Cedar DH2 manual - fra www.interstage.dk
Contents
1. 20 OPERATING THE CEDAR DH 21 piUgiepi qe 36 THE TUTORIAL TAPE a EA O A EE eee Eo Eo ENTERS 39 REMOTE CONTROL PROTOCOLS rtr nitate rhe EE eR ea pe Ee PEE EE eS ERE EE HRS 40 SELF TEST MODE D 43 DH 2 Rev 01 1 00 Page 2 November 30 2005 INTRODUCTION Thank you for purchasing the CEDAR DH 2 De Hisser Module This is the world s most advanced dedicated single ended noise removal unit and offers processing power and performance that could only previously be obtained using digital signal processors DSPs installed in desk top or larger computer systems such as CEDAR for Windows The De Hisser is designed for professional use although it will work perfectly well in a domestic environment and its features include the following Revolutionary noise removal algorithms No need for a Spectral Fingerprint The latest SERIES 2 CEDAR hardware e Digital Audio interfaces conforming to the AES EBU and SPDIF standards 24 bit input and output resolution when using AES EBU interfaces Three sample rates supported on digital inputs 32kHz 44 1kHz and 48kHz Two sample rates supported on analogue inputs 44 1kHz and 48kHz Balanced anal2. 10 Grounding or Polarisation The DH 2 should always be grounded or earthed 11 Power Cord Protection Power connectors should be routed so that they will not be walked on or pinched 12 Extended Periods of Non Use The DH 2 is not disconnected from the mains power as long as it is connected to the wall outlet even if the unit itself has been switched off Therefore if the DH 2 is not to be used for an extended period of time unplug the unit from the wall Pull the connector out by the plug never by the cord itself 13 Cleaning Clean only with a dry cloth NEVER use liquid cleaners such as alcohol or benzene on the DH 2 NEVER use abrasive pads on the DH 2 14 Damage Requiring Service The DH 2 should be returned to qualified service personnel when objects have fallen into the unit e liquid has been spilled into the unit the unit has been exposed to rain the unit fails to function or appears to operate abnormally the unit has been dropped or the case damaged 15 Servicing The user should not attempt to service the DH 2 beyond the instructions contained in the User s Manual All other servicing should be referred to qualified service personnel DH 2 Rev 01 Ver 1 00 Page 9 November 30 2005 SET UP 1 UNPACKING AND INSPECTION Be careful not to damage the DH 2 during unpacking Save the carton and all packing materials since you may need them to transport the DH 2 in the future In addition to the DH 2 a
3. ba p SERIES 2 Phones Input Level Output Attenuation Contrast Next remove crackle and buzz and reduce distortion if appropriate Digital 10 0dB 40 Bypass Pe e amp 8 B g 3 y Pos e Pre Post Enter 2 a CEDAR Azimuth corrector AZ 1 Ares SERIES 2 Phones Input Level Output Attenuation Contrast Then apply Azimuth Correction to material with phase and balance problems Digital e ox Power ous prn Bypass Page T Bypass 20 Level ree Pre Post Enter XUNG 2 CEDAR penisser 2 UT pacc gt Phones Input Level Output Attenuation Contrast SERIES 2 Finally apply noise reduction DH 2 Rev 01 Ver 1 00 Page 16 November 30 2005 LOCATION AND FUNCTION FRONT PANEL INDICATORS AND CONTROLS Refer to the Front Panel diagram 1 Power Switch 2 Input Signal Meters Left and Right Digital signal meters display the peak value of the selected input in dBOs The Over indicators will light if the input signal remains at full scale for four or more consecutive samples 3 Output Signal Meters Left and Right Calibrated signal
4. 01 Ver 1 00 Page 4 November 30 2005 because fc moves dynamically according to the signal content But such devices are limited for one thing they can only remove the noise which exists above fo which is itself an inaccurate representation of the highest frequencies contained in the genuine signal at any given time Secondly and in common with the simple low pass filter they have roll offs typically of the order 12dB octave or 6dB octave so they always allow some high frequencies through And thirdly even though the filters are designed to track the signal very quickly they cannot respond instantaneously so they tend to round off fast transients And because their raison d tre is to reduce the signal bandwidth they also tend to dull the genuine signal quite perceptibly So to summarise dynamic filters if you re not compromising the signal you may not be removing as much noise as you wish and if you re removing all the noise you re probably damaging the genuine signal Perhaps an alternative approach could give better results Instead of altering the frequency response of the signal to reduce the noise content how about changing the overall signal level in some way This isn t such a strange idea Consider if noise of a relatively constant amplitude is always present in a signal then if the total signal amplitude drops down to the noise level we can assume that no genuine signal is present While there are many flaws in this arg
5. 34 analogue 3 11 ATTEN 20 25 36 ATTEN 19 23 25 37 Attenuation 22 Attenuation 18 automation 42 Azimuth Correction 15 blanking plates 10 BRT 20 26 BRT 19 23 26 36 Bypass 17 20 21 BYPASS 36 CD 12 Checkbyte 34 40 Clear 23 27 CLEAR 21 36 clicks 36 CLOCK 29 30 Code 31 coding violations 31 Coldstart 30 Coldstart 20 42 command packet 40 Command Type 35 40 command value HIGH byte 40 compression 36 compression 26 compressor 22 Contrast 18 Control page 23 crackle 36 Crashed 34 DAC 3 DASH 12 DAT 12 19 DH 2 Rev 01 Ver 1 00 November 30 2005 De Clicking 15 De Crackling 15 default values 20 Dehiss2 15 De Hissing 15 De Scratching 15 DH 1 15 digital 11 Digital Output 20 Dithering 12 dithering 28 DSP 3 34 44 dynamic range 3 EIA rack 3 8 10 Emphasis 34 Enter 17 21 ENTER 42 Error 34 error detection 28 Error Level 23 31 Error Level 33 external clock 30 Function Keys 17 18 Function Keys 23 Ganging 23 26 glugging 25 36 Grounding 9 Headphone 17 Heat 8 HISS 1 15 humidity 10 I O 28 input 11 17 28 29 Input Level 21 Input Level 18 Input Source 20 J17 34 LCD Screen 17 LEVEL 20 25 LEVEL 19 23 25 36 37 limiter 22 LOCAL OFF 42 LOCAL ON 42 Lock 31 LOCK OUT 21 LTC 13 magnetic fields 10 Memory 44 METERS 43 MIDI 13 20 32 MIDI 3 42 MIDI CHANNE
6. are affected when you adjust LEVEL ATTEN and BRT The Ganging control has three modes Ganged Adjusting the controls affects the left and right channels identically unless such adjustment would move a channel beyond the limits of the scale In this mode the numeric readouts beneath the control bars displays the average value of the left and right channels values Left Only the left channel is affected and the numeric readouts beneath the control bars displays the left channel s values DH 2 Rev 01 Ver 1 00 Page 26 November 30 2005 Right Only the right channel is affected and the numeric readouts beneath the control bars displays the right channel s values Press F1 to toggle between modes Clear The settings of LEVEL ATTEN BRT and Ganging Controls may be returned to their default values simply by pressing CLEAR No other DH 2 controls or options are affected by this operation DH 2 Rev 01 Ver 1 00 Page 27 November 30 2005 PAGE 2 INPUT OUTPUT CONTROL PAGE I O CONTROL Access this page by repeatedly pressing the Dedicated Function Key PAGE until the CONTROL PAGE appears This page allows you to determine the input used the sampling frequency of the Analogue to Digital Converters the digital input error detection level and the digital output format Remember that all outputs are permanently active and that they do not require selecting but that the same digital data is supplied to both A
7. higher level of hiss will cause significant amounts of twittering Similarly ATTEN will require a greater value in order to reduce the hiss to an acceptable volume In short the track will require heavier processing because the noise is much more noticeable than on track 1 The following settings are average values which will work reasonably well for the whole track Light processing LEVEL 40 9 ATTEN 5 BRT 50 8 Heavier processing LEVEL 40 9 ATTEN 7 BRT 30 3 TRACK 3 RICHARD GRESKO This is a hissy tape recording from the 1970s The quality is reasonably good but like solo guitar the solo piano can be very difficult to restore without unacceptable side effects However and unlike track 1 the hiss is mostly constant so a lower LEVEL may be used without introducing twittering With mild ATTEN and typical values for BRT a very satisfactory result may be obtained Light processing LEVEL 21 0 ATTEN 3 BRT 50 8 Heavier processing LEVEL 21 0 ATTEN 5 BRT 30 8 DH 2 Rev 01 1 00 Page 39 November 30 2005 REMOTE CONTROL PROTOCOLS 1 RS232 RS232 is defined in the DH 2 as 9600 baud 8 bits data 1 stop bit No parity A command packet contains 6 bytes These are byte 1 channel number byte must be OxAF byte 2 Checkbyte Fixed must be 0x63 byte 3 command number see below byte 4 Command type Fixed 0x07 byte 5 command value HIGH byte byte 6 command value LOW byte The HIGH and LOW bytes togeth
8. meters display the peak value of all output signals The indicators will light if the output signal remains at full scale for four or more consecutive samples 4 LCD Screen Provides you with a variety of information and messages keeping you aware of what is currently happening in the DH 2 All the control screens of the DH 2 are displayed on the LCD screen Please refer to the following chapters for full instructions 5 Status Indicators Indicate the status of the analogue and digital inputs and whether the DH 2 is in idle or processing modes Also indicate the possible causes should the unit fail to function 6 Dedicated Function Keys Certain functions are fundamental to operating the DH 2 and these are controlled by the dedicated function keys Bypass Page Pre Post and Enter T a dial Spinwheel The a dial enables you to increase and decrease control values Please refer to the following chapters for full instructions 8 Headphone Socket For use with stereo headphones only Accepts a standard 1 4 stereo jack plug DO NOT use 2 conductor mono headphones with the DH 2 9 Headphone Level Control Use this to adjust for a satisfactory listening level This level control will not alter the signal level at any of the rear panel outputs DH 2 Rev 01 1 00 Page 17 November 30 2005 10 11 12 13 Input Level Control This control acts upon the analogue inputs only Use it to adjust the volume of i
9. part because the fingerprint is merely a snapshot of the random noise accurate only at the instant at which it is taken Because the noise content is constantly changing an unmodified subtractive algorithm will be deriving its result from inappropriate data Garbage in garbage out DH 2 Rev 01 Ver 1 00 Page 6 November 30 2005 These pitfalls have prompted much commercial and academic research and many companies and independent researchers have investigated enhancements designed to overcome them CEDAR Audio s developments are embodied in its product HISS2 which incorporates an algorithm that updates the noise fingerprint every 1 000 samples This allows the system to track variations in the noise content It also features algorithms that prevent the compression of incoming transients and that distinguish between true noise and for example reverberation tails of the genuine signal These and other features avoid many of the pitfalls of simple spectral subtraction and allow users to remove noise without undue damage to the genuine signal contained within the source But this system still requires a noise fingerprint whether captured from the signal or created by arbitrary means Consequently the user interface is complex and the system cannot be implemented in a stand alone box The greatest simplification of this interface requires an algorithm capable of autonomous determination of the noise content Such methods are the subje
10. 44 1kHz on Coldstart EXTERNAL SYNCHRONISATION The DH 2 clock may be synchronised to either the AES EBU input or the SPDIF input Connecting a valid digital input to either of these and selecting AES Sync or SPDIF Sync as appropriate will lock the DH 2 to the external clock If the external clock falls within the acceptable ranges of each of the standard sample rates 44 1kHz 48kHz 32kHz the clock frequency will be shown on the LEDs If the external clock lies outside these ranges the DH 2 will still function and good audio will be produced at the analogue output Whether the digital output will be usable will then be determined by the flexibility of other devices in the digital audio chain To toggle between AES Sync and SPDIF Sync and also between the internal 44 1kHz and 48kHz sampling frequencies press the Function Key marked C on the LCD screen Note If external synchronisation is requested but no valid signal is detected at the appropriate digital input the DIGITAL LED will flash to indicate the error DH 2 Rev 01 Ver 1 00 Page 30 November 30 2005 RECEIVER ERROR LEVEL INPUT SOURCE AES EBU or SPDIF The DH 2 features sophisticated software which detects and analyses both fatal and non fatal errors in the incoming digital audio data You may select one of four error levels which will cause the front panel DIGITAL LED to flash if the incoming data contains an error equal to or worse than the selected
11. CEDAR Professional Hardware Systems DH 2 De Hisser Digital Audio Restoration System SERIES 2 Level rS over EE Over By 4BkHz lypass age B gm E v S z zs Pot 6 Pre Post Enter mu 2 ys CEDAR DH2 i as o deb mm NN M M mt ake SERIES 2 O OWNER S MANUAL 1996 CEDAR Audio Ltd DH 2 Rev 01 Ver 1 00 Page 1 November 30 2005 TABLE OF CONTENTS hhmiebjleje M 3 THE BACKGROUND TO CEDAR NOISE REMOVAL eeeeeeee eee en teens teen en etatn toes ene tatnen ene toto tnos ete tnn 4 SAFETY xditexd e Lr 8 SETUP eee ertet er Rega re eee 10 c M 11 SAMPLE INSTALLATION IDEAS erret enel terae eae Teesta Ee ny eR rene enun 14 A GUIDE TO RESTORATION PROCESSING eeeeeeeeee reete teen en etn tatnen enata inen 15 LOCATION AND FUNCTION OF FRONT PANEL INDICATORS AND CONTROLS 17 QUICK TOUR quoc A 19 WARMSTART AND COLDSTART eeeeeeee enses ente enne tnt
12. ES EBU and SPDIF outputs The data format will therefore only be appropriate for one digital output at any given time There are three options in the I O Control Page A DIGITAL OUTPUT This option defaults to AES EBU To toggle between the two output modes AES EBU and SPDIF press the Function Key marked A on the LCD screen AES EBU FORMAT When AES EBU is selected both the phono and XLR connectors will carry AES EBU specification audio data You should patch the output from the XLR connectors to your recording device The DH 2 features 24 bit input and output resolution when AES EBU is selected SPDIF FORMAT When SPDIF is selected both the phono and XLR connectors will carry SPDIF specification audio data You should patch the output from the phono connectors to your recording device TPDF dithering will be applied to the digital data at the 16 bit level and is always applied at the analogue output DH 2 Rev 01 Ver 1 00 Page 28 November 30 2005 INPUT SOURCE There are three input sources AES EBU SPDIF and ANALOGUE To toggle between the input sources press the Function Key marked B on the LCD screen The Status LEDs will indicate the inputs selected and the sample rate received digital or selected for conversion analogue SAMPLE RATE OF INCOMING DIGITAL SIGNAL When the DH 2 is switched to receive digital audio data the DIGITAL LED will be lit and the front panel LEDs will indicate the s
13. L 32 MIDI DUMP 42 MIDI DUMP 21 noise pumping 26 output 11 12 17 22 output format 28 Over 17 Page 17 21 peak 17 Phase EX 15 phono 28 polarity 11 POST 36 Power connectors 9 power supply 8 Pre Post 17 20 21 Receiver Error Level 20 remote control 32 resolution 12 RS232 32 RS232 3 13 40 RS232 Protocol 32 Running 34 Sample Rate 34 sample rate 29 sampling frequency 28 self test 43 servicing 9 SMPTE EBU 32 SMPTE EBU 3 13 32 SPDIF 28 SPDIF 11 12 28 30 31 SPDIF Sync 30 Spectral Fingerprint 3 Spinwheel 17 Status Indicators 17 Status Page 23 STATUS PAGE 33 SYNCHRONISATION 30 Timecode 32 42 timecode 3 13 Timed Out 34 TPDF 12 28 Trans 31 twittering 25 36 Unknown 34 Valid 31 Ventilation 8 VITC 13 VU meters 3 Warmstart 20 42 XLR 12 28 Page 45 CEDAR DH 2 Designed and Manufactured by CEDAR Audio Ltd 9 Clifton Court Cambridge CB1 4BN Tel 44 0 1223 414117 Fax 44 0 1223 414118 DH 2 Rev 01 Ver 1 00 Page 46 November 30 2005
14. TTEN Attenuation Control F4 BRT Brightness Control F5 Clear The controls and therefore the DH 2 itself act in the following manner Brightness Level Attenuation 3 Tonal Transient Ambience Gain Analysis Analysis Analysis Structure Noise Attenuation Reduction Control Pm Output Input Level Output Level Meters Meters Input Figure 1 The DH 2 process overview and the stages at which the CONTROL PAGE controls modify the signal DH 2 Rev 01 Ver 1 00 Page 23 November 30 2005 You can optimise the beneficial effect of the DH 2 by setting each of these controls appropriately They are now described in turn DH 2 Rev 01 Ver 1 00 Page 24 November 30 2005 LEVEL The LEVEL control is used to give the DH 2 algorithm a rough idea of the amount of noise present in any given signal This is the most sensitive and important control on the DH 2 and incorrect use will result in sub standard results and or unwanted side effects LEVEL too low The DH 2 will not remove all the noise and especially at high brightness levels will generate an artefact from residual noise pulses let through by the process This is often described as twittering LEVEL too high Some low level signal will be treated as noise and will be attenuated This results in compression and an artefact called glugging LEVEL
15. TTEN to a level defined by the material and your taste However you will notice that if LEVEL is high you can only reduce ATTEN by a few dBs before the on set of side effects such as loss of transients and loss of high frequencies If LEVEL is low ATTEN can be reduced further but with reduced effect As you reduce ATTEN you may notice one of two detrimental effects occurring e If there were twitters present after step 3 and if you reduce ATTEN beyond the optimal level for the specific material being processed the twitters may be re introduced as a form of high frequency noise modulation If there was loss of high frequencies present after step 3 you will notice that this loss is gradually re introduced as you decrease ATTEN It is unlikely that the values of the three controls are already optimised so you should now return to step 3 and attempt to find a better value for LEVEL Having done this you will no doubt wish to modify BRT and ATTEN further Continued fine tuning of these controls will lead to excellent noise removal with few or no side effects However the DH 2 is not a magic wand and it may not be possible to restore some especially badly degraded material beyond a certain point Only experience will enable you to judge whether you DH 2 Rev 01 Ver 1 00 Page 37 November 30 2005 have removed as much noise as possible without unacceptable consequences In general if the value of the Attenuation
16. ample rate of the digital signal presented to the inputs neither 44 1 nor 48 kHz LED lit 44 1 kHz LED lit 48 kHz LED lit 32 kHz signal presented to inputs 44 1 kHz signal presented to inputs 48 kHz signal presented to inputs s CLOCK DETECTION If the DH 2 fails to detect a digital signal within the following limits the 44 1kHz and 48kHz LEDs will flash continually This will be irrespective of any other system settings Acceptable ranges 44 1kHz 4 48kHz 496 32kHz 4 SAMPLE RATE OF A TO D CONVERTERS When the DH 2 is switched to receive analogue audio data the DIGITAL LED will not be lit and the front panel LEDs will indicate the sample rate of the analogue to digital converters The ADCs in the DH 2 do not offer a 32kHz option unless synchronised to an external 32kHz source DH 2 Rev 01 Ver 1 00 Page 29 November 30 2005 C A TO D FREQUENCY INPUT SOURCE ANALOGUE The ADC frequency may be selected by two fundamentally different methods The first is to select one of the internal clock frequencies available the second is to control the sample rate by using an external clock INTERNAL CLOCK FREQUENCIES To toggle between the DH 2 s internal 44 1kHz and 48kHz sampling frequencies and between AES Sync and SPDIF Sync see below press the Function Key marked C on the LCD screen The change in frequency will be shown on screen and also by the Status LEDs Note The sampling frequency reverts to
17. between genuine signal and noise They still act upon the inaccurate assumption that if the total signal level approaches its noise floor all that is present is broadband noise Consequently even the most sophisticated downwards expanders and dynamic filters remove some of the genuine signal Furthermore the poor band separation filters typically of the order 6dB oct or 12dB oct severely limit performance The consequences of these problems are well understood and largely unavoidable loss of high frequencies loss of ambience and degradation of hard transients All the methods so far described use filters gain controls or a combination of both to achieve their results Whether implemented in either the analogue or digital domain all such filters and gain controls are ratio devices that is if at any given frequency you remove half the power of the noise you remove half the power of the signal if you remove 3 4 of the noise you remove 3 4 of the signal and so on Consider now a signal that has at a given frequency 100 units of volume on some arbitrary scale By measuring the noise content of that signal during an otherwise silent passage you can determine that there are say 20 units of noise present at that frequency It should be possible to remove this noise by removing 20 of the signal But what if a moment later the total volume of the signal drops to 40 units An analogue filter removing 20 of the signal in the sa
18. ct of much on going research although as yet only two have been proved sufficiently accurate to be incorporated within commercial products Developed by CEDAR these algorithms make possible a stand alone module that dispenses with the user derived noise fingerprint The algorithm will itself analyse the noise content of the signal and apply an automated noise reduction process Further development of this process has led to an enhanced computer based software module called Dehiss2 which may be found in the CEDAR for Windows suite of audio restoration products as well as the latest DH 2 De Hisser Dolby and dbx are trademarks of their respective manufacturers DH 2 Rev 01 Ver 1 00 Page 7 November 30 2005 SAFETY INSTRUCTIONS CAUTION 1 Read all of these instructions All safety and operating instructions should be read before the DH 2 is operated Save these instructions for future reference Follow all warnings and instructions Water and Moisture The DH 2 should not be used near water and must not be exposed to rain or moisture If the DH 2 is brought directly from a cold environment into a warm one moisture may condense inside the unit This in itself will not damage the DH 2 but may cause hazardous electrical shorting to occur This could severely damage the DH 2 and even cause danger to life AL WAYS allow time for the DH 2 to naturally reach ambient temperatures before connecting the mains power Mounting T
19. e is removed And if you adjust the threshold so that noise can only come through when the signal is loud enough to mask it you lose the ability to include quiet passages in your recordings Commercial noise reduction units now feature a combination of dynamic filtering expansion and even compression and excitation effects which have been included in an attempt to obscure some of the undesirable side effects of the noise reduction processes But these are only partially successful and you still can t master full bandwidth CDs or film soundtracks with them The results simply aren t good enough Whenever a single band expander encounters a signal with amplitude below its threshold it further reduces the volume But what if there is still a significant signal at DH 2 Rev 01 Ver 1 00 Page 5 November 30 2005 say 3kHz but very little elsewhere in the frequency spectrum The single band expander has no way of discerning the genuine signal and shuts this out at the same time as all other frequencies A multi band device separates the audio spectrum into a number of bands and treats each of these as an individual signal This form of noise reduction has evolved from simple analogue units onto Digital Audio Workstations which can incorporate high power DSPs capable of splitting the audio spectrum into multiple bands and applying expansion to each of these in the digital domain But multi band units are still unable to distinguish accurately
20. e processes and create unmusical side effects In addition De Hissing at this stage will make it almost impossible to identify and remove clicks and scratches at a later time De Crackling should be the next process because even small crackles can cause the same problems as in ii above Azimuth Correction can be carried out either before or after De Hissing but experience shows that best results are obtained using the AZ 1 or Phase EX module before De Hiss Finally apply the DH 2 If you have the full range of CEDAR restoration modules they should be connected as shown in the diagram overleaf Please note that to maintain the maximum fidelity and remove and possible sources of degradation between processes connections between modules should be by AES EBU 24 bit format DH 2 Rev 01 1 00 Page 15 November 30 2005 Digitale 44TH Power 10 0dB 40 aeu puse Bypass amp 8 8 3 rose Pre Post Enter n D 6 A CEDAR pecicier pc 1 vede e pem ca Phones Input Level Output Attenuation Contrast SERIES 2 Firstly De Click your material Over en Power cte Bypass Page By w E C Ru Level Post Pre Post Enter ENT A 5 CEDAR CR 1
21. e which enables the System to check the operation of each of its major sub systems plus all of the user controls To enter the self test mode Switch on the DH 2 while holding down the ENTER key The DH 2 will perform each test in turn and you may move to the next test by pressing the ENTER key Consequently any test may be skipped by pressing the ENTER key Note Whilst the SELF TEST is in progress the ENTER key will not initiate a MIDI DUMP ROUTINE 1 BUTTON TESTING ROUTINE The DH 2 will invite you to press each of the Function Keys except ENTER and each of the Dedicated Function Keys Pressing a key will cause the display to change from OFF to ON ROUTINE 2 ATTENUATION KNOB TEST The DH 2 will invite you to turn the Attenuation knob to check that the value displayed on screen matches the position of the knob ROUTINE 3 dial SPIN WHEEL TEST Rotate the dial to check that values change smoothly in both positive clockwise and negative anti clockwise directions ROUTINE 4 LED TEST The DH 2 will flash all six green LEDs ROUTINE 5 METER TEST The DH 2 will invite you to turn the dial to vary the levels displayed by each of the four input and output meters in turn Press ENTER to step to the next meter DH 2 Rev 01 Ver 1 00 Page 43 November 30 2005 ROUTINE 6 DSP1 TEST The DH 2 will test its DSPs and internal memory Please wait for this test to complete If the System is fully functional the scre
22. ed see below The MIDI DUMP will be initiated every time that the ENTER key is pressed regardless of context Input Level This control acts upon the analogue inputs only Use it to adjust the volume of incoming signals to the desired level We recommend a peak level of approximately 0 to 3dB as shown on the Input Signal Meters DH 2 Rev 01 Ver 1 00 Page 21 November 30 2005 Output Attenuation Avoid clipping using the Output Attenuation Control This is not a compressor or limiter and acts purely as a digital gain control with variable gain from OdB to 10dB in 1dB steps DH 2 Rev 01 Ver 1 00 Page 22 November 30 2005 OPERATING THE CEDAR DH 2 2 PAGES The DH 2 has three pages which control all aspects of its operation Each page is selected by pressing the dedicated PAGE function key displayed on the LCD screen and may be controlled using the Function Keys and the a dial Note There is a fourth normally hidden page called the Status Page This is not accessed using the standard Page function and will be discussed separately in the section describing Error Levels PAGE 1 CONTROL PAGE If necessary access this page by pressing the Dedicated Function Key PAGE until the Control Page appears There are five controls in the Control page These correspond to the five soft keys and are to be found directly above each of them as follows F1 Stereo Ganging Left Right Control F2 LEVEL Control F3 A
23. ed in professional audio equipment Connect the output from your source to the balanced analogue inputs of the DH 2 using standard XLR plugs You will require two such connections one for each channel The balanced audio output may be used to connect the DH 2 directly to audio equipment such as mixing desks and professional recorders featuring balanced XLR inputs and outputs ii _ Digital SPDIF format audio data The SPDIF format is used by domestic and semi professional digital audio devices such as DAT machines some ADCs and some CD players Both audio channels are carried along a single cable so you may connect the SPDIF output from your source to the SPDIF input of the DH 2 using a single cable terminated with RCA or plugs The SPDIF output of the DH 2 may be connected to the SPDIF input of your recording device or external DAC iii Digital AES EBU format audio data The digital AES EBU format is used by professional digital audio devices including mastering systems DASH recorders and high quality ADCs amp DACs Both channels of audio are carried along a single cable so you may connect the AES EBU output from your source to the AES EBU input of the DH 2 using a single cable terminated with XLR plugs The AES EBU output of the DH 2 may be connected to the AES EBU input of your digital mixer recording device or external DAC 24 bit Digital data resolution The DH 2 features 24 bit input and output resolution wh
24. educe the noise added in the signal path or are capable of removing it from the final recording Before proceeding any further perhaps it would be best to describe what we mean by the term broadband noise defining it to be a random effect which adds or subtracts a random amplitude at all times to or from all frequencies within the audio spectrum Thus we do not include artefacts of very limited duration such as intermittent electrical clicks or microphone grounding which may be corrected by quite different methods to those described below Next let s dispel any illusions regarding Dolby dbx and similar noise reduction systems These are dual ended processes designed to minimise the accumulation of any extra noise added by the limitations of analogue recording tape Dual ended processes are commonly called encode decode systems because the recording process encodes and the playback process decodes the signal None of these processes enable you to remove noise from within a signal that already contains it they simply stop you adding too much more when you commit that signal to tape and then play it back again Perversely they therefore help your tape deck to accurately record and then faithfully reproduce any noise contained in the original signal So what you need is a single ended process that removes noise from your signals prior to committing them to tape or at the very least improves the signal to noise S N ratio wi
25. efresh Left LEVEL x 100 Left LEVEL x 100 Right LEVEL x 100 Right LEVEL x 100 Left ATTEN x 100 Left ATTEN x 100 Right ATTEN x 100 Right ATTEN x 100 Left BRT x 100 Left BRT x 100 Right BRT x 100 Right BRT x 100 Page 41 2 MIDI The DH 2 is permanently set to transmit any change of control page parameters or Pre Post state via MIDI except when such a change is initiated by an RS232 or MIDI command Therefore if a MIDI sequencer such as Cubase Notator or EditTrack is connected to the DH 2 it will receive a running history of the unit s operation If your sequencer and audio sources are able to send and receive timecode then the DH 2 s MIDI capability may be used as the basis for an automation system Note The absolute parameter values are not transmitted or received so the user must ensure that any changes are relative to a desired starting value which can be set using MIDI DUMP If a MIDI DUMP of all control page parameters and the Pre Post state is required pressing ENTER at any time will initiate the DUMP Additional MIDI Command The DH 2 will receive LOCAL ON and LOCAL OFF commands The Status Page will notify you of the current state Both WARMSTART and COLDSTART always set LOCAL ON This command cannot be initiated from the front panel of the DH 2 DH 2 Rev 01 Ver 1 00 Page 42 November 30 2005 SELF TEST MODE The DH 2 features a powerful self test mod
26. en will display the message Memory passed If a memory error is detected the screen will display the message Memory error at If a DSP failure is detected the screen will display the message DSP1 is not responding If you observe this message please repeat the self test If the message recurs please contact your dealer for assistance WARNING The DH 2 contains no user serviceable parts DO NOT UNDER ANY CIRCUMSTANCES attempt to service your unit ROUTINE 7 DSP2 TEST As above TEST COMPETED Your DH 2 will now prompt you to press ENTER one more time to return you to operating mode whether all tests have been passed or not Some failures will not stop you from using the DH 2 successfully However consistent failures should be notified to your dealer or directly to CEDAR Audio Ltd A FINAL NOTE Some users use commercial test CDs or signal generators to test the operation of components within their audio systems The DH 2 will generate distortion if a digital FSD full scale deflection sine wave is applied to either the AES EBU or SPDIF inputs This does not imply that your DH 2 is faulty and the effect should be ignored DH 2 Rev 01 Ver 1 00 Page 44 November 30 2005 3 16 bit 28 24 bit 3 12 28 32kHz 3 30 32kHz 29 44 1kHz 30 44 1kHz 3 29 30 48kHz 3 30 48kHz 29 30 50 15 34 A to D frequency 20 ADC 3 AES Sync 30 AES EBU 28 AES EBU 11 12 19 28 30 31
27. enever the AES EBU digital input and output are utilised Dithering The DH 2 also features TPDF Triangular Probability Density Function dithering This is applied to the digital data when the SPDIF output format is selected Dithering is always applied to the data presented to the DACs Note In order to fully comply with EMC regulations this unit should be connected via its AES EBU and or analogue connectors Metal shelled XLR connectors should be used We recommend using a good quality starquad cable with three cores connected to pins 1 2 amp 3 The shield of the cable should be connected at both ends to the outer shell of the connector DH 2 Rev 01 Ver 1 00 Page 12 November 30 2005 4 OTHER CONNECTIONS i SMPTE EBU The DH 2 has been designed to host an optional SMPTE EBU interface offering LTC and VITC protocols The standard DH 2 does not support timecode and these connectors are not present ii MIDI INJOUT THRU The operation of the DH 2 may be controlled using the Musical Instrument Digital Interface MIDI Refer to the chapter on Remote Control Protocols for further instructions iii RS232 The DH 2 may be controlled using the standard RS232 serial communications protocol Refer to the chapter on Remote Control Protocols for further instructions DH 2 Rev 01 Ver 1 00 Page 13 November 30 2005 SAMPLE INSTALLATION IDEAS analogue or analogue or analogue or line out digital in digital out dig
28. er form a signed integer 1 Toggle between Pages Command Numbers Command Values OxF7 Clear Errors command value Clear all error messages OxF8 Select Page command 1 Control Page 6 O Control Page 7 Status Page 15 Remote Control Page Any other value Refresh OxF9 Pre Post command 0 Pre 1 Post 1 Toggle Any other value Refresh OxFA Bypass command 0 Bypass OFF 1 Bypass ON 2 RESERVED VALUE 3 RESERVED VALUE 1 Toggle Any other value Refresh O0xCO Digital Output Format 0x80 SPDIF 0x00 AES EBU 1 Toggle Any other value Refresh DH 2 Rev 01 1 00 Page 40 November 30 2005 OxC1 0 2 OxC3 0x20 0x30 0x21 0x31 0x22 0x32 0x23 0x33 0x24 0x34 0x25 0x35 Input Source A to D Frequency Receiver Error Level Set Left LEVEL Alter Left LEVEL Set Right LEVEL Alter Right LEVEL Set Left ATTEN Alter Left ATTEN Set Right ATTEN Alter Right ATTEN Set Left BRT Alter Left BRT Set Right BRT Alter Right BRT DH 2 Rev 01 Ver 1 00 November 30 2005 Any other value Any other value Any other value Any value Any value Any value Any value Any value Any value Any value Any value Any value Any value Any value Any value Analogue SPDIF AES EBU Toggle Refresh 44 1kHz 48kHz SPDIF Sync AES EBU Sync Toggle Refresh 1 Lock 2 Code 3 Trans 4 Valid Toggle R
29. h of them a number of times However in this tutorial we will adjust BRT next followed by ATTEN DH 2 Rev 01 Ver 1 00 Page 36 November 30 2005 Note If you want a particularly clean signal or are processing material with grungy hiss you will need to set the Brightness to a low value Similarly if you want a to achieve an acceptable result quickly use a low Brightness If your defining criterion is signal quality a middle Brightness together with a moderate attenuation will usually offer best results If you want a very clean signal and are prepared to accept the risk of low level artefacts you will obtain the best results using a high value for Brightness You may wish to adjust the LEVEL while you are determining the most suitable setting for BRT Where possible listen to the fidelity of any background instruments and bear in mind the general feeling of air or presence in the signal as well as the quality of any residual noise In general the DH 2 is less sensitive to the Threshold setting when the value of Brightness is low than it is when the Brightness is high You can now adjust the ATTEN control to determine the amount of noise removed Increase ATTEN from 40 0 to 0 0 at which point you will hear that the processed signal is identical to the unprocessed This is because the ATTEN control is limiting the amount of noise removal to 0 at every frequency i e there is no effect You may now reduce A
30. hased and fitted inside your DH 2 Please contact your dealer for details of this DH 2 Rev 01 Ver 1 00 Page 32 November 30 2005 4 STATUS PAGE Access the STATUS PAGE by holding down Function Key F5 and then pressing the Dedicated Function Key PAGE Should the DH 2 fail to function or appear to function incorrectly there may be an error contained within the digital audio data received at the System s inputs The Receiver Error Level see above will notify you when an error has occurred but it will not tell you what it is For many users this information will be adequate but the DH 2 is capable of reporting errors and other status information in more detail The STATUS PAGE will give you information regarding the current status of the DH 2 and will give you details regarding any errors which have occurred since the unit was switched on Three items of information will always be reported by the DH 2 These are DSP1 Status Crashed Timed Out Running DSP2 Status Crashed Timed Out Running Condition Error Emphasis Sample Rate If a remote control error is detected a fourth field will appear Comms Error Illegal Checkbyte Illegal Command Size STATUS INDICATORS The front panel LEDs will help to identify the possible cause if the unit fails to function The following table lists all possible combinations of LED error indications LED flashing Condition Digital The digital input v
31. he DH 2 should be carefully mounted in a 19 EIA rack or placed on a flat stable surface If it is used on a cart or free stand care should be taken when itis moved uneven surfaces or excessive force may cause cart and DH 2 to overturn Do not position the DH 2 in a place subject to strong sunlight excessive dust mechanical vibration or periodic shocks Wall or Ceiling Mounting The DH 2 has not been designed for mounting directly to walls or ceilings Ventilation Good air circulation is essential to prevent internal heat build up within the DH 2 The DH 2 should be situated so that its position does not interfere with proper ventilation The DH 2 should not be placed in any situation which impedes the flow of air through the vents at the front and rear Do not place the DH 2 on a soft surface External Heat Sources The DH 2 should be installed away from significant heat sources such as radiators and if possible away from other audio devices such as amplifiers that produce large amounts of heat Installation in racks with devices such as signal processors or tape machines should not be a problem Power Sources The DH 2 features an auto switching power supply which will work safely on any mains supply in the ranges 95v 130v and 190v 260v 50Hz or 60Hz AC only You should never attempt to modify or adjust the internal power supply in any way It contains no user serviceable parts DH 2 Rev 01 Ver 1 00 Page 8 November 30 2005
32. igital audio signal will be coded as INVALID by the DH 2 Many manufacturers devices do not recognise or act upon this code but those that do may refuse to accept or record the audio DH 2 Rev 01 Ver 1 00 Page 31 November 30 2005 3 REMOTE CONTROL Access this page by repeatedly pressing the Dedicated Function Key PAGE until the REMOTE CONTROL PAGE appears The DH 2 features intelligent auto detection software which monitors the RS232 MIDI and SMPTE EBU if fitted inputs and responds to data received on each and any of them This eliminates the need for a control to select the remote control to be used It is only necessary therefore to select the Channel on which the DH 2 receives commands over MIDI MIDI CEDAR Audio Ltd does not produce software for remote devices to control the DH 2 over MIDI MIDI CHANNEL Ensure that button A is highlighted by a box It is then possible to change the MIDI Channel turn the dial clockwise to increase or anti clockwise to decrease the MIDI Channel To toggle this function on off press the Function Key marked On Coldstart the MIDI Channel defaults to 1 RS232 CEDAR Audio Ltd does not produce software for remote devices to control the DH 2 over RS232 However for users wishing to implement their own control software the RS232 Protocol is outlined in the chapter RS232 Protocol SMPTE EBU Timecode A separate SMPTE EBU reader generator board may be purc
33. increase the value First you will notice that very little happens At these levels you will be in a region in which instruments sound generally uncompressed although there may be noise artefacts present and the high frequency content may occasionally sound gated You might also notice the side effect known as twittering At some point as you continue to increase LEVEL the amount of hiss will begin to decrease rapidly The point at which this occurs is defined by the nature of the noise contained within the signal With further increases the twittering will disappear but you will then cause the on set of high frequency compression gating and the side effect sometimes called glugging The optimum value of value of LEVEL is around the crossover point between the twitters and the glugging Unfortunately if the hiss is highly inconsistent there may be an overlap between the twitter and the glugging regions and no setting that can be considered optimum Note If you are using the analogue inputs you must not adjust the front panel INPUT LEVEL CONTROL after you have found a suitable LEVEL Such adjustment will of course alter the amount of noise being presented to the DH 2 s processors and make the initial LEVEL inaccurate Some users prefer to adjust BRT next whilst others adjust ATTEN Ultimately you will discover that the three main controls are closely related and that for best results you will need to adjust eac
34. iolates the Receiver Error Level or no digital sync is present if requested in I O page 44 1 and 48kHz Unknown sample rate received at inputs Bypass Pre Post One or both of the DSPs have crashed DH 2 Rev 01 Ver 1 00 Page 33 November 30 2005 STATUS PAGE DEFINITIONS Crashed Timed Out Running Error Emphasis Sample Rate Illegal Checkbyte DH 2 Rev 01 1 00 November 30 2005 The DH 2 DSPs are failing to function The only recourse is to switch the unit off wait for a few seconds and then switch on again If this error re occurs please refer your DH 2 to an authorised service centre If for any reason the DH 2 drops out of real time fails to pass audio to the output this error will be reported This should only occur if a sample rate of greater than 50kHz is presented to one of the digital inputs This error is non fatal and the DH 2 should continue to function normally after it has occurred The DH 2 DSPs are functioning correctly and moreover have been doing so since the unit was switched on If the DIGITAL LED is flashing the most serious error will be detailed at this point Errors are fully detailed in the DH 2 Service Manual If no error is detected the I O status will display the Emphasis condition OFF The Emphasis bit is not set The DAC de emphasis will not be engaged 50 15 The Emphasis bit is set to 50 15 5 The DAC de emphasis will be engaged J17 AES EBU on
35. is small 6dB or less the Threshold can be set lower and the Brightness can be set higher without introducing twitters or hiss modulation DH 2 Rev 01 Ver 1 00 Page 38 November 30 2005 THE TUTORIAL We have supplied you with a DAT containing three samples of hissy music These samples may prove useful in helping you to learn the features and capabilities of your DH 2 TRACK 1 SEGOVIA Solo guitar is often difficult to restore but this track is of generally good quality and does not have a particularly high level of hiss It is therefore fairly simple to process and achieve excellent results LEVEL does not need to be set very high although high enough to avoid twittering and this minimises the danger of unwanted side effects ATTEN should be set more carefully because an acoustic guitar offers a rich harmonic content that could be damaged by over processing You will find that BRT can be set close to its theoretical optimum Light processing LEVEL 29 4 19 8 ATTEN 4 3 BRT 50 3 50 3 Heavier processing LEVEL 29 4 19 8 ATTEN 6 5 BRT 30 2 302 Note This is a stereo track so values are shown as Left Right pairs TRACK 2 LOUIS ARMSTRONG AND THE HOT FIVE This track is taken from a 78rpm record and is therefore of lower quality with limited frequency response and a higher level of hiss It is therefore more difficult to process than track 1 Firstly LEVEL must be set much higher than before otherwise the
36. ital in TURNTABLE OR RECORDER TAPE MACHINE 1 DH 2 used in line for transcription or broadcast purposes analogue analogue or analogue or line out digital in digital out digital in effects return 2 DH 2 used on the effects loop within a studio environment analogue or analogue or analogue or analogue or analogue or line out digital in digital out digital in digital out digital in CEDAR m RECORDER or other workstation editor 9 DH 2 used in line prior to an editor or audio workstation DH 2 Rev 01 Ver 1 00 Page 14 November 30 2005 A GUIDE TO RESTORATION PROCESSING Contrary to common sense the order in which restoration processes are carried out makes a great deal of difference to the quality of the final result Consequently there is one right way and many wrong ways to restore your material Following these guidelines will help you to achieve the best results on most material Note De Clicking De Scratching should ALWAYS be carried out first This is because i Large clicks make it difficult for the De Crackling process to identify and remove the tiny clicks and crackles that constitute surface noise buzz and other such problems ii All clicks and scratches are in effect tightly defined packets of white noise If clicks are presented to any of the CEDAR De Hiss products HISS 1 HISS 2 Auto De Hiss Dehiss Dehiss2 the DH 1 or the DH 2 they confuse th
37. level The error levels are Note 1 Lock This is the weakest detector and will only cause the LED to flash when the DH 2 believes that there is no usable signal being presented to the selected digital input 2 Code If there is an incoming signal yet the LED flashes on error level 2 the DH 2 is indicating that the signal contains coding violations In some cases you may obtain usable audio However this warning may be caused by non AES EBU or non SPDIF data being presented In these cases any audio produced will almost certainly be unusable 3 Trans This indicates that the incoming digital audio data is of poor quality i e very noisy or jittery and that undetectable data errors are likely These errors will not be corrected by any standard AES EBU or SPDIF device and may lead to audio degradations 4 Valid This is the most stringent test of the incoming data and will cause the LED to flash if the DH 2 determines that any of the data contained in the signal is not valid This is often non fatal i e you will hear perfectly good audio but it indicates that some device or anomaly in your audio chain is generating digital audio data outside of the AES EBU or SPDIF specifications published by their respective bodies Please note however that if the digital LED does not flash this can not be taken as an absolute statement that the signal conforms to specification If the error level selected detects an error the d
38. ly The Emphasis bit is set to CCITT J17 The DAC de emphasis will not be engaged Unknown AES EBU only The Emphasis status is not indicated The DAC emphasis status will not be altered If no digital data error is detected the measured sample rate presented to the digital inputs will be displayed to the nearest 100Hz The RS232 or MIDI has received a command packet containing an illegal checkbyte byte2 Page 34 Illegal Command Type The RS232 or MIDI has received a command packet containing an illegal command type byte4 DH 2 Rev 01 Ver 1 00 Page 35 November 30 2005 TUTORIAL One method for determining the correct values of the DH 2 noise removal controls is outlined below It is important that the audio presented to the DH 2 is free of clicks and crackle This is because these degradations will interfere with the de hissing process and prevent you from reaching an optimal result Please note that the tutorial assumes that the material is stereo and exhibits virtually identical noise characteristics in each channel 1 2 Ensure that DH 2 is in POST and that BYPASS is OFF Select the Control Page and press CLEAR to reset the values of the DH 2 s process controls to their defaults Your first task will be to find the most appropriate setting for the LEVEL control This will be the single biggest influence on the quality of the processed signal Starting with LEVEL at 0 00 use the dial to
39. may be adjusted as follows Press F2 to select the LEVEL control A box will appear around the numerical display to indicate that the control is selected Rotate the dial clockwise and or anti clockwise to alter LEVEL in steps of 0 01 Rotating the dial slowly will result in delicate adjustments whilst faster rotation will increase the rate at which LEVEL changes ATTEN ATTEN sets a maximum limit on the amount of noise that the DH 2 will remove at any time at any given frequency It is quantified in dBs The side effects introduced by inappropriate use of LEVEL are exaggerated when the DH 2 is asked to remove too much noise Correct use of ATTEN will ensure that none of the side effects caused by over or under processing are heard in the output signal In cases of difficulty you can often trade off the side effects against the amount of hiss reduction ATTEN may be adjusted as follows Press F3 to select the ATTEN control A box will appear around the numerical display to indicate that the control is selected e Rotate the dial clockwise and or anti clockwise to alter ATTEN in steps of 0 1 Rotating the dial slowly will result in delicate adjustments whilst faster rotation will increase the rate at which ATTEN changes DH 2 Rev 01 Ver 1 00 Page 25 November 30 2005 BRT Brightness controls how the DH 2 compromises between the various side effects Its theoretical optimum is 50 However in practice
40. me manner will only remove 8 units of the 20 On the other hand a subtractive filter which is practical only in the digital domain will still remove the full 20 units equivalent to a filter reduction of 50 This is of course what we want because the noise at this moment represents 50 of the total signal amplitude So now we arrive at the most sophisticated noise removal technology yet implemented in a commercial sense computerised spectral subtraction The concept of Spectral Subtraction becomes useful when a DSP is used to split an audio signal into hundreds of bands You can then be very precise about how much noise you remove subtracting a lot at say 8kHz while leaving 8 1kHz virtually untouched But if this sounds to good to be true it is The noise spectrum the sonic fingerprint can only be accurately measured if there is an otherwise silent passage within the music If the fingerprint is not accurate the amounts subtracted will be wrong leading to unpleasant side effects And worse still many tracks are close edited making it impossible to obtain any such fingerprint But let s assume that you have obtained a perfect fingerprint You might expect to produce a good restoration with large amounts of noise removed and few or no side effects Yet experience shows that all attempts to implement spectral subtraction in this unmodified form produce both i unacceptable artefacts and ii unusably dry and dull results This is in
41. nalogue Then press PAGE twice more to return to the Control Page If you are using digital inputs from a consumer format machine such as a domestic DAT recorder press PAGE once then press B twice to select SPDIF If you are outputting to a consumer format machine such as a low cost DAT recorder press A function key F1 to select SPDIF format Press PAGE twice to return to the Control Page Note The DH 2 defaults to AES EBU PROFESSIONAL format so skip both instructions 5 i and 5 ii if your DH 2 is connected via its AES EBU input and output Play your material through the DH 2 Press function key F2 to select the LEVEL control and use the a dial to vary LEVEL between 0 00 and 99 00 Provided that the material you are playing contains hiss you will at some point within the scale hear it disappear With ATTEN set to 40 0 and BRT set to 0 00 you will almost certainly hear side effects while you adjust LEVEL Experiment with ATTEN and BRT to hear how these affect the output Please refer to the TUTORIAL section for a full explanation of these controls how they interact and how to get the best results from them This section should have whetted your appetite so you should now proceed to the rest of the manual DH 2 Rev 01 Ver 1 00 Page 19 November 30 2005 WARMSTART AND COLDSTART The DH 2 features Warmstart and Coldstart options Warmstart has been added so that the unit can be configured once and these parameters a
42. ncoming analogue signals to the desired level A level of approximately O to 3dB as shown on the Input Signal Meters will offer best results The Input Level Control may be physically bypassed internally to obtain the best possible signal to noise ratio S N from the ADCs This work must be carried out by qualified service personnel so please refer to your authorised dealer or directly to CEDAR Audio to have this modification performed Output Attenuation Control A digital gain control with range 0 to 10dB in 1dB steps Function Keys Use along with the LCD screen Please refer to the following chapters for full instructions Contrast Control The LCD screen may be adjusted for optimum visibility Use a fine screwdriver to make such adjustments DH 2 Rev 01 Ver 1 00 Page 18 November 30 2005 QUICK TOUR If you are impatient to hear some immediate results using your DH 2 the following instructions should have you up and running within a few minutes T 2 5 i 5 ii READ THE SAFETY INSTRUCTIONS Connect the DH 2 to the mains supply Connect your input and output devices to the DH 2 using the appropriate input and output sockets If in doubt please refer to the section CONNECTING THE DH 2 and the manuals of your other equipment Referring to the front panel diagram hold down the function key F1 and switch on the DH 2 If you are using analogue inputs press PAGE once Press B function key F2 to select a
43. nd the packaging the carton should contain the following mains connection lead e this manual blanking plates which may be used to replace the rack mount ears DH 2 Tutorial DAT 2 INSTALLATION SITE The DH 2 may be used in most areas but to maintain reliability and prolong operating life observe the following environmental considerations Nominal temperature should be maintained between 5 and 35 Centigrade 41 and 95 Fahrenheit e Relative humidity should be in the range 30 to 60 non condensing Strong magnetic fields should not exist nearby 3 RACK MOUNTING The DH 2 can be mounted in a standard 19 EIA rack 4 FREE STANDING USE The DH 2 can be used as a free standing unit The rack mount ears may then be replaced by the blanking plates if desired To replace the ears with the blanking plates Unscrew the three bolts which attach each ear to the chassis of the DH 2 Attach the blanking plates using the same retaining bolts Do not over tighten these bolts as doing so may cause damage to the DH 2 DH 2 Rev 01 1 00 Page 10 November 30 2005 CONNECTIONS The DH 2 may be connected to most of the professional audio equipment currently available Three types of audio input and output are provided one analogue and two digital and these will satisfy most users interconnection requirements Full descriptions of these connectors will be found later in the manual 1 BEFORE CONNECTION To prevent problem
44. ng the DH 2 you should always allow a few seconds between switching the unit off and switching it on again DH 2 Rev 01 Ver 1 00 Page 20 November 30 2005 OPERATING THE CEDAR DH 2 1 DEDICATED CONTROLS The DH 2 features a number of dedicated controls to speed operation These are now explained in turn Bypass You may wish to bypass completely the operation of the DH 2 Press BYPASS to do this The current status will be indicated on the Status LED The Bypass does not hard wire the input to the output Analogue signals still pass through the A D and D A stages Notes There is a delay of approximately 1 3mS in any analogue to analogue signal passed through the DH 2 in Bypass mode e There is a delay of approximately 0 1mS in any digital to digital signal passed through the DH 2 in Bypass mode e All delays are group delays i e are constant at all frequencies and are measured at a sample rate of 44 1kHz Page Use this Function Key to move between Pages Pre Post It will often be useful to compare the original signal with the post processing output of the DH 2 The current status will be indicated on the Status LEDs Enter The ENTER Key has three functions as a LOCK OUT key preventing accidental changing of parameters as a CLEAR key resetting error messages and as a MIDI DUMP command These first two functions are of course context sensitive and the key s action will be appropriate to the page display
45. ogue inputs and outputs for connection to professional analogue equipment ADC and DAC converters using the latest 64x over sampling A gt Delta Sigma technology 2103dB dynamic range A D and gt 93dB dynamic range D A Mountable in a 19 EIA rack Remote control via MIDI and RS232 interfaces SMPTE EBU timecode capabilities via optional upgrade Input and output LED bar graph VU meters Twin 40 bit floating point DSP processors delivering 50MFlIops to handle the most complex audio processing requirements High levels of artificial intelligence designed into the DH 2 program algorithms making it extremely simple to use DH 2 Rev 01 Ver 1 00 Page 3 November 30 2005 THE BACKGROUND TO CEDAR NOISE REMOVAL Cheap digital audio i e CD has made discerning listeners quite intolerant of the noises and distortions present in analogue audio signals After all in a perfect digital world there are no clicks crackle pops buzzes or hums and no hiss so it s a shame that we live in a far from perfect world Even today the vast majority of mixing desks still have all analogue signal paths so most DDD classified CDs are still mastered through numerous analogue stages And vintage i e pre 1980s recordings are by definition re mastered from analogue disks and master tapes which inevitably suffer from at least one of the degradations listed above So recording engineers are turning more and more to the technologies that r
46. re then automatically recalled on every power up This is ideal for applications where time consuming set ups at the start of each session are not practical Coldstart If the DH 2 has not been used for some time the system will automatically Coldstart This process initialises all parameters to their factory default values and after a few seconds the DH 2 will automatically enter at Page 1 On start up the message Coldstart will be displayed at the top right of the start up screen on the LCD display The screen will then enter PAGE 1 which will show the default parameters The default values are LEVEL 0 00 ATTEN 40 0 BRT 0 00 Other default values Digital Output AES EBU Input Source AES EBU Receiver Error Level 1 Lock MIDI Channel 1 Bypass OFF A to D frequency 44 1kHz Pre Post Post Warmstart The DH 2 remembers the latest parameters used and the page that was active at the time that the system was last switched off On start up the DH 2 will display the message Warmstart on the screen and after a few seconds will re enter at the appropriate page with all user parameters set to their previous values User Coldstart If you wish to force the DH 2 to Coldstart hold down Function Key F1 while switching on the system Release F1 when the message Coldstart is seen on the LCD display Note In common with all other digital devices and irrespective of whether you are Warmstarting or Coldstarti
47. s and possible equipment damage turn off the power to all equipment before making connections e Be sure to insert plugs firmly into sockets Loose connections may cause hum and noise e When unplugging any lead do so by grasping the plug not the lead 2 POWER CONNECTIONS Ensure that the DH 2 is switched OFF before inserting the mains lead NOTE Users with 2 pin mains supplies When the DH 2 is connected to other audio components the AC hum of the unit may be increased or decreased by reversing the direction of the power connector in the socket Check that the cord is in the favourable position in with respect to other audio devices in the chain This will ensure that the best sound quality is obtained from your DH 2 For further information on grounding and polarity consult a person familiar with studio grounding techniques 3 SIGNAL LEAD CONNECTIONS Refer to the Rear Panel diagram The DH 2 offers three audio connection standards one analogue and two digital These are balanced analogue audio I O digital SPDIF format audio data digital AES EBU format audio data Note that the DH 2 always passes its output to all three signal outputs irrespective of the input used but that the digital data will only be formatted for either AES EBU or SPDIF as defined by the user parameters DH 2 Rev 01 Ver 1 00 Page 11 November 30 2005 i Balanced analogue audio I O Pin 2 This standard is us
48. the optimum setting for Brightness depends upon the nature of the signal and the hiss contained within it It may also be influenced by any compromises you wish to make in order to achieve certain results Brightness too low At lower brightness settings the DH 2 will favour consistent compression instead of more unmusical or artificial sounding artefacts Generally a low brightness is appropriate if you want to remove a lot of noise Brightness too high At higher brightness settings the DH 2 will minimise the compression of any low level signals but becomes susceptible to twitters and noise pumping A high brightness is suitable when you wish to remove a small amount of noise Note You will find that the threshold and the brightness interact Higher brightnesses will require slightly higher thresholds than lower brightnesses BRT may be adjusted as follows Press F4 to select the BRT control A box will appear around the numerical display to indicate that the control is selected Rotate the dial clockwise and or anti clockwise to alter BRT in steps of 0 01 Rotating the dial slowly will result in delicate adjustments whilst faster rotation will increase the rate at which BRT changes Ganging The DH 2 may be used to process stereo material The left and right channels of such material can be entirely independent and exhibit quite different noise characteristics The Ganging control allows you to select which channel s
49. thout affecting the signal adversely Which brings us neatly to the volume control stunningly effective at removing noise it does nothing to improve the S N ratio and has an all too noticeable side effect No noise No signal Since broadband noise is most intrusive at high frequencies where the masking effect of loud sounds is least present the first stage in our evolutionary tale of noise removal is the simple low pass filter Less damaging than the volume control which removes the signal altogether this only removes a proportion of any signal present above its cut off frequency fc Unfortunately if at the given frequency you reduce the amplitude of the noise content of your recording by say 6dB you also reduce the genuine signal at this frequency by the same amount This may be acceptable if the recording has little or no high frequency content but natural sounds and modern electronic instruments have significant components up to and beyond the limits of human hearing Consequently the low pass filter will only be successful in processing your antique collection of 78 s and even then only at a cost But this gives us a hint as to how a more effective single ended noise reduction system could be designed perhaps a device could be built which removes the high frequencies when there is no signal present but leaves them untouched when the noise is being masked by genuine high frequencies It s a Dynamic Filter so called DH 2 Rev
50. ument largely to do with the statistical nature of broadband noise it suggests a device which will eliminate some of the noise a Noise Gate This detects when the signal drops below a certain threshold set by the user and then cuts off the signal entirely There are many enhancements to the Gate idea such as variable attack and release times and hysteresis all added to limit the occurrence of damaging side effects but the principle always remains the same if the total signal drops below the amplitude threshold the gate shuts off the signal Just as the filter can be improved by making it dynamic so can the gate Such a device is called an Expander The Expander still has a threshold control but unlike the gate the Expander applies a progressive gain reduction the amount of which is determined by the settings selected by the user For example if a signal drops 3dB below the threshold the Expander may reduce the signal volume by 6dB 12dB or any other figure depending upon the expansion ratio Unfortunately the subjective difference between the noise gate and the expander is small and though they sound great in theory they don t sound so great in reality Being time domain processes they have advantages and disadvantages when compared to frequency domain filtering but only sound different not better In particular they have the distinct advantage that when active they remove all the noise but once inactive or open no nois
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