User Manual
Contents
1. t of tf F F FF F 4 Save Background Start Measurement FR View View Distortion file color measurement setup compensation magnitude magn phase plot Figure 2 2 Toolbar icons Ready L 2 7dB R 3 3dB Stepped Sine Response Figure 2 3 Status bar shows peak level ref full scale of left and right line inputs Start Hz 80 StopiHz 20000 Step 1 120ct Delay ms 0 00 AutoOvr 7 Start Hz combo box chooses start frequency Stop Hz combo box chooses stop frequency AutoOvr check box if checked on new measurement automatically sets current curve as overlay Delay ms edit box enter delay for phase estimation Changes graph top magnitude margin Fit plotted curve to graph top magnitude margin Changes graph magnitude range Opens dialog box for the setup of graph margins Changes graph high frequency margin Changes graph low frequency margin aja le wef b ues Figure 2 4 Top and right dialog bars Images of graphs and windows can be copied to Windows clipboard or saved to the file in a three image formats png bmp and jpg It is recommended to use png format Obtaining copy of the full window picture is simple User needs to simultaneously press keys Ctrl P After that command the window picture will be saved in the System Clipboard from were the user can paste it in other opened Windows applications MS Word MS Paint Keys Ctrl Alt P activate command to save that image in the file T2. Amm Al TEPS User Manual l kml UJ WIL al V E a i i Cil 3 2 Linearity Testing For the linearity measurements we use the user interface defined in the window Linearity Function shown in Fig 3 4 This window is opened by the menu command Record gt Linearity function Ee Linea rity Function untitled wsl E iol x File Edit Measurement channels Y channel Left Z X channel Right sampling rate Hz 48000 h Excitation sine voltage range Frequency Hz 1000 Start value V rms 0 1 max lt 0 632V Use logarithmic steps s Response OV rms Linearity test 10 0 0 5 Number of steps 10 0 001 Power reduction 3 duty cycle 0 0001 0 0001 0 001 0 01 0 1 1 0 10 0 Excitation V rms Figure 3 4 Linearity Function window Linearity testing is a dual channel measurement We measure some system excitation as X signal and the system response as Y signal The excitation signal is generated by STEPS sine signal generator The measurement setup is defined in three sections Measurement channels section Y channel chooses soundcard line input channel for measuring system response X channel chooses soundcard line input channel for measuring system excitation Sampling rate chooses sampling rate in Hz Excitation sine voltage range section Frequency Hz enters sine frequency Start value V rms enters start minima
3. Input Figure 1 3 Voltage probe with soundcard input channel overload protection 1 3 Heterodyned Measurement of Sine Response The idea of a heterodyned measurement of a sinusoidal response is as follows We assume that a time invariant system is excited with a sinusoidal signal g t of known frequency amplitude and phase At the output of the system we measure a noisy and distorted signal y t N y t A sin 0t 9 gt A sin kot p n 0 k 2 Aj is a amplitude of the base sinusoid or base harmonic 01 is a phase of the base sinusoid n f is a noise and Ax is a amplitude of k th harmonic distortion We want to estimate the amplitude and the phase of harmonic components with a minimal noise influence We can achieve that by using a heterodyned technique we extract k th harmonic component from y t by multiplying it with a complex form of the input signal that has known frequency g t sin kat jcos kat je i 12 and integrating the product y t gx t in a time T What we get is k th signal harmonic filtered with a heterodyne filter of bandwidth equal to 1 7 The former procedure is equivalent to the estimation of the k th harmonic component by the Fourier series expansion T T 1 A A 1 e jka C jz hoa gt 00504 j sn D j other _harmonies noise e dt 0 0 Note the multiplication with j is arbitrary that way we get the proper phase estimation An exact solution is possible only
4. 2 2 3 ASIO Driver Setup ASIO drivers are decoupled from the operating system control They have their own control panel to adjust native resolution and memory buffer size The buffer is used for transfering sampled data from the driver to the user program User opens the ASIO control panel by clicking button Control Panel in the Audio Device Setup dialog Fig 2 12 shows an example of ASIO control panel Preferences Buffer Size 20 ms Bit Depth 32 bit a OF Lancel I Per Application Preferences Figure 2 12 E MU Tracker Pre ASIO Control panel for setting bit resolution and buffer size In music applications user usually sets buffer size as small as possible with stable operation That gives the lowest input output latency system introduced delay In STEPS latency is not a problem as it is encountered in software but it is not recommended to use buffer with size larger than 2048 samples or smaller than 256 samples Some ASIO control panels express the buffer size in samples while other express the buffer size in time ms In that case we can calculate the size in samples using the following expression buffer_size samples buffer_size ms samplerate kHz number_of_channels Some ASIO drivers allow setup of buffer size in samples that 1s a power of number 2 256 512 1024 In that case STEPS adjust buffer size automatically STEPS always works with two input channels an
5. total harmonic distortion in calculated from first twelve harmonics D2 the second harmonic distortion D3 the third harmonic distortion D4 the fourth harmonic distortion D5 the fifth harmonic distortion D6 the distortion due to 6th to 12th harmonics D6 100 sqrt Ac A77 A127 A1 depending on selected check box in the section D range In the same section there are following controls Top sets top graph margin Bottom sets bottom graph margins Autofit sets graph vertical margins to fit into the distortion range Mouse or keyboard cursor keys move graph cursor The values of distortions at current cursor position are shown below the graph On the right graph side there is a legend for curve colors Controls at the bottom of the dialog box are Range list boxes sets low and high frequency graph margin Autofit button sets graph horizontal margins to fit in measured frequency range Copy button copies graph to clipboard 34 STEPS User Manual Thick pen button check box to set plotting pen width to thick or thin B W button check box to change the background color to White or Black If there is one or more overlay plots in the frequency response window then the distortion window shows automatically overlay check boxes see Fig 2 27 which allows to control the view of distortions for the first overlay The right plot legend shows colors of overlay distortions
6. 2000 Transient time ms enters the transient time 0 to 2000ms I O delay ms enters the estimated constant delay in the measured system Intra burst pause ms enters the duration of pause between generation of two sinusoids Set current response as overlay on new measurement automatically sets current curve as overlay In section Stepped Sine Generator Start frequency Hz enters the starting frequency in Hz Stop frequency Hz enters the ending frequency in Hz Frequency increment chooses an increment 1 6 1 12 1 24 or 1 48 octave Generator level dB re FS enters the output generator level Test frequency Hz enters frequency in Hz for testing I O levels Mute generator switch off transient suppress sine switch off transients but measurement time is enlarged 22 Button Generate starts generation of test sine signal and peak meters show input levels Button Default sets the default measurement configuration Button OK accepts measurement configuration Button Cancel rejects changes in measurement configuration 2 5 Measurement Procedure If you have done the audio device setup the generator setup and the measurement setup you are ready for measurements 1 Connect voltage probes or other sensors to measured system output In dual channel mode connect voltage probes to measured system input 2 Click the menu item Record gt Start or click the toolbar icon gt l 3 Measurement will be re
7. P key copies a whole window bitmap to the clipboard Ctrl Alt P key saves a whole window bitmap to the file Ctrl B key changes background color Ctrl A key sets currently plotted curve as overlay Ctrl M key opens overlay manager window 12 i Km GC F LE LIQ ear AA ran DE p gt rz VECI IU c E io f ew Www VECER E LICI 2 2 Audio Devices Setup Before you start measuring you have to setup your hardware and audio devices by clicking the menu Setup gt AudioDevices or by clicking the toolbar icon You will get the dialog box for the audio devices setup shown in the Fig 2 6 Audio Devices Setup Soundcard driver WDM Windows multimedia driver Control Panel Microphone SoundMAX Integrated Wave Format Speakers SoundMAX IntegratedD Float z I O Amplifier Interface Lineln Sensitivity 2000 LineOut Sensitivity mvpeak left ch mVpeak left ch Ext left preamp gain 1 L R channel diff dB Power amplifier gain Microphone J Microphone Used On Left ch Sensitivity mv Pa 5 Figure 2 6 Dialog box for audio devices setup The Audio Device Setup dialog box has following controls In section Sound Card Soundcard driver chooses the type of soundcard driver WDM windows multimedia driver or one of installed ASIO drivers Input channels chooses the soundcard input stereo channels ASIO driver can have large number of channels Output Device chooses
8. W changes background color to black or white Copy copies graph to clipboard Click on button Setup or right mouse click in the graph area opens the dialog box Distortion displacement graph setup It is shown in Fig 3 9 Distortion displacement graph setup x Y axis range Distortion Log Y axis 86 Displacement mm Log X axis T Show 2nd and 3rd harmonic distortions Update Default cancel OK Fig 3 9 Dialog box for Distortion displacement graph setup Dialog box Distortion displacement graph setup has following controls Axis Type section Log Y axis sets logarithmic or linear Y axis Log X axis sets logarithmic or linear X axis Num decades chooses number of decades in logarithmic Y axis Y axis range section Distortion enters Y axis range for distortion graph Displacement mm enters Y axis range for displacement graph X axis range section High V enters voltage for the graph right margin Low V enters voltage for the graph left margin If check box Show 2 and 3 harmonic distortions is checked the graph shows additional distortion curves The window has two menu items File and Edit File commands are Open retrieves data from binary vdx file Save saves data in binary vdx file Export saves data in textual files in plain ASCII or Excel CSV format Info shows information about current file Edit
9. applying the inverse of sensor FR to measured FR The menu command Setup gt FR compensation or click on icon ike gets the dialog box Frequency Response for Compensation shown in Fig 2 14 The dialog has a few controls and a graph that shows the frequency response which will be used for FR compensation The button Load opens the dialog for loading ASCH files that contain frequency response data The file name must have extension MIC and data entered in lines of text Lines that start with a digit or dot characters must contain at least two values first value is frequency in Hz and the second value is 20 STEPS User Manual magnitude of frequency response in dB The third value is optional It may be the value of phase or any other text that will be treated as comment All other lines are treated as comment After successfully reading of the compensation file the path of the file will be shown in the box below the graph Fa T Frequency response compensation kaa Magnitude dB ee ee ee eee U J U U J U U 4 I U 1 U ane de ee Le Le Show interpolated 10 100 1000 10000 values Cursor 46 3 Hz 0 3 dB Frequency Hz k C Src audio 1 Arta 103 MB550 B mic Load Use frequency response compensation Figure 2 14 Typical frequency response of an electret microphone For example file MB550 B shown in Fig 2 14 has content microphone mb550 freq Hz Magn dB 48 280 0 34 48 9
10. as in Fig 2 10 Then mute Line In and Mic channels if exist 4 Click on the tab Advanced to set the channel resolution and a sample rate as in Fig 2 11 5 Repeat previous procedure 1 to 4 for recoding channel and choose the same sampling rate as in the playback channel x Playback Recording Sounds Communications Select a playback device below to modify its settings g Speakers 3046 Audio Device Digital Output Speakers SoundMAX Integrated Digital HD Audio Default Device SPDIF Interface Figure 2 9 Vista Sound Control panel 16 STEPS User Manual E Speakers Properties General Custom Levels System Effects Advanced Speakers u B w Balance Line In p 0 do aac Microphone yJ fag Batane m B w Balance CD Player B w Balance l Figure 2 10 Playback channel properties Output levels E Speakers Properties 2 General Custom Levels System Effects Advanced Default Format Select the sample rate and bit depth to be used when running in shared mode 8000 Hz DVD Quality Be Test Exclusive Mode IY Allow applications to take exclusive control of this device IF Give exclusive mode applications priority Restore Defaults Figure 2 11 Setting the native bit resolution and sampling rate in Vista 17 Note Many drivers do not work stable under Windows 7 In that case please use ASIO driver if soundcard has one
11. aw Copy setup Fig 3 8 Distortions and Displacement measurement window Window Distortion and displacement has following controls Measurement channels section Response channel chooses the microphone input channel Sampling rate Hz chooses the current sampling frequency Use displacement sensor on other channel check 1f sensor for the displacement measurement 1s connected to the other input channel Sensitivity mV mm enters sensitivity of displacement sensor Excitation sine voltage range section Start value V rms enters stepped voltage amplitude start value Stop value V rms enters stepped voltage amplitude stop value The maximum value is denoted below this control a power amplifier output voltage is reported Number of steps enters number of repeated measurement with voltage increment Logarithmic step increment switches voltage steps to logarithmic increment THD break value enters limiting value for distortion after which measurement stops Sine frequencies section 46 Frequency f1 Hz enters fundamental frequency for harmonic distortions measurement Use f2 8 5f1 U1 4U2 check box to use intermodulation distortions measurement Integration constants section Integration time ms enters RMS detector integration time Transient time ms enters transient time as time necessary to reach the steady state condition Bottom Buttons Record starts or stops measurements B
12. box for calibration of soundcard and microphone Three sections lead to the calibration of a soundcard output left channel b soundcard input left and right channels and c microphone calibration Note during calibration sampling rate can be set to 44100 or 48000 Hz 2 3 1 Calibration of Soundcard Output Left Channel It is recommended to follow this procedure Connect the electronic voltmeter to the left line output channel Press the button Generate sine 400Hz It changes label to Stop Generator Enter the voltmeter readout in edit box Press the button Stop Generator Press the button Estimate Peak Output mV The estimated value will be shown in the box Estimated mg ee 19 7 If you are satisfied with the measurement press the button Accept and the estimated value will become the current value of the LineOut Sensitivity Also it will be automatically entered as a value for the input channel calibration 2 3 2 Calibration of Soundcard Input Channels You can use an external generator or the output channel of the soundcard to calibrate the input channels In case of using the output channel of the soundcard as a calibrated generator 1 Set the left and the right line input volume to maximum Connect the left output to the left line input 3 Press the button Generate sine 400Hz and monitor the input level at bottom peak meters If the soundcard input is clipping lower the level of input volu
13. output mixer in Windows XP Note Most professional audio soundcards have their own program for adjustment of input and output channel or have hardware control of input monitoring and input and output volume controls 15 2 2 2 WDM Audio Driver Setup for Windows Vista 7 8 Microsoft has changed their approach in control of sound devices in Vista Win7 Win8 Now operating system also sometimes in conjunction with control programs of professional soundcards is responsible for setting soundcard native sampling rate and bit resolution Operating system changes native resolution to floating point format for high quality mixing and eventually for the sample rate conversion For ARTA this means that it is strongly recommended to use resolution type Float and sets the sampling rate to the native format Access to these values is in Windows sound control panel which user gets by clicking the button Control Panel in the Audio Device Setup dialog Fig 2 9 shows Vista Win 7 control panel that has four property pages As first step user has to adjust Playback page and later repeat the same procedure for Recording page Adjustment steps are 1 Click on channel info to choose a playback channel It is not recommended to use the measurement channel as a default audio channel 2 Click on button Properties to opens channel Sound properties dialog 3 Click on the tab Levels to open the output mixer
14. the soundcard output stereo channels Generally user chooses input and output channels of the same soundcard mandatory in ASIO driver mode Control panel button if WDM driver is chosen it opens sound mixer on Windows 2000 XP or Sound control panel in Vista Win7 If ASIO driver is chosen it opens ASIO control panel Wave format on Windows 2000 XP chooses Windows wave format 16 bit 24 bit 32 bit or Float Float means IEEE floating point single precision 32 bit format It is recommended to use 24 bit or 32 bit modes when using a high quality soundcard many soundcards are declared as 24 bit but their real bit resolution is less than 16 bits On Windows Vista Windows 7 it is recommended to choose resolution type Float This control has no effect in the ASIO mode where a bit resolution has to be setup in the ASIO control panel 13 In section I O amplifier interface LinelIn sensitivity enters the sensitivity of the line input 1 e peak voltage in mV that corresponds to the full excitation of the line input LineOut sensitivity enters the sensitivity of the left line output i e peak voltage in mV that corresponds to the full excitation of the line output Ext preamp gain If you connect a preamplifier or voltage probe to the line inputs you should enter the gain of the preamplifier or probe attenuation in the edit box otherwise set it to unity gain LR channel diff enters the difference between the level of
15. will have tick marks e Ifthe check box Add subgrid on magnitude axis is checked FR and Spectrum graphs will have denser magnitude grid This option disables the dotted grid option 29 STEPS User Manual Color Setup x gt 7 i rar Sa Sai i Add axis tick marks 7 Add subgrid on magnitude axis Figure 2 21 a Dialog boxes for graph color setup in black background mode Color Setup l X Basic colors Graph background a a Plot peni n Plot pen Ft Plot pen3 Plot pen4 Ss Overlay NEH Overlays E Overlay Overlay10 H Overlay11 RH Overayi2 E Overlay13 ios Ovelayi4 ATI Overlay15 R All overlays use same color Figure 2 21 b Dialog boxes for graph color setup in white background mode 30 STEPS User Manual 2 x Color Basic colors ll 8888 ll lB REHEAT ll IBEEHN 1 Define Custom Colors gt gt Carel Figure 2 22 Standard Windows dialog box for choosing colors 2 8 3 Editing Plotted Curve For editing plotted curve we use following commands Smooth Magnitude smoothes magnitude in octave bands 1 1 octave 1 2 octave 1 3 octave Scale level scales the magnitude level LF box diffraction scales frequency response with transfer function of LF loudspeaker box diffraction Cut below cursor cuts plotted curve below the cursor position Cut above cursor cuts plotted curve above the cursor po
16. 2 3 4 3 6 7 In Audio device setup dialog click the button Control panel to open the Windows Master Volume dialog box which is shown on Fig 2 8 Click on menu Options gt Property and select soundcard channel that will be used for output playback as shown in Fig 2 7 Mute Line In and Mic channels in dialog Master Volume Fig 2 8 Set Master Volume and Wave Out volume to maximum Click on menu Option gt Property and select soundcard channel that will be used for input and enable Line In and Mic channels in recording mixer Choose Line In or Mic Input Normally STEPS uses Line In input on which external microphone amplifier should be connected Set volume control of Line In to some lower position Later it will be set more precisely 14 STEPS User Manual Properties Mixer device Realtek HD Audio output gt Adjust volume for f Playback Recording f ther Show the following volume controls Waster Volume Wave SW Synth CD Player Mic Volume PC Beep Figure 2 7 Dialog for choosing soundcard and input output channels Options Help Master Volume Wave CD Audio Line In Microphone Balance Balance Balance Balance Balance Volume Volume Volume Volume Volume ot Ee als T gk ph I Mute all Mute T Mute Iv Mute Iv Mute Advanced Advanced Intel r Integrated Audio Figure 2 8 Typical setup of a soundcard
17. 2k 5k 10k 20k f 358 9 Hz Magn 75 50 dB HZ D2 49 59 D3 50 99 dB Figure 2 17 Typical frequency response and distortion level of a small multimedia loudspeaker Ca Oma oo gOS m D2 m Magn You can define the current plot as overlay plot or you can load an overlay plot The number of overlay plots is not limited File formats and manipulations are explained in the next section 2 6 Overlays The overlay is a curve that is permanently shown besides the currently shown measured curve The user can set the current frequency response curve as overlay he can also define some overlays to have the crossover target filter response Manipulations with overlays are handled with menu Overlay It has following pop up items Set as overlay saves the current curve as an overlay Manage Overlays opens dialog box FR Overlay Manager Delete all deletes all overlays Delete last deletes last overlays Load loads overlay from STEPS hsw file Load imedance overlay loads an impedance overlay from zma or lim file Delete imedance overlay deletes impedance overlays Advanced manipulations with overlays can be done using the dialog box FR Overlay Manager shown in Figure 2 18 It is activated by menu command Overlay gt Manage Overlays 24 STEPS User Manual Overlay colors x avll x hsw avl2 x hsw J avl3 x hsw avl2 x edited hsw Figure 2 18 Dialog box FR Overlay Manager and dialog box
18. 36 U Ze 49 601 OZA DUG SL The check box Show interpolated values enables us to see the interpolated FR curve that will be used in FR compensation The button Copy copies current graph picture on Windows clipboard The combo list box Range dB sets graph magnitude dynamic range 10 100dB The button Use frequency response compensation enables disables frequency response compensation q y resp p q y resp p 21 2 4 Measurement Setup For the setup of measurements use the Measurement setup dialog box shown in Fig 2 15 You get it by clicking the menu Setup gt Measurement or by clicking the toolbar icon X Stepped Sine Generator Start frequency Hz 20 00 7 Stop frequency Hz 20000 00 i Frequency increment Sampling frequency Hz 48000 Min integration time ms 200 Transient time ms Generator level dB re FS Test frequency Hz 1000 Mute generator switch off transients Iw I O delay ms Figure 2 15 Measurement setup The Measurement setup dialog box has following controls In section Measurement System The first combo box chooses mode of measurements Dual channel frequency response measurements Single channel level measurements Response channel chooses the Left or the Right channel Sampling frequency Hz chooses the sampling frequency from 11025 to 192000 Hz Min integration time ms enters the minimal integration time 0 to
19. During the measurement various types of distortion will be measured and presented graphically harmonic distortion THD D2 D3 and intermodulation distortions MD2 MD3 3 3 1 Definition of Xmax AES recommendation 2 1984 defines the Xmax as the voice coil peak displacement at which the linearity of the motor deviates by 10 Linearity may be measured by percent distortion of the input current or by percent deviation of displacement versus input current Manufacturer shall state method used The measurement shall be made in free air at fs This definition 1s not quite clear and effort has been made to introduce a new standard for definition and measurement of Xmax This new draft standard 1s available now as IEC PAS 62458 Sound System Equipment Electroacoustical transducers Measurement of large signal parameters This standard is based on the W Klippel s definition for Xmax The voice coil peak displacement Xmax at which either the total harmonic distortion THD or the nth order modulation distortion where n 2 or 3 exceeds 10 in the sound pressure radiated by the driver in free air excited by the linear superposition of a first tone at the resonance frequency fi fs and a second tone f2 8 5 fs with an amplitude ratio of 4 1 The total harmonic distortion assesses the harmonics of f and the modulation distortions are measured by the modulation components f2 n 1 fi according to IEC 60268 3 3 2 Measurement of Xmax Fol
20. Overlay colors In the dialog some buttons replicate menu commands Add overlay sets current curve as an overlay Delete all deletes all overlays Other buttons enable advanced operations on selected list box items Replace sel replaces selected overlay with current curve Delete sel deletes selected overlays Color changes color of selected items using the dialog box Overlay Colors shown in Figure 2 18 Mouse click on List box item has following effects Single click selects list items Single click on check box makes overlay visible or invisible Double click enables editing of overlay names All list items can be set visible by pressing button Check All 2 7 File Manipulations The STEPS uses special binary format to keep measured data in files whose names end with extension HSW Besides measured data HSW files can contain user defined text of arbitrary length User can enter the text in the edit box of File Info dialog see Fig 2 19 This dialog can be opened by clicking menu command File gt Info 25 STEPS User Manual File Info x requency increment 1 12 octave um frequency points 58 um channels 2 Jicrophone measures system output icrophone sensitivity 10 00 mV Pa User additional information Figure 2 19 Dialog for viewing and entering file information The format of binary HSW file is as follows i char filesignature 4 iour Signature characters ms N y DI un
21. STEPS Program for Frequency Response Measurements Using Heterodyned Stepped Sine Technique User Manual Version 1 8 5 Ivo Mateljan Artalabs J Rodina 4 21215 Ka tel Luk i Croatia February 2015 Copyright Ivo Mateljan 2004 2015 All rights reserved Content TAIN TFRODUC TION a a dada o e o Ara a ed kaja ee eee da Kia 3 IV REOUIREMENIS 2 ae a i kojo gi oo AE sl ao a E a E va 3 1 2 MEASUREMENT HARDWARE SETUP eena vana a aaa vana aaa vana aaa aaa aaa aaa aaa aaa aaa aaa nana 3 1 3 HETERODYNED MEASUREMENT OF SINE RESPONSE aaa aaa aan ovaa av nauna anna aaa aaa a aaa aaa aaa aaa aaa aaa aaa 5 2 USING STEPS FOR STEPPED SINE TESTING ccssccsscccssccscccscccccsccscccscccsecccscccscccscccscccsscccesceeeee 8 ZA DEIR Se MENUS snaga bi bina s aa odana td o na s asia ad a otada radona ED 11 2 AUDIO DOE VICES OE UP tex casnntoenanerbastascudsouautareadatonas nies saccade ninenaruniaemndetbasuarunt at ota dana si aa donosi hda i dna a 13 2 2 1 WDM Audio Driver Setup for Windows 2000 XP 00 aaa kakaa aaa 14 2 2 2 WDM Audio Driver Setup for Windows Vista 7 8 16 E OZA BTEKO IVOR SOLID osi tita dao ove 18 2 3 SOUND CARD AND MICROPHONE CALIBRATION 0200 aaa va aaa ana a ana ana vanno anna aaa aaa aaa aaa Ea 19 2 3 1 Calibration of Soundcard Output Left Channel aaa 19 2 3 2 Calibration of Soundcard Input Channels evidentan kde 20 233 Cali bral OMO TRE MIEFODRORNE ito add i o n
22. THDo D20 D30 D40 D50 D60 ES Distortion 0 Autofit M THD T D4 Dz os If D3 D IF THD T D4 Mo p05 20 50 400 200 500 tk 2 5k 40k 20k D3 J D F50 2Hz THD 0 00069 D2 0 00063 D2 0 00028 f Hz mel zlefo ze pam posjeo m Figure 2 27 The Distortion window with a current an overlay distortions plotted 35 2 10 Time Record The time record of the last recorded signal can be seen in a Time record window shown on Fig 2 28 It can be activated by clicking the menu View gt Time record or by clicking the toolbar icon R Time record O x File Edit Time record W Zoom 1 64 let Offset 0 768 0 394 Gain Max 0 000 Min 0 394 Zoom 0 788 gt mn 704 6336 11965 17600 23232 samples 7 Cursor 612 016 mv 47 657 ms 9152 Gate 29 000 ms 5566 Figure 2 28 Time record of the last captured signal The plot shows a properly scaled time record of the input signal The yellow line denotes the cursor position and the red line denotes the marker position User sets the cursor position by pressing and dragging the left mouse key and marker position by pressing and dragging the right mouse key Double clicking the right mouse button turns the marker on and off The Cursor label denotes the report for the magnitude of the signal at the cursor position time in ms or sample position in braces The Gate label denotes the report
23. a nai i t dii said dij i i 20 2 3 4 Frequency Response Compensa Onser eserse danda danas di i ista EERS EEE ENEN va 20 GGMEASUREMENI SETUP podao E i ja Ai EA E ji eee 22 EDNIEASUREMENT PROCEDUR Borean on Gada nokije iti je dva 23 AD ONTT EAT i o oj ro in Ga nono ib ita e dk 24 Doge MTs NVANIPUPA TION or eaten ga eh i s da BL Gi E A 23 2 OGGRAPH SETUPAND EDITING sa 063 a ae a ti zed a tr zada rek 28 DiMA Ney TO so dia i od ji a i e ad i on az ao 28 262 Bome trophic ors and NES E ek ost NE oi se das ot 29 LS POI SLOW CO CHI Vez pices cee E SR De sd DE i osi e abs st 3 2 8 4 Low Frequency Loudspeaker Box Diffraction SCaling aaaaaaaaa aaa 32 249 PERCENTAGE DISTORTION PLOT ips cis on na a BG oa oa eb awe ba PARP A ve a EEA a 33 2 KO TIME RECORD goes vss ipsa s o a Bl RS RUGS SS Sh ARGO O RD ae RE A Rp 36 3 USING STEPS FOR STEPPED AMPLITUDE TESTING ccssccssccccccccsccsccccccccscccscccsccccsscccceees 38 Sill DISTORTION VS AMPIATUDE TESTING rasa inire A iaaa EAE OaE AOE aE A SOTOAN 38 3 2 VINEARIT S TESINE EA E aE O A AO 42 3 3 DISPLACEMENT AND DISTORTIONS TESTING 0ccccccccseccscccsecceccescceseceeuceuseseseceeecseseseseseeceusesuseceseseusess 44 BaD UOO A MO ase ojos e a OOO OEE 44 SO ME uUremEenT ONA TUN ana aid dj e o o 44 3 3 3 STEPS User interface for measurement of A maX ie ada o 46 3 4 LOUDSPEAKER DISTORTION LIMITED MAXIMUM SPL 0aa0aa aaa av nana ovaa a ana aaa naa va vana aaa aaa aaa aaa va
24. board 39 The right mouse click in the graph area or click on button Setup opens the dialog box Distortion graph setup It is shown in Fig 3 2 Y axis range Distortion 20 Figure 3 2 Dialog box Distortion graph setup Dialog box Distortion graph setup has following controls Axis Type section Log Y axis sets logarithmic or linear Y axis Log X axis sets logarithmic or linear X axis X axis measured check box to set x axis labeling to measured or estimated RMS value the measured value is RMS value measured at soundcard input and the estimated value is RMS playback value on line output multiplied with Power Amplifier Gain Y axis range section Distortion percentage enters the range or maximum value of percentage distortions Num decades chooses number of decades below maximum value that are shown in the log plot X axis range section High V enters maximum RMS voltage shown on x axis Low V enters minimum RMS voltage shown on x axis Every graph curve can be set as an overlay curve An example is shown in Fig 3 3 That figure also shows dialog box Distortion Overlays that serves as an overlay manager Manipulation with overlays is the same as with overlays in main window described in the Section 2 6 40 STEPS User Manual DIN IMD 250Hz 8kHz gt Figure 3 3 Distortion graph and Distortion overlay manager 41 m a a gi jah s EE p ew P
25. commands are 47 B W changes graph background color to black or white Copy copies graph to Windows clipboard Distortion Displacement mm peak i 18 0 9 0 16 0 3 0 14 0 7 0 12 0 6 0 10 0 5 0 8 0 4 0 6 0 3 0 4 0 2 0 2 0 1 0 0 0 0 0 0 0 1 6 3 2 4 8 6 4 8 0 Crsr 6 5V THD 16 4 Dx 6 2mm Voltage Vrms MD2 2 873647 MD3 4 9691 89 Fig 3 10 Example of measurement results For displacement measurement a laser sensor type Baumer OADM 2016441 S14F is used The Fig 3 10 shows results of measurement where dominant distortion type was harmonic distortion The comparison of displacement and THD curves shows that in this case Xmax 5mm Measurement data can be saved in file Two format are possible textual files and binary files that have name extension vdx 3 4 Loudspeaker Distortion Limited Maximum SPL Loudspeaker maximum SPL is a sound pressure level of sine signal that can be achieved under condition that THD of signal radiated from loudspeaker is below the user defined threshold usually 10 Important notice It is of great importance that user follow proposed measurement procedure otherwise measured loudspeaker can be severely damaged Here we work with high sound pressure It is recommended that you protect your ears Please use professional microphones that linearly transduce large sound pressure Figure 3 11 shows measurement setup A loudspeaker is driven by power amplifier that 1s connect
26. d two output channels treating them as a stereo left and right channels As ASIO support multichannel devices user has to choose in a dialog box Audio Device Setup which pair of channels will be used in STEPS 1 2 3 4 Note ARTA closes and releases ASIO driver when measurement stops but if driver needs long time to be loaded in memory ARTA keeps driver open all the time 18 Fs et m m p Q FPS ser Ma nuai wi het ww VW DOL E W a i i ci 2 3 Sound Card and Microphone Calibration Menu command Setup gt Calibrate devices opens the dialog box Soundcard and Microphone Calibration shown on Fig 2 13 Soundcard full scale output mY 1 Connect electronic voltmeter or scope on left output channel Soundcard full scale input mv 1 Connect sine generator with known output voltage on Microphone sensitivity mV Pa i Connect microphone on etrange to zv ka Channel Left T Channel 2 Generate sine 400Hz 2 Enter voltage peak or rms Preamp gain Qutput level 3dB r 500 mVrms 2 Attach sound calibrator 3 Enter voltmeter scope value 3 Estimate Peak Input mV Pressure Level 94 dB 1000 mV rms nf Estimated Current 3 Estimate Mic Sensitivity Estimate Peak Output mv 4 Estimate Peak Output mi Left 2000 2000 Estimated Current Right 2000 2000 Estimated Current 2000 2000 my Diff 0 O 5 5 mV Pa Accept Accept 48000 w Figure 2 13 Dialog
27. e is also called a level mode as STEPS actually shows level at the measured system output For both measurement modes the time relationship between the excitation signal and analyzed signals is illustrated in Fig 1 5 transient time pause transient time ay i s a x ay a x sy analyzed signal delay oe integration time Figure 1 5 Time relationship between the excitation signal and analyzed signals The user has to define several measurement parameters o range of frequencies for the excitation signal o frequency increment between two measurements in STEPS user chooses 1 6 1 12 1 24 or 1 48 octave frequency increment o I O delay in a measured system 1 e delay from loudspeaker to microphone o integration time for heterodyne filtering common values are from 100ms to Is o transient time that is necessary to reach a steady state condition in acoustical measurements if we want to measure the influence of reverberation the transient time should be greater than one fifth of the reverberation time o duration of pause between two successive sine bursts in acoustical measurements duration of intra burst pause should be greater than one fifth of the reverberation time Note the criteria that transient time should be greater than one fifth of the reverberation time assures that the magnitude error will be lower than 1dB The measurement procedure is as follows 1 Start measurements with burst of sine signal of kno
28. ed to the soundcard left output channel Power amplifier has volume control Output from the loudspeaker is recorded by microphone connected on soundcard left input channel Power amplifier output voltage scaled by resistive voltage divider R2 R1 R2 is recorded using soundcard right input channel Value of divider resistors depends on power amplifier rating For 200W amplifiers that has 40Vrms maximum output voltage we can use divider with RI 3900Q and R2 100Q and set probe gain of 100 4000 0 025 in Device Setup Right preamplifier gain edit box 48 STEPS User Manual power Right out amplifier loudspeaker microphone soundcard Right input EE Left input a preamplifier Figure 3 11 Hardware setup for measurement of distortion limited levels File Edit Measurement channel SPL Channel 10 00 Distortion limited level dBv Excitation JBV gt Measure excit voltage 0 00 0 00 rate Hz ehh Excitation sine range 20 00 20 00 10 00 10 00 THD limit 5 20 00 30 00 Start freg Hz 40 00 D Stop freq Hz 1000 50 00 50 00 Fr resolution 1 30ct v ais sooo 2d v 70 00 T0 00 Dynamic range 40dB s ody Power reduction factor 2 1000 90 00 Integration constants Transient time ms 100 Record 20 00 Figure 3 12 Distortion Limited Levels measurement window User has to set the testing sine frequency THD limit in level step 0 5 1 1 5 or 2 dB and adjust max
29. ency range Graph Setup xX pe Harmonic distortion levels TH Yo os Foe fF os T pet Figure 2 20 Graph setup The Graph Setup dialog box has following controls Dynamic range dB section Graph top enters the value of top graph magnitude Graph range enters the graph magnitude range Fit to graph top sets the graph top value from the current data Freq range Hz section High enters the highest frequency shown in Hz Low enters the lowest frequency shown in Hz View section Pressure units chooses dB re 20uPa V dB re 20uPa 2 83V or dB re 1Pa V units Plot type chooses Magnitude Phase Magnitude Phase or Magnitude Distortion plot Harmonics distortion levels section check boxes THD shows the level of the total harmonic distortion D2 shows the level of the second harmonic D3 shows the level of the third harmonic D4 shows the level of the fourth harmonic D5 shows the level of the fifth harmonic D6 shows the level of sixth plus higher order harmonics Default sets default values Update updates the current graph Note setup values can also be chosen by using the menu command View 28 2 8 2 Editing Graph Colors and Line Style We edit some graph values by using commands from menu Edit For changing the presentation of the graph we use following commands Colors and grid style Sets graph colors and grid plotting style Use thick pen Set
30. equency loudspeaker response in half space 27 and response in a full space 47 For a rectangular box that has front baffle width w and height h STEPS internally uses as approximation an equivalent squared box of width d w h w 3 LF Box Diffraction x W f Box form Spherical Baffle width cm 30 Baffle height cm so cca Figure 2 24 Dialog box LF Box Diffraction 32 Fig 2 25 shows an example of the measured near field loudspeaker response upper curve and estimated free field response bottom curve At very lower frequencies the level difference is 6dB FR Magnitude dB Viv 100 1000 10000 Cursor 20 2 Hz 32 63 dB Frequency Hz Figure 2 25 Near field loudspeaker response upper curve and 27 42 equalized response lower curve 2 9 Percentage Distortion Plot A common way to plot distortion frequency characteristics is in log log percentage distortion plot as shown in Figure 2 26 Figure shows distortion of small low quality multimedia loudspeaker We get this plot by clicking menu command View gt Percentage distortions or by clicking toolbar icon D l 33 STEPS User Manual EG Distortion Pri H F et 0 01 EEEE EEEE 20 50 100 200 500 1K 2K 5K 10k 20k t 1128Hz THD 45 63383 D2 4 20635 D3 45 43956 f Hz eroe e a zle aote or cm a Figure 2 26 The window for percentage distortion plot The log log graph can show six curves THD
31. for the difference in time and in samples between the cursor and the marker Buttons on the right pane serve as commands to Scroll the signal plot to Zoom plot in and out to change the Gain and vertical Offset Zoom ratio is shown above the upper right corner of the graph It is written as ratio p n where p means number of pixels used to draw n signal samples Maximal zoom is defined with ratio 8 1 normal zoom is defined with ratio 1 1 and minimal zoom is defined with ratio 1 m where m signal length graph width in pixels Zoom commands Up increases the zoom ratio 36 Down decreases the zoom ratio Min sets minimal zoom ratio to show almost all signal samples Max sets maximal zoom ratio by following these rules e If marker is set then all samples between the cursor and the marker will be shown with maximum possible zoom ratio e If the marker is switched off the plot is zoomed to ratio 1 1 or 8 1 with cursor position sets to first graph point or maximum ratio 8 1 if previous zoom ratio is lower or equal to 1 1 Gain commands Up increases the gain factor Down decreases the gain factor Min sets minimal gain factor Max sets maximal gain factor Offset commands Up increases the vertical offset Down decreases the vertical offset Null sets the vertical offset to zero Scroll commands Left scrolls the plot to the left Right scrolls the plot to the right The Channel combo box sh
32. harmonic component Steps can export data in three textual forms 1 Magnitude Phase commented TXT contains comments lines and lines with data frequency magnitude phase lt Steps info gt Start frequency 200 0 Stop frequency 20318 8 Frequency increment 1 12 octave Num frequency points 81 Num channels 2 Microphone not used lt Steps values gt dBV V Freq Hz Magn dB Phase deg 200 0 so 0 0 0 ge o il 0 0 ZAO oro Ni g 0 2o Fel Oz odi 0 0 2 Magnitude Phase plain TXT contains lines with data frequency magnitude phase 20070 Ove OVU ZL 20 0 SD 201 0 Ar My 9001 As 0 ZLE ONUL oD 3 Magnitude distortion has following form lt Steps info gt Start frequency 200 0 Stop frequency 20318 8 Frequency increment 1 12 octave Num frequency points 81 Num channels 2 Microphone not used lt Steps values gt dBV V Freq Hz Magn dB THD S Dist2 Dists 3 Dist4 ZOO 20 OOK 000072 0700015 0 0006 ZAI O01 OsO00G2 0 00019 O70006 Ve ENS Bi 0 00083 0 000128 G 00069 Zoka O01 OOOO OOOO 20 0 0065 ZO U Oca OLOVO OZ00027 O200070 ZO TO 0 OJODOTT O00019 0200063 27 2 8 Graph Setup and Editing 2 8 1 Graph Setup The menu command Setup gt Graph Setup or pressing button Set in right control bar or right clicking mouse in the plot area opens the dialog box Graph Setup Fig 2 20 Use this dialog box to set the plot type and adjust graph magnitude and frequ
33. if there is no noise and if the integration time T is equal to the multiple of 1 0 In that case the integral term of other_harmonics is equal to the zero and we estimate the amplitude and the phase by the expression A 2 Re c Im c DE arctan e c In the presence of the noise we have a biased estimation but that bias will be very small if we apply a long integration time that gives a small bandwidth of a heterodyne filter To calculate the Fourier series integral we can use some numerical integration algorithm the simplest is the Discrete Fourier Transform In a discrete domain the condition that integration time is a multiple of a sinusoid period cannot be fulfilled and we have a leakage in the spectral estimation The usual technique to suppress the leakage 1s to apply the window function w t well known are Hanning Blackman or Kaiser window The STEPS uses the Kaiser window and a special form of DFT algorithm called Goertzel algorithm The STEPS shows the distortion of sinusoidal signal induced by n th harmonic component as a percentage of harmonic distortion or a harmonic distortion level in dB Da 100 A A1 percentage of n th harmonic distortion Da dB 20 log A A1 distortion level of n th harmonic component The STEPS shows the Total Harmonic Distortion of a sinusoidal signal as THD 100 sqrt A2 A3 A127 Aq THD dB 10 log A2 A3 A12 A1 Fig 1 4
34. ill be saved The button Cancel cancels the copy operation Enter text that will be drawn on the bottom of the graph copy s Bitmap size Current screen size Copy to Clipboard Add filename and date Add text Cancel Figure 2 5 Dialog box Copy Save Image with Extended Information 10 2 1 STEPS Menus Here is a brief explanation of all Steps menus File New Creates a new file Open Opens an existing file HSW Save Saves the file with current name Save As Saves the file under a new name Export ASCII Exports the file in ASCII format Magnitude Phase commented TXT text file with comment text and with rows containing frequency Hz magnitude dB and phase deg Magnitude Phase plain FRD text file with rows containing frequency Hz magnitude dB phase deg Magnitude distortion T XT text file with rows containing frequency Hz and percentage distortions for THD 2nd 3rd and higher order harmonics Magnitude Phase CSV CVS Excel file containing frequency Hz magnitude dB and phase deg Magnitude distortion CSV CVS Excel file containing frequency Hz and percentage distortions for THD 2nd 3rd and higher order harmonics File Info shows information of currently opened file Recent File opens a recently opened file Exit exits program Overlay Set sets the current measured FR curve as an overlay Manage overlays ope
35. imum dynamic range 30 36 40 or 46 dB for chosen power amplifier For example if user choose dynamic range of 30 dB then testing will be done for soundcard output levels from 31 to 1 dBFS Before the measurement user is responsible to adjust power amplifier volume control so that generator level of 31 dBFS gives power amplifier output voltage that is 31 dB or 35 5 times lower 49 that amplifier maximum voltage 1 e for 200 W amplifier with maximum output rms voltage of 40 V user have to set volume control to obtain 40 35 5 1 12Vrms at amplifier output when generator level is 31dBFS For this purpose user can use dialog box Measurement Setup as level controlled sine signal generator If user does not set amplifier volume control properly there is a chance of pushing power amplifier output to clipping If STEPS works in dual channel mode the clipping is checked and reported to user Window Distortion Limited Levels has following controls Measurement channels section SPL channel chooses the microphone input channel Measure excit voltage check to record power amplifier output and amplifier clipping Sampling rate Hz chooses the current sampling frequency Excitation sine range section THD limit enters distortion threshold Start freq Hz enters starting frequency Stop freq Hz enters highest frequency Freq resolution chooses fractional octave frequency increment in one measurement step Level s
36. l RMS voltage value Stop value V rms enters ending maximal RMS voltage value in parenthesis a maximum possible value for a given Power Amplifier Gain is shown Use logarithmic step check box to uses logarithmically spaced amplitudes Number of steps enters number of steps of stepped amplitudes 42 Power reduction duty cycle enters number in the range 2 to 50 which represents the ratio of the duration of generated signal pause and duration of generated signal signal in one step It is proportional the ratio of peak signal power during signal generation to total output signal power Integration constants section Intg time ms enters integration time used for RMS estimation Transient time ms enters time that is needed for system to reach the steady state It can be from several ms to more than 1000 ms The larger value are appropriate for measuring audio compressors or circuits with automatic gain control Bottom buttons Record starts the measurement If pressed during the measurement this button stops the measurement Copy copies the current graph to the clipboard in bmp format B W changes the current graph background color to black or white Setup opens the dialog for Graph setup Overlay opens the dialog for overlay manipulations Cancel closes the window and discards current measurement setup OK closes the window and saves the current measurement setup The window has two menu items File com
37. lowing previous definition STEPS gives user interface for practical measurement procedure that is being executed as follows 1 Mount the driver in a free field and measure resonance frequency fs of the driver 2 Use measurement setup with two sensors microphone that is placed in a driver near field connect to the one input channel and optical laser devices that can measure voice coil displacement connect to the other input channel 3 Connect input of a driver s power amplifier to the soundcard left output channel and excite the driver with a two tone signal f fs and f 2 8 5fs and with amplitude ratio U 4U gt and perform a series of stepped amplitude measurements with Ustart lt U lt Uend 4 Measure the peak displacement spectral component D fi and spectral content of the sound pressure in the near field versus amplitude U For each amplitude U determine amplitudes of fundamental tones P f1 and P 2 harmonic components P k f with k 2 3 K and total harmonic distortions 44 PFY PGf 4 PKF MODRI ye so BALL TTT Pf PQPf PGP o P Kf second order and third order modulation distortions MD oP 2 t f PY A MD 09 f 2 test PO 29 PCa P 5 Search for the minimal value of the excitation voltage Uz0 in the range Ustart lt Uro lt Uend where either the THD MD2 or MD3 respectively equals 10 6 Find the peak voice coil displacement X
38. mands are Open retrieves data from binary vsl file Save saves data in binary vsl file Export saves data in textual files in plain ASCII or Excel CSV format Edit commands are B W changes graph background color to black or white Copy copies graph in Windows clipboard The right mouse click in the graph area or click on button Setup opens the dialog box Linearity graph setup It is shown in Fig 3 5 Linearity graph setup x Show relative M dBvN Update Default Cancel Figure 3 5 Dialog box Linearity graph setup Dialog box Linearity graph setup has following controls Axis Type section Show Log V or dBV check box to set logarithmic or dB Y axis Show relative dB V V check box to use linearity function as Y X vs X Y axis range section Ymax dBV enters maximum of shown level or transfer function depends on the state of the check box Show relative Ymin dBV enters minimum of shown level or transfer function depends on the state of the check box Show relative 43 X axis range section Xmax dBV enters maximum of shown input level Xmin dBV enters minimum of shown input level 3 3 Displacement and Distortions Testing The estimation of a peak acoustic power which can be generated from some loudspeaker driver is based on the loudspeaker voice coil peak displacement usually denoted as Xmax Here a method for measuring Xmax Will be presented
39. max as a displacement that correspond to the amplitude U10 soundcard Right input power amplifier microphone loudspeaker preamplifier Fig 3 6 Two channel measurement setup for loudspeaker pressure response and voice coil displacement measurements The excitation signal is a stepped amplitude two tone signal Figure 3 7 Positioning of laser displacement sensor and microphone 45 3 3 3 STEPS User Interface for Measurement of Xmax For the simultaneous measurement of loudspeaker distortions and voice coil displacement the STEPS gives us a user interface in the window Displacement Distortion Function shown in Fig 3 8 This window is opened by the menu command Record gt Loudspeaker displacement distortion ES Distortons and Displacement untitled vdx j hn u Oo x File Edit Measurement channels Response channel Left Distortion Displacement mm peak Sampling rate Hz 48000 0 Ez 10 0 Use displacement sensor on other channel Sensitivity mV mm 30 10 0 Start value V rms Stop value V rms max lt 0 520V Number of steps 0 1 0 01 I Logarithmic step increment THD break value 54 15 Sine frequencies Frequency fi Hz 50 M Use f2 8 5f1 Ul 4U2 0 01 0 001 0 001 0 0001 0 1 0 2 0 5 1 0 2 0 5 0 10 0 Voltage Vrms Integration constants Integration time ms 300 Transient time ms 50 Reawd
40. me to 3dB 4 Enter the value of signal generator voltage in the edit box but only if it differs from value used during output channel calibration 2 3 1 5 Press the button Estimate Peak Input mV 6 If you are satisfied with the measurement press the button Accept and estimated value will become the current value of the LineIn Sensitivity 7 Repeat 1 6 for the right input channel Note This procedure is recommended as it guarantees that you can connect the soundcard in loopback mode If you want to calibrate input channels with input volume set to maximum many soundcards require a reduction of the level of the output channel 2 3 3 Calibration of the Microphone To calibrate the microphone you must have a sound calibrator Then Connect the microphone preamplifier to the soundcard input left or right Enter the preamplifier gain Attach the sound calibrator on the microphone Press the button Estimate mic sensitivity If you are satisfied with a measurement press the button Accept a e Note If you don t know the preamplifier gain you can set some arbitrary gain value but that value must be used as a preamplifier gain in the Audio Devices Setup dialog box 2 3 4 Frequency Response Compensation The quality of measurements depends on the quality of used sensors 1 e microphones It is possible to enter frequency response of sensor in STEPS and make the compensation of their frequency response by
41. n stepped amplitude mode STEPS can measure and graphically show three functions 1 Distortion vs amplitude harmonic and intermodulation distortions as a function of signal amplitude 2 Linearity function system output or system gain as a function of the input excitation amplitude 3 Loudspeaker displacement distortion combined measurement of displacement with optical laser device and distortion with microphone 4 Loudspeaker distortion limited maximum SPL in user defined frequency range First two type of measurements are primary targeted to measurements of power amplifiers audio compressors and automatic gain control systems while third type of measurement is for measurement of loudspeaker response 3 1 Distortion vs Amplitude Testing For the Distortion vs amplitude testing the user interface is given in the window Distortion vs amplitude shown in Fig 3 1 This window is opened by the menu command Record gt Distortion vs amplitude EE Distortion vs amplitude untitled vsd l Z iol x File Edit General distortion measurement a Distortion THD 100 0 g I Response channel Left E P Sampling 48000 7 S rate Hz 48000 10 0 Excitation sine voltage range Frequency Hz 1000 mj Start value V rms 0 1 l 0 1 Stop value V rms max lt 1 967V Use logarithmic steps W 0 01 Number of steps 10 Integration constants 0 004 300 0 1 0 2 0 5 1 0 Intg time ms i V
42. na 48 1 Introduction The STEPS is a program for frequency response measurement using a heterodyned stepped sine technique Compared to the Fourier analyzer that uses a random noise excitation this technique gives a larger dynamic range at least 30dB but measurements are much slower This program is also useful for measuring harmonic distortions as it estimates the linear part of the system response and the magnitude of distorted sine harmonics 1 1 Requirements Minimum requirements to use the STEPS are o Operating systems Windows XP Vista 7 8 o Processor class Pentium clock frequency 600 MHz or higher memory 256M for Windows 2000 XP or 2MB for Vista Windows 7 o Full duplex soundcard with synchronous clock for AD and DA converters o WDM or ASIO soundcard driver ASIO is trademark and software of Steinberg Media Technologies GmbH The Installation of this software is easy use ARTA installation program or just copy the program steps exe and the help file steps chm in some folder and make a shortcut to it All registry data will be automatically saved at the first program execution Files with extension HSW are registered to be opened with the program STEPS They contain the frequency response data Results of measurements can also be saved as textual ASCII formatted files The STEPS does not output graphs to the printer instead all graphs can be copied to the Windows Clipboard and pasted to other Windows applicatio
43. ns 1 2 Measurement Hardware Setup In this document we refer to following measurement setups 1 Dual channel measurement setup 2 Single channel measurement setup The general measurement setup for the system testing is shown in Fig 1 1 The soundcard left line output channel is used as a signal generator output The left line input is used to measure a D U T output voltage and the right line input is used to measure a D U T input voltage In a single channel setup only a D U T output voltage is recorded The setup for acoustical measurements is shown in Fig 1 2 STEPS User Manual left in output right in Not connected in single channel setup right out Signal generator souncard Figure 1 1 General measurement setup for the system response testing mic preamp ee eee ee eee right in voltage probe right out left out ower amplifier soundcard P P Figure 1 2 Measurement setup for acoustical measurements To protect the soundcard input form large voltage that is generated at a power amplifier output it is recommended to use the voltage probe circuit with Zener diodes as shown on Fig 1 3 Values of resistors RI and R2 have to be chosen for arbitrary attenuation 1 e R1 8200 and R2 910 ohms gives probe with 20 7dB 0 0923 attenuation if the soundcard has usual input impedance 10kQ Ina single channel mode this probe is not connected Power A Sound Amplifier Card Output
44. ns the Overlay Manager dialog box for editing of the overlay s list Delete all deletes all overlays Delete last deletes last entered overlay overlays Load loads an overlay from STEPS hsw file Load impedance overlay loads impedance overlay from zma or lim file Delete impedance overlay deletes loaded impedance overlays Edit gt Undo undoes last state Copy copies the graph bitmap and user defined text to the clipboard or saves that image to the file Colors and grid style sets graph colors and grid plotting style B W Color changes the background color to black or white Use thick pen sets pen style to draw thicker lines Smooth Magnitude Power smoothes magnitude in band 1 1 octave 1 2 octave 1 3 octave Scale level scales the magnitude level LF box diffraction scales the frequency response with response of loudspeaker box LF diffraction Cut below cursor cuts plotted points below the cursor position 11 Cut above cursor cuts plotted points above the cursor position View Toolbar shows or hides the toolbar Status Bar shows or hides the status bar Fit graph top fits graph top margin to maximum magnitude Time Record shows the time record of the last recorded signal Percentage distortion shows window with log log plot of percentage distortion Magnitude shows the magnitude Phase shows the phase Magnitude Phase shows the magnitude and the phase Magnitude Disto
45. o copy or save the graph picture that is shown inside the window user needs to simultaneously press keys Ctrl C or activate the menu command Edit gt Copy or press appropriate Copy button In the main window toolbar the Copy button is shown as toolbar icon The Copy command opens the dialog box Copy Save Image with Extended Information shown in Figure 2 5 Here user has to setup following options 1 2 3 4 5 By using the combo box above OK button user chooses one of three modes of saving the image Copy to Clipboard Save to File and Save to File Copy to Clipboard In the Edit box user optionally enters the text that will be appended at the bottom of the graph Check box Add filename and date enables adding text to the graph that shows file name date and time Check box Save text enables saving entered text for the next copy operation Bitmap size is chosen by selecting one of following combo box items Current screen size variable width and height option Smallest 400 pts fixed graph width 400 points Small 512 pts fixed graph width 512 points Medium 600 pts fixed graph width 600 points Large 800 pts fixed graph width 800 points Largest 1024 pts fixed graph width 1024 points The options with fixed width give graphs with the aspect ratio 3 2 The button OK copies the graph to the system clipboard or opens dialog to enter name of file in which picture w
46. oltage V rms Transient time ms 50 ner ew Copy Setup Overlay Cancel ox E Figure 3 1 Distortion vs amplitude window 38 Measurement of distortions is a single channel measurement We measure system response to sine signal and estimate distortions THD or IMD from that signal the same way as we do in the swept sine mode The measured system must be excited with the STEPS sine or two sine signal generator The graph shows the percentage of distortion as a function of the measured signal RMS voltage Alternatively the graph can show the percentage of distortion as a function of the estimated value of RMS voltage on the output of the power amplifier It is a product of the playback lineout RMS value and Power Amplifier Gain as defined in Audio Devices Setup Dialog The measurement setup is defined in three sections General distortion measurement section First Combo box is used to define what type of distortions will be measured THD total harmonic distortion with user defined excitation frequency DIN IMD with two sine excitation on 250 Hz and 8 kHz SMPTE IMD with two sine excitation on 60 Hz and 7 kHz CCIF IMD with two sine excitation on 13 and 14 kHz CCIF IMD with two sine excitation on 19 and 20 kHz Response channel chooses input on Left or Right channel Sampling rate chooses sampling rate in Hz Excitation sine voltage range section Frequency Hz enters frequency for measuring THD Start val
47. ows the currently used channel left or right You can also use following shortcut keys Up and Down to change the gain Ctrl Up and Ctrl Down to change the vertical offset Left and Ctrl Left to scroll the plot left Right and Ctrl Right to scroll the plot right Shift Left and Shift Right to move the cursor left and right PgUp and PgDown to change the zoom factor Shortcut keys are active if graph window has focus The focus is set by clicking the mouse in the graph area Dragging the mouse in the label area scrolls the plot horizontally and vertically Double clicking of the left mouse button in the time axis area toggles the time sample position labeling Menu commands are File Export ASCII saves time and amplitude data in textual file Info opens message box that shows the signal RMS value and crest factor If the marker is set the RMS value is determined for the gated part of the signal Edit Copy copies graph window to clipboard BW background color changes background color to black or white 37 3 Using STEPS for stepped amplitude testing The stepped amplitude testing is a measurement method in which we measure system response and distortion as a function of the excitation signal amplitude The excitation signal is the sine or two sine signal with a user defined frequency The amplitude of the excitation signal is changing from lowest to highest value in a predefined number of measurement steps I
48. peated for logarithmically spaced frequencies and results shown as a magnitude phase magnitude phase or magnitude distortion plot To change the plot type ma press one of following icons Meg Ph MiP M D Notes You can stop measurements prematurely by clicking the menu Record gt Stop or by clicking the toolbar icon You can copy the graph bitmap to the clipboard by clicking the menu Edit gt Copy or by clicking the toolbar icon The quality of measurement depends on the quality of a soundcard Fig 2 16 shows the frequency response plot of a high quality soundcard EWX 24 96 It is obvious that STEPS can measure distortions that are more than 120 dB below the maximum signal level but actual distortion resolution depends on the quality of the soundcard used Magnitude dBW O 20 0 L F 40 0 S 60 0 60 0 100 0 m D3 120 0 aD 140 0 m liagn 20 50 100 200 500 1k 2k SK 10k 20k f 1208 1 Hz Magn 5 79 dB HZ D2 107 94 D3 112 12 dB Figure 2 16 Typical frequency response plot of a high quality soundcard The bottom grey curve shows second harmonic distortion and the red curve shows the third harmonic distortion 23 In acoustical measurement we usually measure much higher level of harmonic distortion Figure 2 17 shows the frequency response of a small low quality multimedia loudspeaker FR magnitude dB re 0uPan 100 0 90 0 50 0 r0 0 60 0 50 0 40 0 30 0 20 0 10 0 0 0 20 50 100 200 500 1K
49. rtion shows the magnitude 2nd and 3rd harmonic distortion Sound pressure units sets the sound pressure unit if the microphone input is enabled to dB re 20uPa V dB re 20uPa 2 83V dB re 1Pa V Record Run starts recording measurement Stop stops recording measurement Distortion vs amplitude opens dialog for stepped amplitude distortion testing Linearity function opens dialog for stepped amplitude I O linearity testing Distortions and Displacement opens dialog for stepped amplitude measurement of displacement Loudspeaker distortion limited SPL opens dialog for measurement of distortion limited SPL Setup Audio devices sets current input and output devices Calibrate devices calibrates the soundcard and the microphone FR compensation gets dialog box for frequency response compensation Measurements configures measurements Graph sets graph margins CSV format sets decimal separator character for CSV files dot or comma Help User Manual shows the help file Registration shows license registration info About shows information about the STEPS version Useful shortcuts keys are Up and Down keys change the top graph margin Left and Right keys move the cursor left and right Ctrl S key saves the file Ctrl N key makes a new file Ctrl O key opens the file Ctrl C key copies the graph bitmap and user defined text to the clipboard or saves that image to the file Ctrl
50. s dialog for entering the Scale in dB for shifting the current level The right mouse click in the graph area or click on button Setup opens the dialog box Graph Margins It is shown in Fig 3 13 Setup of Power reduction factor is very important as it can save us from burning the loudspeaker If loudspeaker has declared long term power P and testing will be done with power amplifier that can generate power Pmax We must set power reduction factor to value Pmax P 50 STEPS User Manual When testing tweeters use even larger power reduction factor It is best that you assume that tweeter can withstand only 1 2 W of continuous power Graph Margins x SPL range dB re 20uPa Top dB za Frequency range High Hz 5000 M Show excitation voltage Update Default Cancel Figure 3 13 Dialog box Graph Margins Dialog box Graph Margins has following controls Frequency range section High Hz enters maximum frequency for right graph margin Low Hz enters minimum frequency for left graph margin SPL range dB re 20uPa section Top dB enters top margin in dB for SPL graph Range dB enters SPL graph range in dB Excitation Voltage dBV section Top dBV enters top margin for excitation voltage graph in dBV Range dBV enters graph range for excitation voltage in dBV Show excitation voltage check to show plot of excitation voltage in dBV 51
51. s pen style to draw thicker lines Graph colors can be changed in two ways First one is to change the color scheme from Black background mode to White background mode It can be done by clicking the menu View gt B W color or by clicking the toolbar icon The second way to change graph colors is user mode The user sets an arbitrary color for every graph element using the dialog box Color Setup shown in Fig 2 21 You activate it by clicking the menu Edit gt Colors and grid style The color setup is different for Black background mode and White background mode as shown in Fig 2 21 The magnitude curve uses the Plot pen 1 color the phase curve uses the Plot pen 2 color the harmonic distortion curves use Plot pen 2 to Plot pen 6 colors the THD curve uses the Overlay 8 color Clicking the left mouse button on a named color rectangle opens the standard Windows dialog box Color Fig 2 22 which serves as color picker Button Default restores default colors Note 1 If the check box All overlays with same color is checked all overlays will be plotted with same color Note 2 If the check box Dotted graph grid is checked the graph grid will be drawn in dotted style Graph grid style is defined with three options e If the check box Dotted graph grid is checked the graph grid in all types of graphs will be drawn in dotted style e Ifthe check box Add axes tick marks is checked FR and Spectrum graphs axes
52. shows the STEPS PC based measuring system The computer generated signal g after D A filtering with a transfer function D is applied to the test system that has a transfer function H Note that H represent the best linear fit of a possible nonlinear transfer function The generator noise is neglected The output from the test device together with an additive system noise n 1s acquired by the computer as a discrete signal sequence y The acquisition process implies the use of an antialiasing filter that has a transfer function A Noise D A filter n A D filter Figure 1 4 Block diagram of measuring system Note In acoustical measurements we neglect the influence of the generator noise and the noise in the input channel x as they are much smaller than the noise and distortions in the output channel y In a dual channel mode the input to the test device is acquired by the computer as a discrete signal sequence x The output from test device is acquired by the computer as a discrete signal sequence y Then the D U T frequency response is Magnitude H Magnitude Y Magnitude Xx Phase H Phase Y Phase X In a single channel mode signal at a system input is not measured and the signal g from computer memory is treated as a system excitation Now the estimated frequency response includes response of A D and D A filters Estimated Magnitude A Magnitude Y Magnitude DHAG Estimated Phase H Phase Y Phase DHAG This mod
53. signed int version version of file format int numpoints number of measured frequency points int numdist2 number of frequency points for D2 and THDs ine numdisto number of frequency points for D3 if version gt 0x0103 int numdist4 number of frequency points for D4 if version gt 0x0104 int numdisto number of frequency points for D5 Int numdiste number of frequency points for D6 int numchannels 1 or 2 channel measurement int resolution 24 or 48 of octave int smoothing 4 1 2 3 of octave int crspos Cursor position inc micused microphone 0 not used 1 used on output 2 used on input float micsens microphone sensitivity V Pa float frequency numpoints frequency in Hz float magnitude numpoints magnitude in dB float phase numpoints phase in degree float D2 n mdistz2 2nd harmonic levels in dB Float Di inundis I 3rd harmonic levels in dB if version gt 0x0103 float D4 numdist4 4th harmonic levels in dB if version gt 0x0104 Float D5 nu umdists 5th harmonic levels in dB float D6 numdist6 6th plus higher harmonic levels in dB float THD numdist2 THDs levels in dB int infotexr length char infolinfotext length user info text length user info text in bytes 26 Note Dn denotes n th harmonic distortion but D6 also contains power of 7th to 12th harmonic component In files version 103 D4 contains power of 7th to 12th
54. sition Menu commands Cut bellow cursor Cut above cursor and Scale level are normally used to combine two graphs one for the high frequency and the other for the low frequency response Menu command Scale level opens dialog box shown in Fig 2 23 in which user enters arbitrary level in dB to scale the magnitude response 31 Scale Magnitude Level x Enter value to scale magnitude in dB o 7 Also scale distortion level M Allowed range from 100 dB to 100 dB cont Kel Figure 2 23 Dialog box Scale Magnitude Level 2 8 4 Low Frequency Loudspeaker Box Diffraction Scaling Menu item LF box diffraction opens dialog box shown in Fig 2 24 In this dialog user enters the form of the box spherical squared or rectangular width and height of loudspeaker baffle These values are used for the definition of scaling transfer function W f that is used for the estimation of the free field response from the response of loudspeaker that is measured mounted in an infinite baffle or in the near field STEPS uses following expression for the LF diffraction scaling transfer function I Jf fo 2 IFT fo where fo 42 7 d for sphere of diameter d or fo 34 16 d for squared box of width d These values are obtained by numerically fitting transfer function W f with transfer function of a spherical loudspeaker box This transfer function is also called 27 47 equalizer as it gives the difference of low fr
55. tep dB chooses magnitude increment in one measurement step Dynamic range dB chooses maximum dynamic range for level testing 30 36 40 or 46 dB Power reduction factor 2 1000 enters number in the range 2 to 1000 which represents the ratio of the duration of generated signal pause and duration of generated signal in one step It is proportional the ratio of peak signal power during signal generation to total output signal power Integration constants section Transient time ms enters transient time as time necessary to reach the steady state condition integration time is always approximately equal to200ms Bottom Buttons Record starts the measurement If pressed during the measurement this button stops the measurement Copy copies the current graph to the clipboard in bmp format B W changes the current graph background color to black or white Setup opens the dialog for Graph setup Overlay opens the dialog for overlay manipulations Cancel closes the window and discards current measurement setup OK closes the window and saves the current measurement setup The window has two menu items File commands are Open retrieves data from binary spm file Save As saves data in binary spm file Export saves data in textual files in plain ASCII or Excel CSV format Edit commands are B W changes graph background color to black or white Copy copies graph in Windows clipboard Scale level Open
56. the left and the right input channels in dB Power amplifier gain If you connect the power amplifier to the line output and if you need calibrated results in single channel setup you have to enter the power amplifier voltage gain The best way to enter these values 1s to follow the calibration procedure as described in the next chapter In section Microphone Sensitivity enters the sensitivity of the microphone in mV Pa Microphone used check box if you use the microphone and want the plot to be scaled in dB re 20uPa or dB re 1Pa Also use combo box to choose the channel where the microphone is connected we strongly recommend to use the soundcard left channel as the microphone input channel The setup data may be saved and loaded by pressing the buttons Save setup and Load setup The setup files have the extension cal Important notice Please mute the line and microphone channels at the output mixer of the soundcard otherwise you might have a positive feedback during measurements If you use a professional audio soundcard switch off the direct or zero latency monitoring of the line inputs 2 2 1 WDM Audio Driver Setup for Windows 2000 XP After selection of the soundcard user has to disable mute line in and microphone inputs in output mixer In addition user has to select which input will be used for recording Line In or Microphone Mic For a standard PC soundcards the procedure is as follows 1
57. ue V rms enters starting minimal RMS voltage value Stop value V rms enters ending maximal RMS voltage value in parenthesis a maximum possible value for a given Power Amplifier Gain is shown Use logarithmic step check box to use logarithmically spaced amplitudes Number of steps enters number of steps of stepped amplitudes Integration constant section Intg time ms enters integration time used for RMS value estimation Transient time ms enters time that is needed for system to reach the steady state It can be from several ms to more than 1000 ms The larger value are appropriate for measuring audio compressors or circuits with automatic gain control Bottom buttons Record starts stops the measurement Copy copies the current graph to the clipboard in bmp format B W changes the current graph background color to black or white Setup opens the dialog for Graph setup Overlay opens the dialog for overlay manipulations Cancel closes the window and discards current measurement setup OK closes the window and saves the current measurement setup The window has two submenu items File and Edit File commands are Open retrieves data from binary vsl file Save saves data in binary vsl file Export saves data in textual files in plain ASCII or Excel CSV format Edit commands are B W changes graph background color to black or white Copy copies graph in Windows clip
58. wn frequency and e in single channel mode record the system output signal e in dual channel mode record system input and output signals 2 Acquire the steady state response after the transient and I O delay time Calculate the magnitude and the phase of the frequency response and magnitudes of harmonic distortions using Fourier transform 3 Increment the working frequency If that frequency is inside the user defined range wait for the predefined intra burst pause time and then repeat the step 1 For all above operations the STEPS has a suitable user interface That interface will be described in the next chapter STEPS User Manual 2 Using STEPS for stepped sine testing The Steps has the main program window as shown in Fig 2 1 A menu bar and a toolbar are on the top of the window and a status bar is on the bottom of the window The central part of the window shows the magnitude and the phase plot The control bar on right side of window is used for graph margin setup a Untitled hsw Steps O x Fie Overlay Edit View Record Setup Help amp clr fi m ss o mm GB Mag Ph mer MED 0 Top G ra Range G set FrHigh fo sie L 100 0dB R 100 0dB Stepped Sine Response Figure 2 1 Main program window Open Copy to Thick Stop Hardware Time View View file clipboard lines measurement selup record phase magn distortion 4 4 4 4 4 4 oi alr gt N m Mag Ph mP mo 0
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