more RAM to your computer or get rid of background tasks such as memory managers or print queues Not enough memory for test Not enough memory to contain the data for this test Add more RAM to your computer or get rid of background t
187. the DIP switches on the HI interface board 108 148 188 IC8 208 248 288 2C8 308 348 388 The default base address is 308 Make your choice then press Enter The following message appears Sound d b Copy demo files Choose Yor Nto continue We recommend that you choose yes Another screen will appear asking you to confirm your selections Check install selections This screen allows you to review the instal lation choices you ve made so far If you wish to make any changes at this point HI press Escape to back EA ERa up to the screen where you need to make the change Check install select ions Destination CiASLA Copy deno files If the information appears to be correct press Enter ENTER Cont inua ESC Back Up File transfer The final screen announces that the File T RET is taking place The nstall program starts transferring the files within the directories that were created on the drive you ve selected This install program will only transfer files and will not change existing CONFIG SYS or AUTOEXEC BAT files 2 5 2 6 il As soon as all files are transferred you will be given the message TDS has been installed Type SL to begin using Sound Lab TDS software Sound Lab will open in the last module of Sound Lab you used Choose the Go To option under the File menu to select TDS to open Sound Lab TDS Required files After installation u
188. the medium reverberant sound See reverberant sound field reverberation The persistence of sound in a room after the original sound has ceased It is caused by multiple sound reflections echoes that decrease in intensity with time and are so closely spaced in time as to merge into a single continuous sound which eventually is completely absorbed by the inner surfaces of the room The timing of the echoes is random and the echoes increase in number as they decay An example of reverberation is the sound you hear just after you shout in an empty gymnasium An echo is a discrete repetition of a sound while reverberation is a continuous fade out of sound Artificial reverberation is reverberation in an audio signal created mechanically or electronically rather than acoustically reverberant sound field A sound field made of reflected sounds in which the time average of the mean square sound pressure is everywhere the same and the flow of energy in all directions is equally probable This requires an enclosed space with essentially no acoustic absorption F 21 F 22 Sound Lab TDS Glossary ail reverberation time See RT A Reverberation time room modes Frequencies at which sound waves in a room resonate in the form of standing waves based on the room dimensions room time See E Reverberation time root mean square The effective dc voltage of an ac signal The square root of the mean value of the
189. the results of his explorations at a Sound Lab Foreword hill Syn Aud Con gathering in 1984 with the following preface 1 Nature proceeds without prejudice to the way you look at it 2 There are an infinite number of equally valid ways of looking at nature which he named the principal of alternatives The background of his work brought him to question Ifthere is no preferred way of observing any one event wasthere a way perhaps to travel from one alternative frame of reference to another The experimental Heyser comfortable with the validity of both the subjective and objective domains of sound evaluation began seeking maps that would enable traveling between both frames of reference He reasoned If there was a way and the event still retains the same essence what essentially doesn t change as you transfer from one alternative to another Heysers pursuit of the dynamics and mathematics underlying this assumption led eventually to its application in sound analysis which Heyser named time delay spectrometry a specific class of integral transform that maps among domains of differient dimensionality Indeed it was a small tear on the fabric of contemporary understanding of electroacoustic measuring Sound Lab Foreword ail Heyser lived to see the beginnings of the acceptance and incorporation of his thinking into sound analysis equipment and its actual application in the fields of audio medicine
190. the system has on the energy passing through it The results tell a great deal about the energy as well as the system The principal advantages of TDS measurements are superior noise and distortion rejection properties fast data gathering capability and the ability to make acoustical measurements under actual use situations In addition TDS measurements easily handle test situations in which signal delays and nonlinearity are an inherent part of the system Accuracy in TDS measurements depends on accurate measurement of both energy and time Time delay spectrometry measurements include the frequency response phase response and time response data associated with other techniques plus energy time curves and energy time frequency curves 3 D graphic display TEF cube A metaphor for envisioning how TEF displays time energy and frequency data 3 D display In TEF measurements the 3 D display shows the change in magnitude frequency response versus time for a number of individual TDS sweeps Each sweep is offset in time by a constant amount and on the screen form a three dimensional surface display The three dimensions are time energy and frequency Sound Lab TDS Glossary ai time delay gap 4A signal delay The subjective judgment by a listener of how live or dead a room is does not depend on the reverberant sound field but rather on the initial time delay gap and the ratio of direct sound level to the early reflection le
191. times more disk space and takes longer to open and display but you may use other programs such as spreadsheets to view and manipulate the data Note The format of the file may be changed at any time providing it was saved Use Open Oldto load the data into memory then change the file format and resave either under the same or a new name 4 5 4 6 Sound Lab TDS File Menu htl Save 1 This command is only available by pressing F3 Save 1 will cause Sound Lab to add 001 to the end of the current measurement file name The displayed data will be saved under that new name Forexample ROOMFILE TDSbecomes ROOMFO01 TDSor ROOMFO01 TDSbecomes ROOMFOO2 TDS when F3is pressed The data for each measurement is stored under an eight character file name Sound Lab TDS will not accept more than eight characters for the file name and it automatically adds a two or three character suffix called an extension to indicate the type of data The file name extensions are Time and distance ETC Frequency TDS STI and RASTI STI Noise NC TDS config file TCF Startup config SET Go to menu MNU 3D 3D Individual 3D HHH Sound Lab TDS File Menu hill _ Erase The command Eraseallows the removal of data Open Old B files chosen from a list box The Erase sub menu Drive amp Dir E save as shift ra follows the same path navigation routine as described gt in Open Old Before Sound Lab TDS erases
192. tion time The time it takes for sound to decay to 60 dB below the original steady state sound level is called reverberation time abbreviated T or RT60 Hoom modes If you play an amplified bass guitar through a speaker in a room and do a bass run up the scale you will hear some notes at which the room resonates reinforcing the sound These resonant frequencies most noticeable below 300 Hz are called room modes or normal modes Resonance peaks of up to 10 dB can occur They give a tubby or boomy coloration to musical instruments and should be minimized Room modes occur in physical patterns called standing waves Standing waves are uneven sound level distributions in aroom caused by sound waves continuously reinforcing themselves as they reflect between opposing surfaces Opposite walls Cor the ceiling and floor can support standing waves between them as shown in Illustration A 9 Weaker modes can occur between other surfaces A 11 A 12 LEVEL ie O sk A ARA 50 100 150 200 250 300 FREQUENCY Hz SOUND PRESSURE LEVEL Sound Lab TDS Basics of Sound mi THIRD MODE WALL WALL PEAKS ARE ROOM RESONANCES B ZN Illustration A 9 Standing wave phenomena A Pressure distribution between two opposing walls for first three room modes B Example of frequency response of a room with standing waves Sound Lab TDS Basics of Sound mil The frequencies at which the room resonates depend on the
193. to the center of the graph and then curves back up to the upper right corner The time resolution is shown by the curve marked Rt and follows an exponential path because of the logarithmic horizontal scale from the lower left side of the graph to the upper right actually lying directly below the frequency resolution curve to the right of the square root of the sweep rate This tells us that the time resolution decreases number gets bigger linearly as the bandwidth increases The frequency resolution however behaves differently As you can see in the graph if we start with a bandwidth that is less than the square root of the sweep rate the frequency resolution will increase smaller number as we increasethe bandwidth until we reach the point where the bandwidth is equal to the square root of the sweep rate As we continue to increase the bandwidth beyond the square root of the sweep rate the frequency resolution decreases The Best Frequency Resolution is equal to the square root of the sweep rate and occurs where the bandwidth is also equal to the square root of the sweep rate Why Notice that the left side of the graph is labeled TDS and the right side is labeled Conventional with the square root of the sweep rate being the dividing line This indicates that as long as the bandwidth is less than or equal to the square root of the sweep rate we are doing TDS If however we set the bandwidth to a value that is greater than the square
194. to work with a microphone requires setting the input hardware and calibrating the display The Input parameters menu includes machine settings that govern the operation of the TEF measurements Settings for the TEF input vary with the type of microphone and the type of system the TEF is analyzing Setting the input parameters gt Go to the Input menu and select Settings Set your TEF to the settings shown 2 Return to the Input menu Input Preanp Channel A LoopBack Off 24 dB Preamp Gain B 2 2 Zlustration 6 2 ota 203 Input parameters sub menu 6 5 Sound Lab TDS Practice measurements mil Calibrating the display The amplitude reading you get in a display is always accurate in a dB relative sense If you settings Calibration Reference Unit pascals need to know the absolute Uolts Per Reference Unit 0 00226 Zaro dBaHBrerence alve Dopo o amplitude of a measurement prupswetiuiu speed 1130 0 relative to O dB SPL the feet pr inches meters Illustration 6 3 Calibration sub menu 6 6 Distance Unit cent ineter feet i numbers will be incorrect unless you have first calibrated the instrument Sound Lab TDS software uses Reference Units Volts Per Reference Unit xi Zero dB Reference Value Propagation Speed and Distance Units to show data in terms of sound pressure level and distance Without this information Sound Lab TDS would show data on
195. toward bad intelligibility and 1596typically is considered the maximum allowable 825 6 26 Sound Lab TDS Practice measurements HT8O ALcons mi Early Decay Time tThe time for a reverberant sound field to decay 10 dB below the level of the direct sound Short decay times cause music and speech to sound dry or muffled Long decay times make speech unintelligible and difficult to understand It is the figure that most closely approximates how the decay time sounds to the ear RT60 Reverberation time The time in seconds for the reverberant sound field to decay 60 dB after the sound source is shut off It is calculated by measuring the rate of decay over as much decay as possible in the curve ideally the first 25 dB to 30 dB of decay and extrapolating what the RT60 would be if the decay continued at that rate An appropriate ETC RT60 and ALcons calculations begin with an appropriate ETC measurement either an individual measurement or one taken as a part of an STI data set There are three fundamental requirements to have an ETC that is valid to calculate RT60 and ALcons e The room must be large enough to have a statistical reverberant field e The ETC display on the TEF analyzer must be of sufficient duration to see the reverberant field e The sweep must be slow enough to excite the room and allow the reverberant sound to return to the TEF analyzer To be certain you sweep slowly enough you should
196. tting the hardware and software to work together In the nput menu you select the microphone preamp or line level inputs specify the reference unit values you wish to use and the computer port that communicates with the TEF e To set the input options pull down the Input menu and select Settings e To calibrate the display pull down Input and select Calibration e Communication selects communications options Input Calibration Communication reer uer mmi A rto A a A EA Y cocoa rs a ht rina aes ahr CHORD ce one EA ACIES FCRI n m Rr Illustration 4 48 Input sub menu 4 73 Sound Lab TDS Input Menu Settings sub menu Input Toggles between Line and Preamp The TEF has two inputs for each channel BNC connectors are for line level inputs and three pin XLR connectors are for microphone inputs The microphone input is connected to a microphone preamp to amplify the signal levels mum Channel Toggles between channel A and Channel LoopBack Preamp Gain A Preamp Gain B Alt Close D Illustration 4 49 Settings sub menu 4 74 Preamp B the channel on which the TEF receives data This applies to both line and a off microphone inputs 60 dB o dB The TEF analyzer can accept input from one of four signal sources Channel A Line or Preamp or Channel B Line or Preamp Loopback Toggles between Loopback On and Off Sound Lab TDS can test the TEF hardware with an internal loopback
197. ttings e Set start frequency to 100 Hz e Calculate and set a new stop frequency to maintain the same frequency span Note A start frequency below 100 Hz may be entered manually 4 17 Sound Lab TDS Parameters Menu nl Guidelines for ETC measurement parameters For the initial room measurement calculate how long it will take sound to travel the longest dimension of the room Set the time span to be at least 10 times longer than the travel time Set sweep time to be 3 to 4 times longer than the time span Sweep time effects the quality of the measurement the longer the sweep time the greater the noise immunity Select a center frequency that matches the center of the frequency range of interest Sound Lab will calculate start and stop fre quencies to maintain the selected time span Stop frequency must be greater than start frequency by 14 Hz Frequency span and number of samples change the time span Time span is calculated from the following formula 1000 x 0 85 x number of samples Time span ines 2 x stop freq start freq Use the Hamming window function for per forming acoustic measurements and the Rectangular window for performing electronic measurements O Sound Lab TDS Parameters Menu on D ETC NUN parameters S E EJ E Je 3 S Slp ls lSlSSis se PL EEL E S g gJ s C Change Resulting S S S E g8 E E S S LEJE U Update chanaes S R NC No change g gt e c
198. turned off if you change the file type Note The print command does not print overlaid curves It prints the last curve drawn on the screen Sound Lab TDS Display Menu tl Other Display options Difference Sound Laballows you to difference time and frequency measurements The Difference mode is toggled on or off When differencing measurements you first establish a reference curve The reference curve can be the currently displayed measurement a recalled file or a new measurement The reference curve will be subtracted from the next measurement performed and the differenced data will be displayed on the screen You can also recall a file from the File Open Old menu to difference against the reference When using the Difference mode each measurement can be stored on disk under the File Save as sub menu When saving the measurement a sub menu allows you to save either the a Difference Data or Cb Last file or last measurement If you choose Difference Data you will save the data as it is currently displayed If you choose Zast file or last measurement you will save the data from the last measurement or recalled file When the Difference mode is on Sound Lab will not allow parameters of the current measurement type to be changed If you attempt to make a change a message box will appear announcing Parameters may not be changed while Overlay or Difference modes are on If no data exists in memory you can t
199. u would possibly be able to see or resolve its cellular structure because you have increased the resolution dramatically Note that as you increase resolution looking at the wing you know less about the total picture i e how big it is what color the body is etc If we make a time domain measurement with a resolution of one millisecond then we will be unable to see any fine details that occur faster than one millisecond We will have a frequency resolution of 1 001 or 1000Hz The details will not disappear completely but they will be blurred or smeared in much the same way as viewing the butterfly unaided In order to measure 10 Hz we require 1 10 or 10 seconds or longer to measure one full period In order to measure one second we need a frequency of 1 Hz Or greater The same is true in the frequency domain If we make frequency domain measurement with a resolution of 1 kHz then we will be unable to see any fine details that B 5 Sound Lab TDS How TEF works TO occur less than 1 kHz apart The effect of this on a frequency response curve is to smooth it out and minimize the peaks and valleys A TES VILLE Illustration B 3 Two different resolutions of a frequency response Illustration B A is a frequency response made with 500 WY Hz resolution The same frequency response made with 1 kHz resolution is shown in Illustration B 3b Notice the smoothing effect when measuring at lower B 6 Sound Lab
200. ue Propagation Speed Distance Unit Value en en 6 19 1024 2 00E 02 1 50E 04 1 92E 00 7 71E 03 4 63E 01 3 33E 00 3 77E 00 3 00E 02 ON 4 05E 01 Pascal 2 26E 03 2 00E 05 1 13E 03 FEET Sound Lab TDS File formats Comments Always use this key word for TDS measurements Maximum of 50 characters Maximum of 50 characters Maximum of 50 characters Maximum of 50 characters Maximum of 128 characters If Critical Bandwidth is turned on then use the key word ON otherwise use the key word OFF Distance units are key words and can only be expressed in four words Note all are in upper case letters PEEL INCH METER CENTIMETER E 1 1 Parameter label eee Channel Preamp Gain A Preamp Gain B Output Level Data format Data type Data count Data 2 678063e 6 2 976732e 6 5 953464e 6 E 12 Sound Lab TDS File formats mil Comments Value 0 Line input B 1 Microphone input B 2 Line input A 3 Microphone input A 40 0 0 This is the output level used for this TDS The output level value cannot be positive and is expressed in dB below 1 0 volt rms This value is valid only when the front panel level control is in the Cal position ASCII SINGLE Data types are key words a
201. ue entered here determines the number of points at which data will be recorded on the TEF during a sweep Number of Curves 3D Sound Lab will make from 2 to 100 curves in one measurement set Pause Between Curves 3D A value entered here determines the number of seconds the TEF pauses before starting the next sweep This feature is useful when you need to change something in the physical test arrangement between sweeps For example if you are collecting polar data and need to rotate a loudspeaker between sweeps enter a value in Pause Between Curves that allows enough time to reposition the speaker and step out of the measurement sound field Test Sequencing 3D When you choose Test Sequencing a sub menu allows you to select one of four ways to start the sweep The choices are Automatic Keyboard DC Shift Trigger and Pulse Trigger Automatic When you choose Automatic Sound Lab automatically makes each sweep with the pause between them the number of seconds as set in Parameters 3D Test Pause between curves 4 33 4 34 Sound Lab TDS Parameters Menu mill Keyboard When you choose Keyboard the software waits for you to press a key before making the next sweep DC Shift Trigger This option is available to work with a remote push button accessory connected to the TEF through the external trigger connector When DC Shift Trigger is selected the software begins the measurement when signaled by a push
202. upon returning to the microphone see space window Sound Lab TDS Glossary mi ETC Time response energy time curve In TEF measurements a display of all the energy returned during the time span of interest Time is displayed on the horizontal axis energy on the vertical axis An ETC shows that at this time this much sound energy has arrived An ETC indicates how energy comes out of or is released from a system or device after it is hit with a sudden application of input energy confined to a given frequency band ETC measurements quickly reveal not only the amplitude and the time of arrival but also the density of the reverberant field its approach to exponential growth and decay and the initial time delay gap An ETC contains no frequency information other than the knowledge of the range being swept far field The distribution of sound energy at a very much greater distance from a source than the linear dimensions of the sousee and in which the sound waves can be considered to be plane waves FFT Fast Fourier Transform An algorithm for rapidly computing the Fourier Transform flutter echo A series of specific reflective returns caused by large surfaces being parallel to each other focused reflections Sound energy concentrated by a curved surface Focused reflections are usually louder than the normal reverberant field at a given time after the excitation has ceased They can be caused by domed ceilings curve
203. urement is a FULL_STI or NOISELESS STI there will be six sets of headers and ETC data Each new ETC set will begin with the ETCx key word x will be a number from one to seven as shown below ETC1 ETC2 ETC3 ETC4 ETG ETC6 SEQQ If the measurement is a FULL RASTT or NOISELESS_RASTI there will be two sets of headers and ETC data The first will be ETC3 and the second ETC5 Sound Lab TDS B Parameter label Output Level Data format Data type ASCII SINGLE Data count Data 2 643692e 5 2 891838e 5 1 943973e 5 ASCH SINGLE 511 2 095901e 5 3 915130e 5 3 417925e 5 This is a key word of the actual File formats iil Comments output level used for this ETC This value contains both the BandGainLowerFactors coded into the STI application to simulate human voice and SpeakerEQOctaveSPL values collected from the talker equalization for the appropriate band The values cannot be positive and are in dB down from 1 0 vrms Data formats are key words and can only be expressed in two key words Data types are key words and can only be expressed in key words There is currently no support for DDOUBLE This is a zero based count Data count is always equal to Number of samples 1 E 23 Sound Lab TDS File formats
204. ve delay of the first curve measured is stored and displayed as curve 001 4 31 4 32 Sound Lab TDS Parameters Menu mi The Start Receive Delay can be manually entered into the menu You can also use the cursors to enter the value directly into the parameters by using the cursor buttons that appear below an ETC display when the cursor is turned on Position the ETC cursor at the desired data point on the display and press the Skey An information box appears showing the 3D Start Delay and 3D End Delay values as determined by the cursor position End Receive delay 3D The receive delay of the last curve measured When displayed with the cursor this curve number is equalto the value at No of Curves The End Receive Delay can be manually entered into the menu You can also use the cursors to enter the value directly into the parameters When using the cursor buttons in an ETC display four buttons will appear below the display Position the ETC cursor at the desired data point and press the S key An information box appears showing the 3D Start Delayas set before and the current 3D End Delay values Receive Delay Step 3D The value entered here sets the receive delay change between the individual curves Bandwidth 3D The value entered here determines the size of the sweeping filter i e what the filter can see See Appendix A How tbe TEF works Sound Lab TDS Parameters Menu Number of samples 3D The val
205. vel See initial time delay time domain In TEF measurements that portion of the TEF cube in which time is the independent variable Time domain measurements are made with time running horizontally along the axis time resolution See resolution time time span The time during which we listen for the effects of the signal on the device under test and vice versa It is shown in TEF ETC measurements as the amount of time on the X axis on the screen It is dependent on the frequency span of the sweep and the number of data points displayed time window A range of time over which signals are accepted by the analyzer The relation between time window bandwidth and sweep rate is T B S where T width of time window in seconds B bandwidth in Hz and S sweep rate in Hz sec see space window two port measurement Measurement of a system by comparing its output signal to its input signal velocity distance traveled multiplied by the time elapsed F 29 F 30 Sound Lab TDS Glossary l wavelength A wavelength is the distance traveled by a wave in a time of one cycle The distance measured along the direction of propagation between two points which are in phase on adjacent waves Low frequencies have long wavelengths high frequencies have short wavelengths waveform A graph of a signal s sound pressure or voltage vs time The waveform of a pure tone is a sine wave weighted Referri
206. vels at 1130 feet second during a two millisecond time window it will travel 2 26 feet Therefore we have a 2 26 feet distance window This means that any signal that has a total path length that is within plus or minus 1 13 feet 1 2 of 2 26 feet of the direct sound will be included in our measurement Space window considerations On the TDS analyzer the space window is determined by the settings of the bandwidth and sweep rate For example a 10 foot space window would correspond to a bandwidth setting of 88 5 Hz at a sweep rate of 10 000 Hz second Here is the appropriate formula D BC S where B bandwidth setting of tracking filter in Hz S sweep rate in Hz second D space window in feet C speed of sound 1130 feet second The larger the space window the lower the frequency that can be measured accurately That is the lowest frequency that can be measured without interference decreases as the space window increases Therefore a s 3 Q r Y C 0 How TEF works TI Reflecting TDS ellipsoid Illustration B 4 Tbe space window or TDS ellipsoid relatively large empty room is needed for low frequency measurements This applies to all measurement systems As stated before reflections from surfaces at the edge of the space window ellipsoid are attenuated 3 dB This attenuation may be inadequate to achieve sufficient measurement accuracy Reflections 3 dB below the direct sound level ca
207. vels measured between 7 00 pm and 10 00 pm and 10 dB is added to all levels measured between 10 00 pm and 7 00 am to account for the need for more quiet during sleep hours Leq noise measurement Equivalent continuous sound level The steady level which would produce the same sound energy over a stated period of time as the specified time varying sound Useful for studying long term trends in environmental noise A single number is used to define an entire measurement session Sound Lab TDS Glossary mi Ln noise measurement The level exceeded N of the time e g L90 the level exceeded 90 of the time is commonly used to estimate ambient noise level level The degree of intensity in dB of an audio signal liveness A subjective description of a room related primarily to the average reverberation time of the middle octaves centered at 500 and 1000 Hz and to the balance between the direct and reverberant sound levels It is also related to the volume of the room relative to the audience area lowpass filter A filter that passes frequencies below a certain frequency and attenuates frequencies above that same frequency A high cut filter mean free path The average distance traveled by sound between successive reflections near field That part of a sound field usually within about two wavelengths from a sound source where there is no simple relationship between sound level and distance NC curve s Nois
208. we need to make is which frequencies we re interested in examining and we will set the Start and Stop Frequencies accordingly Because of the small size of the room we cannot set the Start Frequencytoo low because of the correlation between wavelengths and the size of the space Recall that from the Time Response ETC display we saw that there was 1 2 feet of space before the first reflection appeared so we need to set the Distance Resolution small enough to keep the reflection out of the measurement Set by sweep time and frequency span Entered via F4 Illustration 6 11 Setting parameters forthe Frequency Response test 6 16 Bandwidth is automatically entered when you set the change as the distance distance resolution resolution is changed Sound Lab TOS Practice measurements Till Enter the following settings in the Parameters Frequency Response menu Time Hesponse LETC Frequency Response CDs Changes Delete Current Data Start Frequency Frequency span Stop Frequency Sweep Time Hi Sweep Rate Resolution Frequency 4 3j T ine A Best Frequency Resolution Receive Delay gt Bandwidth Number of Samples ALt C ep ia Po ee ce TEE INIRE a ea a em eee ea Seen Salk EE Dem baat E uci tact ere ne E eae Frequency and time resolution We want to measure within a space that will exclude the first reflection that occurred 1 2 feet from the dir
209. wn Arrow key to highlight Alt Undo then press Enter e Hold down the Alt key and press U Illustration 5 5 Alt Close action button Illustration 3 6 Entry cursor Illustration 3 7 Escape key Sound Lab TDS Navigation mill Helpful features for working with the software Action buttons Usually appear at the bottom of a menu or sub menu and cause an immediate action to occur when chosen Some of the action buttons common throughout the menus are Alt Close Accepts the parameters as presented and closes the window Alt Undo Returns all settings to the original settings in the window Function keys The Function keys F1 F10 allow you to enter many commands without selecting a menu Function keys may be used in conjunction with the Control Shift or Alternate keys Enter key Press the Enter key at the end of numeric entries such as entering sweep rate or start and stop frequencies When you press Enter the program accepts your entry and you can continue with another command on the menu Escape key In numeric or typed entries press the Escape key Esc to cancel a data entry and return to your previously entered data The Escape key is also used to cancel a test in progress Note that the Escape key does not return you tothe previous menu The Aft Close key combination returns you to the previous menu or to the menu bar 3 7 Sound Lab TDS Navigation TIT Message boxes Perti
210. you really want to quit Choose Yes or No Illustration 4 10 Go to sub menu File Do Tine Test _ XETC _ FR Frequency Test TDS s Noise Test STI Test RASTI Test 3D Test Do Average Illustration 4 11 TDS Measure menu NC Sound Lab TDS Measure Menu ill Measure menu Starting the test sequence The commands in the Measure menu start the Sound Lab TDStest sequence Sound Lab will perform the measurement with the settings made under the Input and Parameters menus It will then display the results on the screen with the settings made under the Display menu The sub menus under the Measure menu are F6 F7 F8 Shift F8 F9 Shift F9 Do Time Test sends a sweep of selected frequencies into a system or device and calculates and displays the amplitude of energy received over a specified time period The Time Response test is useful to pinpoint the arrival times of energy at a microphone RT 69 ALcons and Early to Direct Farly Reverberation information is derived from the Time Response Do Frequency Test sends a sweep of selected frequencies into a system or device and calculates and displays an amplitude versus frequency plot The frequency response is used to find the true response of a loudspeaker system or device in the frequency domain Do Noise Test gathers noise data over a specified period of time in eight octave bands and displays the results on a noise criteria NC graph showing octave
211. ystems B 7 B 8 CD S a r Q O J 0 How TEF works uil By deriving one domain from the other we do not learn anything new about the thing we are measuring We have merely converted our description of it from one domain to the other The description in either of the domains is sufficient to describe the other The factors that should determine which domain to measure are those of convenience If for example one domain permits measurements in seconds rather than minutes then the domain providing the faster measurement should be used Because the TEF Analyzer measures in the frequency domain it is able to achieve significant increases in signal to noise ratio over equivalent time domain techniques The accuracy and acuity of the measurement depends entirely on the sensitivity of the measuring instrument and the resolution of its display In general when measuring a system make initial measurements in wide bands of frequency or wide slices of time then narrow these bands to increase the resolution of the measurements interrelated parameters Sweep rate Slow sweeps can be used to provide high resolution TDS measurements in noisy environments or environments where the sweep level must be below the perceptible level of the noise A zero sweep rate is mathematically equivalent to a single fixed frequency At slow rates any amount of frequency resolution is available at the expense of time information

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