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Prism Sound ADA-8XR Operation Manual

1. 28 7 3 1 Truncation and dithering cececcccceceeeeeeeeeee aces aea ea aaaea Ede i dae iranda 28 7 3 2 NolSe Shapinguusuuunsagsenese id rallada 29 7 3 3 Wordlength and the ADA 8XR eerernnrrvnrennrrvnrennrrenrennrrnnsrnnrrersennrressennrressrnnnne 29 7 4 Prism Sound MR X and DRE encoding processes rurrrrrnnnarvrrnnnnrvrrvnnnrrrrnnnrrrrrnnnenr 31 7 4 1 Prism Soina MRX occitano A N G 31 7 4 2 Using Prism Sound MR X with the ADA 8XR essvrnnrensrvnrensrrnnnennrrnnrersrrnnsennnr 32 7 4 3 Prism Sound DRE Dynamic Range Enhancement ococcccccncoccccconancccnanancncnanns 33 7 4 4 Using Prism Sound DRE with the ADA 8XR eeennrrrnnrennrrvnrennrrnnernsrrensensrrensernnr 33 7 5 Prism Sound Overkiller cccecsecceeeeseeeeeeeeeneeeeeeneeeeeeneneeceeeneeeedsneeececseneeeeeneeeeees 34 O Prism Media Products Limited 2001 2004 Page 1 4 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 7 6 Sample rate conversion and Prism Sound SSRC cccececcecceeeceeeeeeeeaeeeeeeeeeeeees 34 EL Reterences nt eee 35 8 SPecifiCatiONS coins a da 36 811 IEN EI a E da n 36 82 SYNCNLOMIZAOM ii E O E GR 36 B23 Mono 37 MS EE A A E E N A AAA 37 ea IEP a ELSE 37 9 GIOSSANY cuasi ini 38 O Prism Media Products Limited 2001 2004 Page 1 5 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 1 Introduction The ADA 8XR is the latest i
2. a family of Prism Sound noise shapers providing optimal A D conversion or wordlength reduction See also An AES3 interface carrying extended sample rate audio by carrying odd and even samples in the A and B channels respectively Thus the interface can carry only one audio channel This technique is also being applied to other interface formats including MADI and ADAT where half the normal channel count is sacrificed Prism Sound Synchronous Sample Rate Conversion a sample rate conversion technique without the distortions associated with conventional asynchronous rate converters A high speed Reference Sync format at 256x the audio sample rate passed directly between equipment on coaxial cable in order to remove the need for each equipment to have its own clock multiplying PLL First used on Digidesign Pro Tools I O interfaces this technique is questionable since it is the PLLs which allow incoming Ref Sync jitter to be eliminated from the point of conversion Jitter from the Superclock cable results directly in sampling jitter and thus in distortion An eight channel digital audio interface format first used in Tascam DA 88 recorders Loss of resolution shortening of wordlength in a digital audio signal path which if not accompanied by dithering or noise shaping results in truncation or quantization distortion products See Split96 A Reference Sync format comprising a TTL square clock at the sample rate tra
3. SNS3 and SNS4 are optimal shaper designs their shaping is quite extreme in order to get the maximum theoretical subjective improvement in noise performance based on an average human low field sensitivity curve This results in the addition of larger amounts of high frequency noise It is difficult to assess the difference in sound between different noise shapers for any given program material since their effects are at very low amplitudes the OdB line on the plots below represents flat dither with an rms noise amplitude of about 93 4dBFS It is tempting to audition noise shapers by using a low signal level and boosting the shaper output by tens Prism Media Products Limited 2001 2004 Page 1 29 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 of dBs in the digital domain prior to monitoring using for example the microscope feature on Prism Sound test equipment Using this method it is easy to hear that the noise floor of more extreme shapers is clearly not white switching say from SNS1 to SNS4 sounds like shhhhh ssssss as the noise is shifted towards the higher frequencies However this is not really a meaningful test since the sensitivity of the ear at different frequencies is very dependent on level and the design of the more extreme shapers is in any case intended to render the noise floor completely inaudible at normal listening levels Ultimately the only right cho
4. LUM UM erter ADA 8XR Multi channel A D D A Conv Operation Manual SAMPLE RATE ko 2 ut ox Select Enter Change Aes Mo SA La gt t Bank CONFIGURATION I STORES 1 2 3 4 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 Operation Manual Revision History Rev Date Author Comments 1 00 4 December 2004 lan Dennis Initial release with 2 00 firmware Support Contacts Prism Media Products Limited Prism Media Products Inc William James House 21 Pine Street Cowley Road Rockaway Cambridge CB4 OWX NJ 07866 UK USA Telephone 44 1223 424988 Telephone 1 973 983 9577 Fax 44 1223 425023 Fax 1 973 983 9588 Email tech support prismsound com Web http www prismsound com Or contact your local Prism Sound distributor as detailed on the website Trademark Acknowledgements Digidesign Pro Tools Pro Tools 24 MIX 888 24 I O Pro Tools HD 192 I O 96 I O SYNC I O and DigiLink are trademarks of Digidesign a division of Avid Technology Inc Direct Stream Digital DSD MAC DSD SuperMAC and the DSD logo are trademarks of Sony Corporation Super Audio CD SACD and the SACD logo are joint trademarks of Sony Corporation and Philips Electronics N V All trademarks acknowledged 2001 2004 Prism Media Products Limited All rights reserved This manual may not be reproduced in whole or part in any medium without the written permission of Prism Media Products Limited
5. 6 and the new extension for 20 bit media is known as MR X gt 0 Note that all of the above Track Modes are identified by the generation of an invisible tag code which allows the decoding device to automatically select the correct Track Mode to decode on playback or reception MR X is also useful for recording or transmission of extended sample rates in conjunction with extended wordlengths by employing Split96 interfacing see section 7 3 along with MR X In this way for example MR X can be used to record stereo 96kHz 24 bit audio on a standard DA 88 tape MR X applies indivisibly to an entire bank of eight channels on the target medium This is because audio extension data and format identification data are passed on the sacrificed channels In the case of the ADA 8XR this means that MR X encoding or decoding must be applied to the entire eight channel Digital Output or Input Modules 7 4 2 Using Prism Sound MR X with the ADA 8XR MR X encoding is selected within the Dither Encode box of the Mimic Panel as described in section 5 1 4 MR X encoding is indicated by the MR X LED being lit if the 20b LED beneath is also lit MR X29 encoding is indicated otherwise MR X46 encoding is indicated When selecting MR X encoding MR X or MR X29 mode must be explicitly selected Beyond this the Track Mode is determined by the output wordlength selected in the same box MR X decoding is selected within the Decode box
6. are used to navigate up and down through the different menus at a CONFIGURATION STORES particular level the Select Change Beis A A ee keys lt and gt are used to select different values for the parameter in the current menu and the Enter Accept key is used to confirm the new setting or to descend to a lower menu level Select Enter i Change Accept Menu 7 lt gt t Note that certain numeric parameters such as analogue line up levels change dynamically with the operation of the lt and keys and do not need to be confirmed with Enter Accept For most operations it is not necessary to navigate to the desired menu using the Menu keys 1 and since the blue Access buttons in the other panels jump immediately to the menu or menus which apply to that area of the front panel Where more than one menu is associated with an Access button repeated pressing of that Access button cycles through them The first press of any Access button jumps immediately to the last menu which was accessed in the associated group so repeated access to a common menu becomes a one button operation The Configuration Stores buttons provide access to a store system of 24 stores arranged as four banks of six stores each All of these stores are user configurable although some of them initially contain factory default stores Detailed description of the operation of the store s
7. In accordance with our policy of continual development features and specifications are subject to change without notice Prism Media Products Limited 2001 2004 Page 1 2 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 WARNING TO PREVENT FIRE OR SHOCK HAZARD DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE DO NOT REMOVE THE COVER NO USER SERICEABLE PARTS INSIDE REFER SERVICING TO QUALIFIED SERVICE PERSONNEL Statements of Conformity This equipment has been tested and found to comply with the limits for a Class B digital device pursuant to Part 15 of the FCC Rules These limits are designed to provide reasonable protection against interference in a residential area This device generates and uses radio frequency energy and if not installed and used in accordance with the instructions may cause interference to radio or TV reception If this unit does cause interference to radio or TV reception please try to correct the interference by one or more of the following measures a Reorient or relocate the receiving antenna b Increase the separation between the equipment and the receiving antenna c Plug the equipment into an outlet on a different circuit from the receiver d If necessary consult your dealer or an experienced radio or TV technician CAUTION Changes or modifications to this equipment not expressly approved by the manufacturer could void the user s authority to operate this e
8. RCA phono adapter included AES11 ref sync I O are on XLRs wordclock ref sync I O are on BNCs serial comms jumpered for RS 232 is on DB9 male Plug in the unit and switch on the power switch which is integral to the power inlet The ADA 8XR should briefly light all LEDs then settle into its default setup with the level screen displayed on the LCD display The unit can thereafter be turned off and on using the Standby key in the top left hand corner of the front panel 2 2 Configuring the ADA 8XR The user interface of the ADA 8XR is a three tier system If your application is fairly standard you will probably be able to load a Factory Store and be up and running straight away There may be a few changes which you need to make to the loaded Store which you can most easily do using the blue Access buttons to take you straight to the Menus you need If your application is unusual in its details you may need to navigate the Menu system manually First have a look at the available standard Factory Stores at the end of the Firmware Reference These apply to most non workstation applications If you re using a dedicated Workstation I O Module look instead at the Factory Stores section for that Module in the I O Module Reference Hopefully one of the Factory Stores will be either exactly what you need or close to it Select the most appropriate Factory Store by pressing the Bank button at the bottom left o
9. be made per channel these buttons take on that function whilst that menu is selected 4 4 Two channel Monitor Apart from its two eight channel Paths the ADA 8XR has a separate two channel Monitor which can be assigned to either Path It has a headphone output as well as analogue and digital line outputs It has the usual Cut Invert Swap and Mono functions along with a volume control which can be switched out if you want to use an external control for the line volume Inserting the headphones can be made to mute the line outputs if required The Monitor can be set to Pairs or Mix mode In Pairs mode it simply monitors adjacent pairs of channels odd to the left even to the right as selected by the Channel Select buttons In Mix mode a mix of any or all of the eight channels in the Path can be built up each with its own gain and pan You can switch between separately adjusted mixes for each Path 4 5 Configuration Stores These buttons are used to change the entire setup of the ADA 8XR between preset configurations for different tasks There are four Banks each containing six entire Stores of the ADA 8XR state thus a total of 24 stores are available Each store can have a name of up to 16 characters to ease identification Pressing either the Bank button or one of the Store number buttons 1 6 attracts the attention of the LCD display to the Configuration Store system The name of th
10. is inserted in the right orientation to match the positioning of the fuse and clip the cover cannot be fully closed O Prism Media Products Limited 2001 2004 Page 1 23 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 6 2 Adding I O Modules WARNING It is NOT necessary to remove the top cover of the ADA 8XR to A add or remove I O Modules Removal of the top cover with the mains supply connected presents a risk of electric shock NOTE Inserting or removing I O Modules should be carried out with the power disconnected from the ADA 8XR Failure to do this may result in damage to the ADA 8XR the I O Module or both NOTE To protect from static damage I O Modules are supplied in anti static packaging When removed from this packaging I O Modules should be handled only by their metal end plates The packaging should be retained and Modules removed from the frame should be stored in it To decide on the location of a new l O Module refer to the diagram of the ADA 8XR rear panel in section 3 2 When viewed from the rear the analogue I O AIO slots are the larger castellated panels on the left AIO1 above AlO2 below and the digital I O DIO slots are the smaller castellated panels on the right DIO1 above DIO2 below In general the ADA 8XR software regards the analogue slots as interchangeable and likewise the digital slots When loading stored configurations slot assignments are adjusted t
11. of rates at which the oscillator needs to operate to small islands around the standard sample rates we could use a bank of oscillators selecting the appropriate oscillator according to our desired sample rate But this is expensive and in any case the pull range of an ordinary quartz crystal oscillator is still generally insufficient to meet the tolerance demands of the digital audio interfacing standards As well as a very stable clock oscillator a good sounding converter must have a PLL phase locked loop with a loop filter which steeply attenuates incoming reference jitter towards higher frequencies Unfortunately even if sourcing equipment provides a carrier with low jitter cabling always adds unacceptable amounts especially poor quality or high capacitance cable which results directly in sampling jitter in the receiving converter if filtering is inadequate But why are these things so important 7 1 3 Analysis of sampling jitter Analysis of sampling jitter small variations in the sampling intervals of an A D or D A converter shows that it produces a similar effect to phase modulation where distortion components appear as sidebands spaced away from the frequency of a converted tone by Prism Media Products Limited 2001 2004 Page 1 25 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 the frequency of the jitter itself These components get louder as the amount of jitter increases b
12. other for instance The Monitor and Meters can be positioned Pre or Post the Path s Processing function if any but in systems without the Processing suite installed or with it turned off these buttons don t change anything 4 2 Menus or dedicated controls The ADA 8XR has a novel operating philosophy We were concerned that the unit should be simple to use even though its flexibility and modularity mean that it has very many controls and will have even more in the future We know that nobody likes menus it takes a long time to find what you need On the other hand a button and a display for everything wouldn t fit on the front panel and would be confusing and we couldn t add new features in later software releases So the ADA 8XR control surface is based on four panels from left to right the Monitor Mimic Meter and Menu panels all alliteration absolutely accidental 4 3 Monitor Mimic Meter and Menu Panels In the Menu panel you will find a huge menu details of which are included in the accompanying Firmware Reference and the Configuration Store buttons It is possible to do nearly anything through the menu system but you have to know where to look This is where the other panels come in The Mimic panel shows a diagram of a Path through the ADA 8XR each Path is actually eight audio channels in parallel so the Mimic panel actually only shows one eighth of a Path The A D Path for example usua
13. registers or by an even more effective technique called noise shaping Noise shaping is just like conventional dithering except that the error signal generated when the unwanted low order bits are discarded is filtered and subtracted from the input signal You can t get something for nothing the error cannot be simply cancelled out because we already know that the output hasn t got enough bits to precisely represent the input But by choosing an appropriate shape for the error filter we can force the dither noise error signal to adopt the desired shape in the frequency domain we usually choose a shape which tracks the low field perception threshold of the human ear against frequency As can be seen from the plots below this has the effect of actually lowering the noise floor in the more sensitive frequency bands when compared to the flat dither case The theory of noise shaping has been around for a long time certainly since well before DSP in real time was feasible for audio signals It has applications in many signal processing and data conversion applications outside audio It has been well researched and is not in the least bit mysterious Proprietary wordlength reduction algorithms are generally conventional noise shapers Assuming that the basic implementation and dither levels are correct the only significant freedoms available to the designer are to choose the actual shape of the noise floor and to decide how
14. side of the rear panel of the ADA 8XR when viewed from the back WCK wordclock is a TTL level square wave with its rising edge indicating the reference s sample instant this is connected to the BNC ref sync input of the Utility Module AES is an AES11 DARS or AES3 format reference signal connected to the XLR ref sync input of the Utility Module or an AES3 id format reference signal connected to the BNC ref sync input of the Utility Module Video is an analogue video signal PAL SECAM or NTSC applied to the BNC ref sync input of the Utility Module DI1 and DI are ref sync inputs from the Digital I O Module fitted in the upper or lower DIO slot respectively Refer to the Module Reference for more information about the Utility Module and its connections The six LEDs on the right hand side of the box indicate the Path s sample rate The combination of the 32k 44k1 and 48k LEDs along with the multiplier LEDs for x2 and x4 allow for display of standard audio sample rates between 32kHz and 192kHz Note that availability of rates may depend of which I O Modules and firmware version are installed in your unit See the Module Reference for details of the capabilities of current I O Modules The Ext LED is lit whenever the Path s nominal sample rate has been set to follow that of the selected external sync source It is important to note that the ADA 8XR does not insist o
15. to adapt this if at all to different sample rates 7 3 3 Wordlength and the ADA 8XR The ADA 8XR provides a comprehensive choice of processes to optimally generate a reduced output wordlength from an analogue or digital source It also includes encoding processes which allow extended wordlengths to be recorded on or transmitted via shorter wordlength equipment as described in section 7 4 These comprise flat dithering plus a selection of four Prism Sound SNS Super Noise Shaping algorithms The four SNS algorithms are designated SNS1 to SNS4 in increasing order of the degree of shaping The spectra of the four SNS algorithms are shown below Note that unlike some noise shaping algorithms SNS spectra are adjusted automatically to provide optimum subjective advantage at each different sample rate and wordlength The spectra are shown below for 16 bit output at 44 1kHz 48kHz and 96kHz sample rates only SNS1 provides only a very small subjective noise advantage but only applies limited noise lift at quite high frequencies In many applications particularly those where the program material is already quite noisy this type of shaper is very often preferred SNS2 is a happy medium It provides a good amount of subjective lowering of the noise floor but with addition of only moderate amounts of high frequency noise It also has the advantage that the noise floor remains subjectively white even when artificially amplified
16. wire or two wire format Since all input and output ports can be individually defined it can be used in mixed format environments or to convert either format to the other The ADA 8XR does not support four wire interfacing 7 3 Wordlength dithering and Prism Sound SNS Super Noise Shaping 7 3 1 Truncation and dithering There are many points in a digital audio signal path where precision can be lost For example in a digital transfer from 24 bits to 16 bits or in an analogue to digital conversion In this situation it is not sufficient just to discard low order bits this causes truncation distortion characterised by aharmonic frequency components and unnatural harsh decays Instead it is preferable to use some sort of dithering process whereby the truncation process is linearized by modulating the signal prior to the truncation usually by the addition of a small amount of noise By adding a random element to the truncation decision small components as far as 30dB below the noise floor can be accurately represented and an analogue like low signal performance can be realised This is achieved at the expense of slightly raising of the noise floor although with some dithering schemes such as noise shaping linearization can be achieved with no noticeable increase in noise How can dithering allow information to be preserved below the least significant bit It seems impossible Consider a simple example where the a
17. 24 bits at these rates It is uncommon to find 4x recorders or channels which do not support full 24 bit operation 7 4 Prism Sound MR X and DRE encoding processes Section 7 3 was concerned with limitations in signal quality imposed by restricted audio wordlengths and described the dithering and noise shaping processes used at points of wordlength reduction in order to make the best use of the available wordlength Clearly dither and noise shaping are irreversible processes the added noise cannot be removed the lost bits cannot be recovered For this reason it makes sense to maintain the longest possible wordlength throughout the production chain and to use dithering or noise shaping as the final step in reducing the wordlength to that of the chosen delivery medium This is particularly true of noise shaping which can be detrimental to subsequent signal processing The problem in maintaining wordlength in the earlier parts of the production chain has often been the lack of availability of long wordlength recorders or transmission paths The ADA 8XR incorporates two alternative methods of extending the wordlength of a digital recorder or transmission channel each of which can be used with either a 16 bit or a 20 bit medium The first Prism Sound MR X is a word mapping or bit splitting system which allows tracks on a multi track medium to be sacrificed in order to make up the extra wordlength The second Prism Sound DRE r
18. 9 4 Menu Pahil onien ati A A E AE LS OA EAAS AAEL 22 6 Adjustments and Upgrades rrrnnnnnnnnnnnnvnnnnnnnennnnnennnnnnnennnr 23 6 1 Changing the mains voltage or fuse ooonnncccinnnnnccinnnnccccnnnorcccnnnorccn anar cnn cnn 23 6 2 Adding l O MOCUICS xc 2c untatt T kiste eee de erme laca 24 6 3 Upgrading the firrmware 2 cccceeccceeeeeeeeeeeeneeeeeeeeeeeeeeeeeeeeneeeeeeaneeneeceeeeeeesenseeee 24 7 Technical Backgroundi rurrnnvnvnnnnnnnnnnnnnennnnnnnennnnnennnnnnnennnr 25 7 1 Synchronization and Jitter iieii roca arranco 25 7 1 1 B ckground undersiden de dd Cdad 25 7 1 2 Why are good clocks SO rare nierirer ie E A nina nn 25 7 1 3 Analysis of sampling ter ee E ER rana 25 7 1 4 Listening EXPpenlENCe cad 26 7 1 5 Synchronization and the ADA 8XR erenrrnnrrvnrennrrnnrennrrrnrennrrenrennrrnsrennrrnssennnnne 26 7 2 Extended sample rates and Split96 interfacing oooooncninnnicococccnnnnocncononcnnnnnnnnnnnnnos 26 7 2 1 What are extended sample rates oooooooconococooooncnnnnnnnnnnononononononnnnnononononnnns 26 7 2 2 What is the use of extended sample rates oooococococcncnononononononononononononononos 27 7 2 3 Interfacing extended sample TateS oooonoonccccnnnccccnnnocccccnnancncnnno cnn nnnno nc n rra nn 27 7 2 4 Extended sample rates in the ADA 8XR 0 cccceceeceeceeeceeeeeceeaeeeeeeeeeeeestsaees 28 7 3 Wordlength dithering and Prism Sound SNS Super Noise Shaping
19. D Prism Media Products Limited 2001 2004 Page 1 19 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 5 2 Meter Panel CNS 15 SJ The Meter Panel fulfils a few different channel related functions First and most importantly it provides eight bargraph meters which can be switched to display the audio levels on all eight channels of either Path through the ADA 8XR Various peak hold and overload modes can be selected within the group of menus reached from the blue Access button Note also that numerical metering of the selected channel or channel pair is normally displayed on the Level Screen the home screen of the Menu display The Path selector button in the top left hand corner of the panel assigns the panel s function to either Path 1 or Path 2 Path 1 is usually the A D Path and Path 2 the D A Path in most standard A D D A configurations but this is flexible The Pre Post button moves the metering position before or after the signal Processing block of the selected Path The Hold button enables or disables an indefinite bargraph peak hold function which also affects the numerical meters on the home screen of the menu display Below the bargraphs are a row of per channel Alert LEDs These provide warning of various notable conditions occuring on the corresponding channel of the selected Path These include digital input lock status analogue input overkiller a
20. a Split96 output to a normal input have occasionally caused embarrassing confusion Prism Media Products Limited 2001 2004 Page 1 27 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 When the 4x sample rates 176 4kHz and 192kHz were first used they were occasionally interfaced in Four wire mode i e with one channel spread across two AES3 carriers However it was more common to use Two wire interfacing at a frame rate of 2x The principle of using a low rate interfaces to carry reduced channel count at extended sample rates is now becoming widespread on interfaces other than AES3 such as MADI or SuperMAC 7 2 4 Extended sample rates in the ADA 8XR The ADA 8XR operates internally at sample rates up to 352 8kHz with 192kHz being the current maximum external PCM rate It can also provide or accept one bit formats such as DSD if required In these matters we are partly at the mercy of the market since presently our own tests have yet to show that sample rates beyond 96kHz provide any audible improvement over well engineered 96kHz sampling It is also our opinion that one bit representations would need to operate at bit rates significantly above those presently proposed in order to match the quality of the ADA 8XR s current 24 bit 96kHz or 192kHz output As with all Prism Sound products the ADA 8XR can transact extended rates 88 2kHz and above in either one
21. ace the screws If the Module cannot be easily seated remove it and try again After adding or removing an I O Module it is advisable to reload the factory stores see the Firmware Reference since some factory configurations depend on Module fitment 6 3 Upgrading the firmware Firmware upgrades are available from your dealer or can be downloaded from the Prism Sound website http www prismsound com Having downloaded the firmware it must be loaded into the ADA 8XR by connecting the ADA 8XR to your computer with an appropriate cable Details of how to do this are included in the readme txt file included with the new firmware O Prism Media Products Limited 2001 2004 Page 1 24 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 7 Technical Background This section provides background information concerning various technical concepts and proprietary Prism Sound processes relevant to the ADA 8XR 7 1 Synchronization and jitter 7 1 1 Background Good clock stability is probably the most important issue separating good quality A D and D A converters from the mass With the linearity of modern converter devices beginning to rival and exceed the performance of the best analogue circuits digital recordings would already be beyond reproach if clock stability did not so often marr potential quality Why is good clock stability so unusual Probably because most conversion equipment has to compromise
22. ains eight LED bargraphs which can be switched to meter either of the two eight channel Paths as well as a row of Channel Select buttons which are used to apply controls to one or more selected channels or to all eight channels using the All button On the right hand side is the Menu Panel which contains the LCD display and navigation keys for the menu system through which all parametric adjustments are made Blue Access buttons distributed over the other three panels provide short cuts into those parts of the menu system related to their positions Below the menu controls are the buttons for the Configuration Store system which allows factory and user defined setups to be instantly loaded At the extreme left hand side of the front panel are the Standby key which is used to switch the ADA 8XR in and out of Standby power mode and below a headphone socket for the two channel Monitor O Prism Media Products Limited 2001 2004 Page 1 10 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 3 2 Rear Panel The rear panel of the ADA 8XR is arranged from left to right when viewed from the rear as follows The mains inlet comprises an inlet socket for the IEC mains lead appropriate regional version provided mains switch and two way voltage selector and fuse holder For details of how to change the voltage selector see section 6 1 To the right of the mains inlet are two lar
23. an be updated to cover new I O Modules O Prism Media Products Limited 2001 2004 Page 1 7 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 2 Getting Started This section is intended to get you going quickly without the need to read the entire Operation Manual This is quite feasible if your application is fairly standard if not you may need to refer to other parts of the manual to get exactly what you need If your ADA 8XR is to be used with a direct workstation interface such as Pro Tools please refer to the appropriate Getting Started section in the Module Reference volume 3 2 1 Connecting the ADA 8XR First check that the line voltage setting matches your local voltage if not change it by reorienting the voltage selector in the power inlet on the rear of the unit Two ranges are selectable 180 250VAC or 90 125VAC Details of how to switch between ranges are in section 6 1 Connections to the analogue inputs and outputs are via panel mounted XLR connectors Connections to digital inputs and outputs may require the use of a breakout cable supplied according to the formats fitted to your unit Direct connection to a workstation may require the use of the workstation manufacturer s cable Refer to the appropriate section in the Module Reference for connection details and example diagrams Analogue Monitor outputs are on RCA phono sockets stereo digital Monitor out is on BNC
24. are updates which will be distributed on disk and via the Internet Although the standard ADA 8XR as summarised above provides eight channels of A D and eight channels of simultaneous D A conversion with a variety of available digital I O options many custom configurations are possible For example the ADA 8XR can be supplied as A D only or D A only at a cost saving or with two A D or D A Modules for sixteen channel operation A two frame 8 in 24 out setup is a popular and cost effective choice for DAW users Another advantage of the modular construction of the ADA 8XR is that future improvements in technology can be incorporated for example new A D converter devices D A converter devices DSP chips digital I O standards can all be accommodated by replacing only the relevant Module 1 3 Firmware Updates The ADA 8XR firmware is stored within the unit in a flash memory which can be updated from a floppy disk or from the Internet Details of how to perform the upgrade are in section 6 3 1 4 Organization of these Manuals The ADA 8XR operators literature is organised as three separate volumes e Operation Manual this volume which covers the general principles of operation e Firmware Reference which provides operating details of the latest firmware revision this volume can be updated in the event of a firmware upgrade e Module Reference which contains information about all available analogue and digital I O Modules this volume c
25. at sampling jitter produces quiet aharmonic components perhaps only subliminally perceptible which marr our impression of the ambience which creates a soundstage Other effects are harder to explain for example there is wide observation that large amounts of sampling jitter can take the edge off extreme bass rendition Such reports are probably too widespread to be ignored but defy explanation within current theory 7 1 5 Synchronization and the ADA 8XR The ADA 8XR is designed to source clocks which are as stable and accurate as possible and also with the aim of being insensitive to the quality of incoming clocks It is designed to remove jitter from any selected reference sync source before it is used as a conversion timebase so as to eliminate any audible effects of sampling jitter whatever sync source is used The ADA 8XR actually contains two independent clock generation and conditioning circuits allowing generation of or synching to two independent sample rates at once Normally one is used for each of the ADA 8XR s two Paths An unusual feature of the ADA 8XR is that a Path can be locked to reference sync sources at different rates from the Path s desired sample rate In this case the ADA 8XR maintains a constant ratio between the reference sync and the Path s sample rate For example if the selected incoming reference sync is identified as being close to 44 1kHz and the Path is explicitly set to sample at 48kHz the Path
26. b LED shows MR X g encoding The Prism Sound MR X encoding scheme is described in detail in section 7 4 The DRE LED shows that one or more of the input channels are being encoded using the Prism Sound DRE Dynamic Range Enhancement format which is a coding scheme to allow extended wordlengths to be recorded on a medium or passed down a digital channel Prism Media Products Limited 2001 2004 Page 1 17 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 WITHOUT sacrificing tracks DRE g is the variant of this format for recorders or data channels with a maximum 16 bit wordlength whereas DRE is used for 20 bit media The 20b LED shows that DRE 9 encoding is taking place whereas the DRE LED without the 20b LED shows DRE encoding The Prism Sound DRE encoding scheme is described in detail in section 7 4 5 1 5 Dest box The Dest Destination box indicates which port s are assigned as the outputs to the selected Path and displays whether digital output ports are operating in Split96 two wire high rate mode The Destination box s Access button attracts the attention of the Menu panel immediately to the small group of menus that control destination related parameters These include assignment of the destination ports themselves adjustment of analogue output gains if an analogue destination port is assigned etc For details of these menus see the Firmware Ref
27. between clock stability operational requirements and cost The ideal clock system in an A D or D A converter would be ultimately stable e would exhibit no sampling jitter at the point of conversion whether operating from an internal clock or from an external synchronization reference of any format and at any sample rate But this is a very tall order for the circuit designer especially one on a budget 7 1 2 Why are good clocks so rare Most converters on the market can provide workmanlike performance when internally clocked since this is only a matter of providing a stable clock oscillator or range of oscillators at a fixed frequency or frequencies although even this is not always well executed The real problem is that in most installations the data converters can almost never operate from their own internal clocks since they must be slaved to a central master reference or in the case of D A converters to their incoming data The externally clocked design challenge is by necessity a trade off since the more stable a clock oscillator is the less is its pull range of frequency adjustment but we would ideally like an oscillator which can operate over a wide range of sample rates perhaps from lt 32kHz to gt 48kHz plus multiples thereof But such an oscillator would inevitably have poor stability at least in terms of the stringent requirements for high quality audio conversion On the other hand if we limit the ranges
28. ceeeeeeeeeeaaeeeseeaeeeseeaeeeeeenaeeeeeeaaes 7 2 Getting Started under ia 8 2 1 Connecting the ADA 8XR rarnsrvnnnnnsrrnnnersrrnnnensrrnnnsrsrrnnssrsrrnnnersrrnnesrsrrnnsersrrnnesnsrreneenn 8 2 2 Configuring the ADA 8XR eerssrvnrervrrnnnersrnnnnersrrnnerrsrrnnerrsrrnnrersrrnneersrrenesrsrrnnsensrrensenn 8 A O 10 3 FFront PANG aa suspekte tii 10 Si2 TO 11 4 Philosophy of Operation rrnrnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnr 12 AA Two Paths iii a a decai 12 4 2 Menus or dedicated Controls oooonncccnnnnncccnnnocccccononnncnnnonnnc nano nc nn cnn narran rca rara 12 4 3 Monitor Mimic Meter and Menu Panels oooonccncccccccconnnnconnnncnnononocnnnanoncnonononeranons 12 4 4 Two channel Monitor sannrrnnrennrrnnnonnrrnnnonnrrnnnennrrnnrennrrensennrrensennrnessennrressennrressennnne 13 4 5 Configuration Stores ieir cece ener ee ee eae ee nano cnn a rr 13 4 6 Warning conditons seccina it dd E 14 5 Control Panel Operation cssicsceccicectccetestecsiteecueshencessueeeicsecse 15 9 15 MIMIC Panel ic iss henv cc cita cti 15 5 1 1 SOCS DOX seii EE EE EEE der EEE 15 5 1 2 TON 16 5 1 3 PROCESS DOX A vs cdebapesga zeus I E dee R peatesaeiadaeaspudzebaevncdeaapeane 17 5 1 4 Dither Encode DOX EEE EEE 17 5 1 5 Dest box OO 18 5 1 6 Sync Source Sample Rate box nmnrrnnrrnnrennrrvnrrnnrrrnnrnnrrnnrennrrenrennrresrrnrrenrrnnnnn 18 9 2 Meter Palit ta EAE REE Ii daa 20 9 32 Monitor Paniel oraaa a aT EAE E AE AAS AE 21
29. ction etc The functions can be multiply selected in the appropriate menu also reached from the Meter Panel Access button so that the LED represents an OR function of the selected functions The Channel Select buttons and the All button are used in conjunction with certain channel specific menus as described in the Module Reference Prism Media Products Limited 2001 2004 Page 1 20 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 5 3 Monitor Panel The Monitor Panel controls the ADA 8XR s two channel monitor MONITOR The Monitor drives both analogue and digital line outputs which are situated on the Utility Panel on the rear of the uw unit The analogue outputs also drive a headphone Pre Post socket on the front For further details see the Utility Module section in the I O Modules section 1 Path 2 The Monitor can be fed from either Path 1 or Path 2 as selected by the Path selector button either pre or post the Path s processing section where available as selected by the Pre Post button Note that the audio output of the Monitor is controlled directly by these buttons the equivalent buttons on other Panels only assign the Panels display The Cut button mutes the Monitor its LED flashing red to indicate the muted state The Invert button phase inverts BOTH of the Monitor s output channels when the orange LED is lit The Mono butt
30. d in a two wire mode whereby a single high rate channel is being carried on a normally two channel interface O Prism Media Products Limited 2001 2004 Page 1 15 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 Note that more than one source LED can be lit this might happen when two Digital I O Modules are cascaded in Split96 mode to provide all eight inputs or when the Input Selection Mode is set to Channel allowing each channel s input to be chosen from more than one assigned port see the Firmware Reference A source LED which is flashing indicates that a selection has been requested which the ADA 8XR firmware cannot accomplish for example a source port may have been assigned which has already been assigned to the other Path The Overkiller LED shows that one or more channels in the Path has its Overkiller progressive analogue limiter switched on For more information about the operation and application of the Overkiller see section 7 5 The Mic and 48V LEDs only apply to Analogue Input Modules with a mic pre facility and indicate that one or more channels in the Path have the mic pre selected and the phantom power turned on respectively 5 1 2 Decode box The Decode box indicates the wordlength of the Path s digital inputs if digital inputs are assigned and also any decode algorithms which are in use The Decode box s Access button attracts the att
31. ding scheme is described in detail in section 7 4 The green LEDs at the left hand side of the box show the effective input wordlength of the input channels Note that the wordlength AFTER any decoding is indicated i e a 24 bit signal being recovered from a 16 bit MR X tape is indicated as 24 bits The indication is made by detecting how many of the low order data bits are held at zero rather than by any other means Note that multiple wordlength LEDs may be lit if different input wordlengths occur simultaneously on different channels Prism Media Products Limited 2001 2004 Page 1 16 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 5 1 3 Process box The Process box indicates whether any of the Path s channels have any functions of the Processing Suite activated The processing Suite is a range of signal processing functions which are available if the DSP Expansion Module is fitted inside the ADA 8XR The Process box s Access button attracts the attention of the Menu panel immediately to the group of menus that control the Processing Suite if it is available otherwise an explanatory message is displayed For details of these menus see the Firmware Reference The Patch LED is lit to indicate that some cross channel patching or mixing is selected The Process LED shows that signal processing functions are active Otherwise the Bypass LED confirms that no patching or processing is enab
32. e currently selected Store is displayed on the top line with the Bank Store number shown below The various stores can be previewed by pressing the Store number buttons 1 6 and the Bank can be advanced by pressing the Bank button The currently selected Store s LED flashes The LCD is returned to it s normal operation by re pressing the flashing Store button 1 6 or by pressing the Menu keys 1 or or by pressing a blue Access button Normal operation is also resumed by the expiry of the menu timeout if enabled The previewed store can be adopted loaded unless empty by pressing Enter Accept Alternatively it can be over written saved or cleared by using the Select Change keys lt or gt to select the required function followed by Enter Accept Clearing a Store requires a confirmation step saving requires the store name to be confirmed or edited followed by a confirmation step When a Store has been loaded that Store s button remains illuminated until any settings are manually changed to indicate that the Store is current At the time of delivery some of the Stores in the first Banks contain factory preset stores covering a range of basic setups depending on the I O Modules fitted to the unit and the remaining Stores are empty However the factory programmed stores are essentially the same as others in that they can be user programmed if re
33. e rate conversion 34 Sampling rate 18 26 Source box 15 Specifications 36 Split96 27 Standby key 10 Store system 13 Stores 22 Supe Noise Shaping SNS 29 Swap button 21 Sync source 18 Sync Source Sample Rate box 18 Synchronization 25 Synchronous sample rate conversion SSRC 34 Truncation 28 Two wire interfacing 27 Utility Module 11 Voltage selector 11 23 Volume control 21 Warnings 14 Wordlength 16 28 Page 1 40
34. early channels on the medium it is possible to use the early channel meters on for example a multi track tape recorder to monitor audio levels in the usual way However don t be surprised to see random deflections on the other channels meters these indicate the presence of the secondary tracks and tag Obviously for correct reconstruction of the audio data it is important that the replay or transmission path includes all eight tracks otherwise an incorrect Track Mode might be decoded or low order bits lost This makes it inadvisable to record tracks individually or at different times on a multi track tape recorder although with care it can be done In the four channel mode record channels 1 and 5 together channels 2 and 6 together etc channels 4 and 8 should be recorded first to lay down a continuous Track Mode tag In the six channel modes channels 1 3 5 and 7 should be recorded together with channels 2 4 6 and 8 recorded first to lay down the tag Note that MR X is not supported by the ADA 8XR at the 4x sample rates 176 4kHz and 192kHz It is uncommon to find 4x recorders or channels which do not support full 24 bit operation 7 4 3 Prism Sound DRE Dynamic Range Enhancement Prism Sound DRE Dynamic Range Enhancement was devised as an encoding scheme for representing extended wordlengths on a 16 bit recorder or transmission channel but without the need to sacrifice channels This requirement obvious
35. en much discussion as to whether the presence of high frequencies which would be imperceptible alone can cause changes to the rendition of lower frequencies Perhaps a more likely explanation for the improvement in perceived quality at higher sample rates cites implementation limitations of the digital or analogue anti aliasing filters within current off the shelf converter devices These filters have traditionally been designed with very sudden high frequency roll off in order to maximise the available audio bandwidth at barely adequate sample rates This requirement coupled with practical limitations in filter complexity have led to compromised designs with significant ripple in the passband and sometimes inadequate attenuation in the stop band In addition these very steep filters often result in unwanted temporal distortion i e discrete pre and post echo effects There is speculation as to why and how these might be noticeable but experiments carried out with no compromise filter designs at traditional sample rates which eliminate these echoes suggest that their removal renders the sampled signal subjectively indistinguishable from the original analogue So perhaps very extended sample rates are not strictly necessary on the other hand an inadequate filter operating at extended rates produces echoes proportionately nearer in time to the actual signal than it does at lower rates which are likely to be less noticeable If this
36. ention of the Menu panel immediately to the small group of menus that control the available decoding algorithms For details of these menus see the Firmware Reference The MR X LED shows that the input port is being decoded from the Prism Sound MR X format which is a word mapping scheme whereby for example a multi channel digital recorder can be used to record longer wordlengths and or higher sample rates than its native format by sacrificing tracks MR X g is the variant of this format for recorders or data channels with a maximum 16 bit wordlength whereas MR X2 is used for 20 bit media where less track sacrificing results The 20b LED shows that MR X2p decoding is taking place whereas the MR X LED without the 20b LED shows MR X g decoding The Prism Sound MR X encoding scheme is described in detail in section 7 4 The DRE LED shows that one or more of the input channels are being decoded from the Prism Sound DRE Dynamic Range Enhancement format which is a coding scheme to allow extended wordlengths to be recorded on a medium or passed down a digital channel WITHOUT sacrificing tracks DRE is the variant of this format for recorders or data channels with a maximum 16 bit wordlength whereas DRE is used for 20 bit media Note however that the decoding algorithm is common for DRE and DRE data so it is not necessary to distinguish which is to be decoded The Prism Sound DRE enco
37. equires no track sacrifice and so can be used on stereo media however unlike MR X DRE does not guarantee to preserve the precise input data Both encoding schemes must be decoded in order to reconstitute the audio signal The necessary decoders are also included in the ADA 8XR 7 4 1 Prism Sound MR X Originally featured on the Prism Sound MR 2024T Interface Adapter for Tascam DA 88 the MR X encoding system became a de facto standard for storing 20 bit and 24 bit audio on MDMs When the need to pass CD targetted material with extended wordlength to mastering studios was recognised the SYSTEM MR X format provided at that time the only cost effective medium which was accepted by the world s top mastering Prism Media Products Limited 2001 2004 Page 1 31 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 facilities MR X is also licensed to other manufacturers of compatible products The original MR X format was targetted at eight channel 16 bit recording or transmission media and allowed the medium to be used as Eight 16 bit channels native mode or Six 20 bit channels or Four 24 bit channels The ADA 8XR also features an extended mode of MR X for eight channel 20 bit media which allows the medium to be used as e Eight 20 bit channels native mode or e Six 24 bit channels In view of this extension to the format the original MR X for 16 bit media is now referred to as MR X
38. erence The green LEDs at the right hand side of the box show which output ports have been assigned to the Path These comprise Analogue Module Slot 1 or 2 outputs or Digital Module Slot 1 or 2 outputs The Split96 indicators show when digital outputs are being used in a two wire mode whereby a single high rate channel is carried on a normally two channel interface Note that more than one destination LED can be lit this might happen when two Digital I O Modules are cascaded in Split96 mode to provide all eight outputs or simply when multiple output ports have been assigned to the Path as parallel outputs A destination LED which is flashing indicates that a selection has been requested which the ADA 8XR firmware cannot accomplish for example a destination port may have been assigned which has already been assigned to the other Path 5 1 6 Sync Source Sample Rate box The Sync Source Sample Rate box indicates the synchronization state of the Path Its Access button attracts the attention of the Menu panel immediately to the small group of menus that control the various synchronization options For details of these menus see the Firmware Reference The six LEDs on the left hand side of the box indicate the selected synchronization source Local is the ADA 8XR s internal crystal reference WCK AES and Video refer to various synchronization input connectors on the Utility Module at the right hand
39. extended processing features including synchronous sample rate conversion e Modular architecture allows special configurations e g 16 channel D A or A D unit Comprehensive store system for fast access factory and user presets e Unique Access button layout combines flexibility of menus with speed of dedicated controls e Modular architecture provides future proofing A D conversion D A conversion DSP digital interfacing and utility hardware can all be individually upgraded 1 1 Functionality The ADA 8XR provides eight channels of high resolution high sample rate A D and D A conversion with a variety of processing and interfacing functions plus a two channel Monitor with both analogue and digital outputs A D and D A Paths can be independently synchronized at 32 44 1 48 88 2 96 176 4 or 192kHz sample rates Sync sources can be Local WCK AES11 or DI one of the digital inputs and can be at a different rate from the Path s sample rate if required Wordlengths of 16 20 and 24 bits are supported Digital output wordlength is managed by flat re dithering or by applying one of the family of industry standard Prism Sound SNS noise shaping algorithms Bit splitting using the Prism Sound MR X system as implemented on the Prism Sound MR 2024T interface adapter and licensed equipment from other manufacturers is built in so that 20 bit and 24 bit recordings at up to 96kHz can be made and replayed using 16 bit low sample ra
40. f the Menu Panel until the desired Bank of Stores is shown in the LCD display Then press the desired Store number button At this point the name and number of the desired Store should be displayed along with the message Load Press the Enter Accept key to load the Store If the Store you loaded requires further modification the easiest way to do this is to use the blue Access buttons which are distributed over the ADA 8XR s Front Panel The Access buttons on the Mimic Panel block diagram area are the most likely to be useful Using the Path select button in the top left hand corner of the Mimic Panel choose the Path who s Prism Media Products Limited 2001 2004 Page 1 8 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 settings you want to modify Normally Path 1 is configured as the A D Path and Path 2 as the D A Path although other variations are possible check that you are dealing with the desired Path by observing the signal flow indicated by the LEDs on the Mimic Panel in each of the states of the Path selector button Choose the appropriate Access button to take you to the first parameter you want to alter For example if you want to change something to do with the analogue input of an A D Path press the Access button in the Source box This action takes the Menu Panel with the LCD display directly to the cluster of Menus which deal with the analogue inp
41. ge Module Slots for Analogue I O Modules The upper slot is referred to as Analogue I O Slot 1 or AlO1 in the front panel legends and menus Inputs on Analogue Module 1 are referred to as Al1 outputs as AO1 The lower slot is Analogue I O Slot 2 with similar nomenclatures To the right of the Analogue I O Slots are two small Module Slots for Digital I O Modules The upper slot is referred to as Digital I O Slot 1 or DIO1 in the front panel legends and menus Inputs on Digital Module 1 are referred to as DI1 outputs as DO1 The lower slot is Digital I O Slot 2 with similar nomenclatures On the extreme right hand side is the Utility Module which contains a variety of input and output connectors for Reference Sync analogue and digital Monitor and serial communications Details of all available Analogue and Digital I O Modules including the Utility Module are in the Module Reference Prism Media Products Limited 2001 2004 Page 1 11 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 4 Philosophy of Operation 4 1 Two Paths The ADA 8XR has two Paths each comprising eight channels these are typically an A D Path and a D A Path but not necessarily so The Monitor Mimic and Meter panels each have a Path selector button so that their function can be swapped between the Paths The Path selector buttons on these panels are independent so you can monitor one Path while metering the
42. ged in software This is generally also true of the I O Modules but any user adjustments that might apply are detailed in the Module Reference 6 1 Changing the mains voltage or fuse The mains line fuse and the mains voltage selector are carried within the IEC inlet on the rear of the ADA 8XR The required fuse is a 2AT 20x5mm type The voltage selector has two positions 115V covers the range 90VAC to 130VAC and 230V covers the range 180VAC to 260VAC The diagram below shows how to replace the fuse or change the voltage selection Lever up the voltage selector fuse holder cover by inserting a small flat bladed screwdriver into the slot as shown Remove the red plastic holder If replacing the fuse use a 2AT 20mmx5mm type and having placed it in the same location as the old fuse replace the red plastic holder in the same orientation as before with the selected voltage AWAY from the switch and close the cover To change the mains voltage selection orient the red plastic holder with the desired voltage uppermost as shown in the diagram below It is necessary to swap the positions of the fuse and a small metal clip on the opposite side of the holder The correct side and location for each is shown in the diagram Replace the red plastic holder in the new orientation with the selected voltage AWAY from the switch and close the cover Check that the desired voltage is visible through the window Note that unless the holder
43. h multi channel media by word mapping or bit splitting Channels are sacrificed to hold the extended parts of the audio samples A sophisticated dithering technique whereby the requantization error is filtered and subtracted from the input data The filter is designed so that the resulting noisefloor is optimally shaped in frequency so as to be as inaudible as possible See also Truncation Dither Page 1 38 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 One wire Overkiller Reference Sync Sampling Jitter Sample Rate n Z n Split96 SSRC Superclock Truncation Two wire Wordclock Wordlength An AES3 interface carrying extended sample rate audio by using an increased bit rate Two channels can be represented just as at low sample rates A proprietary Prism Sound device which progressively limits transients ahead of an A D converter allowing better use of dynamic range and louder recording levels A signal passed between digital audio equipment to ensure that all work at identical sample rates Jitter in the timing of an A D or D A converter or within a sample rate converter which causes unpleasant aharmonic distortion in the converted audio signal The rate at which digital audio samples are produced by an A D converter Higher sample rates allow a wider range of input frequencies to be represented in the digital signal Super Noise Shaping
44. ice of noise shaper is the one which sounds best for the material The Prism Sound SNS logo shown above is found on many of the world s finest CDs and is recognised as a standard of technical excellence The logo and accompanying sleeve note is available by contacting sales prismsound com 40 SNS noise spectra for 16 bit output 44 1kHz sampling rate 30 Pa ae 20 pee woe a 10 ifr dB D Flat dither vf O x ee i Fo SNS1 EE aa 46 EE armen ea anes TER 27 EA ee gt SNS4 20 LL eae SNS3 gt 30 I I I l 0 2k Ak Sk Sk 10k 12k 14k 16k 18k 20k 22k Frequency HZ 40 SNS noise spectra for 16 bit output 48kHz sampling rate s30 gt gt gt Flat dither of SNS1 RN E 20 SNS3 A 30 I I l l l 0 2k 4k Bk Sk 10k 12k 14k 16k 18k 20k 22k Mk Frequency Hz Prism Media Products Limited 2001 2004 Page 1 30 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 30 SNS noise spectra for 16 bit output 96kHz sampling rate 20 10 Flat dither 0 dB 40 SNS1 gt p SNSZ SNS3 20 se de T p Eos oo SNSA gt 30 fof 40 0 5k 10k 15k 20k 25k 30k 35k 40k 45k Frequency Hz Note that no wordlength reduction is supported by the ADA 8XR at the 4x sample rates 176 4kHz and 192kHz The wordlength is fixed at
45. ich have given sample rate converters their characteristic sound in the past The Prism Sound SSRC is included with the DSD I O Module and allows simultaneous rate conversion of all eight channels between any two PCM sample rates from 32 44 1 48 88 2 96 176 4 and 192kHz 7 7 References The following references provide additional information about the technical background topics J Watkinson The Art of Digital Audio gr Edition Focal Press ISBN 0 240 51587 0 L D Fielder Human auditory capabilities and their consequences in digital audio converter design from Audio in Digital Times AES Conference New York 1989 J Vanderkooy S P Lipshitz Digital Dither Signal Processing with Resolution Far Below the Least Significant Bit from Audio in Digital Times AES Conference Toronto 1989 M Gerzon P G Craven Optimal noise shaping and dither of digital signals Preprint 2282 presented at the 87 AES Convention New York September 1989 N J Dunn G Demnis The Diagnosis and Solution of Jitter Related Problems in Digital Audio Systems Preprint 3868 presented at the 96th AES Convention Amsterdam February 1994 S Yoshikawa S Noge T Yamamoto K Saito Does High Sampling Frequency Improve Perceptual Time Axis Resolution of Digital Audio Signal Preprint 4562 presented at the 103 AES Convention New York September 1997 N J Dunn Anti alias and anti image fi
46. led 5 1 4 Dither Encode box The Dither Encode box indicates the wordlength of the Path s digital outputs if digital outputs are assigned and also any encode algorithms which are in use The Dither Encode box s Access button attracts the attention of the Menu panel immediately to the small group of menus that control output wordlength and encoding algorithms For details of these menus see the Firmware Reference The column of green LEDs in the middle of the box show the wordlength of the digital audio channels being output More than one of these LEDs might be illuminated if more than one wordlength range has been selected for different output channels of the Path The SNS LED to the left is illuminated if any of the channels has has wordlength reduction using the Prism Sound Super Noise Shaping algorithm selected The Flat LED is lit if any of the Path s channels have only flat dither selected The Prism Sound Super Noise Shaping process is described in detail in section 7 3 The Auto LED is lit to indicate that Auto Dither Defeat is active Auto Dither Defeat is an algorithm which prevents unnecessary or undesirable dithering or noise shaping being applied to the channels of a digital to digital Path This happens in one of two situations Firstly if the incoming wordlength is less than or equal to the desired output wordlength it is unnecessary to add further dither or noise shaping since no truncation of the
47. lly Path 1 shows an analogue input connected through some processing past a monitoring and metering point through some encoding and out through a digital output Naturally there are countless settings which affect this Path buried in the menu system On the Mimic panel are a selection of blue Access buttons each one conveniently located in one of the functional areas of the Mimic If you press an Access button you immediately attract the attention of the Menu panel to the particular menu which controls that function and the nearby blue LED lights to show that that is happening Actually there may be several menus which apply to that Access button if the first menu isn t the right one press the Access button again and you can cycle round the small number of relevant menus If you use the same menu a lot don t worry next time you use that Access button you go straight to the menu you were using last time you were in that Access group The Monitor and Meter panels also have an Access button which are used to get to their parts of the menu system fast In the Meter panel under each channel s meter is a Channel Select button normally this is used to monitor that pair of channels or to select or deselect the channel if the Monitor is in Prism Media Products Limited 2001 2004 Page 1 12 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 Mix mode But in menus where settings need to
48. ltering the benefits of 96kHz sample rate formats for those who cannot hear above 20kHz Preprint 4734 presented at the 104 AES Convention Amsterdam 1998 S P Lipshitz J Vanderkooy Why Professional 1 bit Sigma Delta Conversion is a Bad Idea Preprint 5188 presented at the 109 AES Convention Los Angeles September 2000 Prism Media Products Limited 2001 2004 Page 1 35 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 8 Specifications This section contains the specification for the ADA 8XR Mainframe specifications for Analogue and Digital I O Modules are contained in the Module Reference Unless otherwise stated all performance specifications are rms unweighted band limited 20Hz 20kHz sampling at 96kHz wordlength 24 bits analogue I O line up at OdBFS 18dBu 8 1 Physical Dimensions Width 435mm 483mm overall including rack mounts Depth 390mm Height 88mm Power supply 90 125 180 250VAC 50 60Hz External line switch voltage selector and fuse Consumption 60W Module Slots 2 x Analogue I O Module Slots 2 x Digital I O Module Slots 1 x Utility Module Monitor outputs ref sync I O and RS232 485 MIDI comms 8 2 Synchronization Independent multi stage auto ranging PLL sync circuits for each Path Ultra high precision mode within 0 15 of standard rates Jitter rejection corner frequency 80Hz Jitter rejection slope 60dB decade Jitter attenuation gt 60dB ab
49. ly means that precise data cannot be reconstituted under all circumstances DRE works by ensuring that precise data IS reconstituted for small and moderate signal levels up to about 20dB below peak and that loss of data is optimally concealed above that point This criterion was in response to existing sub band perceptual coding systems which have unsatisfactory small signal performance Subjectively DRE allows 16 bit media such as DAT or CD R to be used to make recordings indistinguishable from 20 bit recordings The ADA 8XR also features an extended version of DRE optimised for use with 20 bit media In view of this extension to the format the original DRE for 16 bit media is now referred to as DRE 5 and the new extension for 20 bit media is known as DRE o 7 44 Using Prism Sound DRE with the ADA 8XR DRE encoding is selected within the Dither Encode box of the Mimic Panel as described in section 5 1 4 DRE encoding is indicated by the DRE LED being lit if the 20b LED beneath is also lit DRE29 encoding is indicated otherwise DREg encoding is indicated When selecting DRE encoding DRE 1g or DRE29 mode must be explicitly selected DRE decoding is selected within the Decode box of the Mimic Panel as described in section 5 1 2 DRE decoding is indicated by the DRE LED being lit Note that the decoding algorithm is common for DREy and DRE data so it is not necessary to distinguish which is to be decoded Note tha
50. n this it is possible to select a different sample rate from that of the designated reference sync For example you could select an external Wordclock as a Path s sync source and also Prism Media Products Limited 2001 2004 Page 1 18 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 specify 48kHz explicitly as the desired sample rate In this case the external wordclock frequency is continually measured by the ADA 8XR and an assessment is made as to whether it is within an acceptable tolerance of a standard sample rate and if so what the rate is If the rate of the Wordclock is say close to 44 1kHz then the ADA 8XR will assume it to be the house 44 1kHz and will use it to sync the Path BUT THE PATH WILL STILL RUN AT 48kHz or more precisely at 480 441 times the reference rate In this case the Ext LED would not be lit If it is desired that the Path s sample rate should always reflect the sample rate of the ref sync then Ext should be selected in the sample rate menu For more details of these menus see the Firmware Reference It is not uncommon to see flashing LEDs in the Sync Source Sample Rate box A flashing LED indicates a requested state which could not be met For example if an external AES reference was selected but no such ref sync input is detected by the ADA 8XR it substitutes a local clock reference automatically lights the Local LED and flashes the AES LE
51. n the acclaimed range of Prism Sound Dream A D and D A converters which have become widely regarded as the world s best sounding converters Whilst continuing the tried and trusted no compromise design philosophy of previous Dream products the Dream ADA 8XR adds a new dimension in flexibility functionality and cost effectiveness e Eight channels of high performance 24 bit A D conversion e Eight channels of high performance 24 bit D A conversion Sample rates up to 192kHz e Modular digital I O options include popular interface standards and direct workstation connections e Two channel Monitor section follows channel pairs or a mix of all channels e Prism Sound Overkiller progressive limiting of each A D channel e Prism Sound Super Noise Shaping on each channel e Precise and repeatable software controlled analogue input and output line up levels Eight channel assignable bargraph meter array with over detection Renowned Prism Sound jitter rejecting PLL technology and low jitter master clock e Flexible synchronization options including sync to AES11 wordclock or video sync e Flexible routing allows creation of D D processing Paths for processing or format conversion e Prism Sound MR X bit splitting allows extended wordlengths and sample rates on 16 bit media e Prism Sound DRE allows extended wordlength performance on 16 bit stereo media e Optional DSP expansion facility for
52. ndicators on the Mimic Panel are arranged in an array of functionally separate boxes as described below Each of these functional boxes has a blue Access button which takes the ADA 8XR s menu system directly to the small group of menus which apply to that box s function pressing the Access button repeatedly cycles through the menus specific to that box For details of these functions see the Firmware Reference Note that the menus reached by pressing the Access buttons can also be reached but not so quickly or conveniently by navigating the menu system in the normal way An Access button s LED is lit whenever one of its associated menus is active even if that menu was not activated by the Access button 5 1 1 Source box The Source box indicates which port s are assigned as the inputs to the selected Path and displays other input related parameters The Source box s Access button attracts the attention of the Menu panel immediately to the small group of menus that control source related parameters These include assignment of the source ports themselves adjustment of analogue input gains if an analogue source port is assigned etc For details of these menus see the Firmware Reference The green LEDs at the left hand side of the box show which input ports have been assigned to the Path These comprise Analogue Module Slot 1 or 2 inputs or Digital Module Slot 1 or 2 inputs The Split96 indicators show when digital inputs are being use
53. nsmitted on a coaxial cable The number of bits in a digital audio sample Prism Media Products Limited 2001 2004 Page 1 39 Prism Sound ADA 8XR Multi channel A D D A Converter Index Ext LED 18 Access buttons 12 22 AES EBU 38 AES3 38 Alert LEDs 20 Analogue l O slots 11 Auto Dither Defeat 17 Auto LED 17 Bank button 13 Blue Access buttons 22 Channel Select buttons 20 Clocking 25 Configuration Stores 13 22 Cut button 21 Decode box 16 Destination box 18 Digital I O slots 11 Dither 28 Dither Encode box 17 DRE encoding 16 17 33 DSP Expansion Module 17 Extended sampling rates 26 Firmware 7 Firmware upgrading 24 Flashing LEDs 14 19 Front panel layout 10 Functionality 6 Fuse 23 Getting started 8 Headphone socket 10 Hold button 20 I O Modules adding and removing 24 Invert button 21 Jitter 25 Mains inlet 11 23 Menu Panel 10 12 22 Menu system 22 Menus 12 Meter Panel 10 12 20 Mimic Panel 10 12 15 Prism Media Products Limited 2001 2004 Operation Manual Revision 1 00 Modularity 7 Monitor 13 21 Monitor connectors 21 Monitor Mixed mode 21 Monitor Pairs mode 21 Monitor Panel 10 21 Mono button 21 MR X encoding 16 17 31 Noise shaping 29 One wire interfacing 27 Overkiller 16 34 Path concept 12 Paths 12 Process box 17 Processing Suite 17 Rear panel layout 11 Reload factory stores 22 Sampl
54. o take into account the number and location of the various I O Modules However it is helpful to follow the same conventions that apply to factory fitted Module options as follows Where both Analogue Input and Analogue Output Modules are fitted the Input Module is fitted to AlO1 and the Output Module to AlO2 Where both general purpose and Workstation Digital I O Modules are fitted the Workstation Module is fitted to DIO1 and the general purpose I O Module to DIO2 It is not strictly necessary to follow this convention but to do so eases comparison with example configurations discussed in the manuals To remove an existing Module or blanking plate first remove the small screws which secure it Analogue Modules have nine screws five at the top of the panel four at the bottom Digital Modules have five screws three at the top of the panel two at the bottom It should now be possible to gently easy the Module out of its slot some Modules are more easily removed by plugging in one or more connectors and gently pulling the mating connectors NOT the cables to remove the Module To fit the new Module ensure that the edges of the Module locate in the plastic guide rails within the Module Slot and push the Module gently home The Module should slide easily to within about 10mm of its final position after which firm pressure is needed to seat the Module in its edge connector With the Module end plate resting against the ADA 8XR rear panel repl
55. of the Mimic Panel as described in section 5 1 2 MR X decoding is indicated by the MR X LED being lit if the 20b LED beneath is also lit MR X2 decoding is indicated otherwise MR X1g5 decoding When selecting MR X decoding it is sufficient simply to select the Auto mode in this state MR X or MR X29 modes and the particular Track Mode are automatically selected depending on the identification tag of the incoming data In the extended precision non native Track Modes the audio data for each channel is split into primary and secondary tracks The primary track contains the most significant 16 or 20 bits of each sample with the remainder being placed in the secondary track In the six channel Track Modes the primary tracks for channels 1 6 occupy channels 1 6 of the medium respectively with the secondary tracks for channels 1 3 and 5 in channel 7 of the medium and for channels 2 4 and 6 in track eight of the medium In the four channel Track Mode the primary tracks for channels 1 4 occupy channels 1 4 of the medium respectively with the secondary tracks for channel 1 in channel 5 of the medium for channel 2 in channel 6 of the medium and so on The Track Mode identification tag is always contained in channel 8 on the medium Prism Media Products Limited 2001 2004 Page 1 32 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 Since the primary tracks always occupy the
56. on causes the two Monitor channels to be mixed together at both outputs when its LED is lit The Swap button exchanges the Monitor s A and B channel outputs when its LED is lit A volume control is available if required although this can be defeated from within the Monitor options menus The blue Access button at the top of the panel causes the menu system to enter a small range of menus which apply to the two channel Monitor These menus control various auxiliary functions such as analogue line up level headphone cut volume control enable disable etc as well as allowing selection of the Monitor operating mode In Pairs mode the adjacent channel pairs are monitored whereas in Mixed mode a mix of any of the Path s channels can be created each with its own gain and pan setting Separate mixes are retained for each Path which are selected when that Path is monitored For full details of the Monitor related menus see the Firmware Reference Prism Media Products Limited 2001 2004 Page 1 21 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 5 4 Menu Panel The Menu Panel provides manual control and inspection of all the ADA 8XR s operating parameters and also contains the Configuration Stores buttons for loading and saving setups of the ADA 8XR The operation of the Menu system is detailed in the Firmware Reference In I general the Menu keys t and
57. ove 700Hz High precision mode within 6 00 of standard rates Allows sync to analogue tape and varispeed Internal references at 32 44 1 48 88 2 96 176 4 192kHz 25ppm Sync sources include internal crystal wordclock AES11 video or any digital input Paths can sample at a different rate from their sync source if required Wordclock and AES11 sync outputs can be driven by either Path Superclock output mode available to slave Digidesign 888 24 I O units fs 2 fs 4 loop sync available for use with Pro Tools HD systems Prism Media Products Limited 2001 2004 Page 1 36 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 8 3 Monitor Two channel analogue and digital assignable to either Path by channel pair or mixed Function keys for volume mute mono channel swap and phase invert Analogue outputs Electronically balanced on RCA phono connectors Output impedance 500 Four software controlled output ranges OdBFS 15 18 21 or 24dBu Absolute gain accuracy 0 05dB THD n 997Hz 1dBFS 101dB 0 0009 rms unweighted Dynamic range 997Hz 60dBFS 105dB rms unweighted Channel separation 1kHz gt 120dB 20Hz 20kHz gt 105dB Headphone output 6 3mm stereo jack output impedance 1140 Four sensitivity ranges max 4 7Vp p Digital output AES3 id S P DIF jumper selectable on Utility Module see volume 3 24 bits channel status as defined by firmware revision see volume 2 8 4 Me
58. quely progressive manner which gives it unrivalled capacity to soak up large transient overloads without any noticeable distortion whilst protecting the A D converter from overmodulation There is no need for the Overkillers thresholds to be manually adjusted the ADA 8XR s software automatically adjusts the thresholds according to the selected analogue line up level and trim 7 6 Sample rate conversion and Prism Sound SSRC Sample rate converters have a bad name amongst audio engineers They are regarded as sounding so bad that it is often preferred to rate convert through analogue using good quality D A and A D converters The Prism Sound Synchronous Sample Rate Converter SSRC brings new quality to the rate conversion process The plot below shows a 997Hz tone at 1dBFS being converted from 96kHz sample rate to 44 1kHz sample rate by Prism Sound SSRC in the ADA 8XR 0 24 THD n 137 50dBFS 48 Maximum spurium 151 65dBFS at 2196 34Hz 72 dBFS 96 120 144 168 192 0 2k76 5k51 8k27 11k03 13k78 16k54 19k29 22k05 Frequency Hz O Prism Media Products Limited 2001 2004 Page 1 34 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 As can be seen from the plot the largest spurious component is at 151 65dBFS which represents a huge improvement over competitive asynchronous rate converters whose imprecise conversions produce large and obtrusive aharmonic distortion components wh
59. quipment THIS DIGITAL APPARATUS MEETS ALL CLASS B LIMITS FOR RADIO NOISE EMISSIONS AS LAID DOWN IN THE RADIO INTERFERENCE REGULATIONS OF THE CANADIAN DEPARTMENT OF COMMUNICATIONS CET APPAREIL NUM RIQUE RESPECTE TOUTES LES EXIGIENCES APPLICABLES AUX APPAREILS NUM RIQUES DE CLASSE B SUR LE BROUILLAGE RADIOELECTRIQUE EDICTE PAR LE MINISTERE DES COMMUNICATIONS DU CANADA EN55103 1 environment category E4 Prism Media Products Ltd hereby declares that this equipment conforms to the following standards EN55103 2 environment category E4 NOTE The use of this equipment with non shielded interface cabling is not recommended by the manufacturer and may result in non compliance with one or more of the above directives All coaxial connections should be made using a properly screened 750 cable with the screen connected to the outer of the connector at both ends All XLR connections should use a screened twisted pair cable with the screen connected to pin 1 of the XLR connector at both ends In the case of the digital XLR connections this cable should be of 1100 impedance O Prism Media Products Limited 2001 2004 Page 1 3 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 Contents 1 Introduetona22vassasssansseenmesnsnantesuen 6 L NA 6 4 22 Modularity ics cotati sen eundeetiedl A deel en dnd 7 13 Firmware Upd tesayuu fear A ec iaa 7 1 4 Organization of these Manuals c cccececeeeeeeeeneeee
60. quired If after reprogramming it is desired to return these Stores to their factory default settings this can be achieved through the Preferences menu The Factory Default Stores loaded will reflect the I O Modules fitted at the time of the reload The user can select whether or not analogue I O line up gains and trims and the state of the Monitor are to be recalled with Stores or not by using submenus within Preferences Prism Media Products Limited 2001 2004 Page 1 13 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 4 6 Warning conditions It is possible to set operating parameters in the ADA 8XR which are mutually conflicting or which cannot be met for other reasons For instance if the analogue outputs are assigned to both Paths or if an external reference sync is specified but is not connected then the ADA 8XR must deal with the resulting situation In these cases warnings are generated Warnings are indicated by a flashing LED and possibly the solid illumination of an additional LED For example in the case of an unconnected external reference sync local sync will be automatically substituted and this state will be shown by the Local LED being lit and the LED of the intended external sync being flashed In general solidly lit LEDs indicate what is actually happening and flashing LEDs indicate what has been requested but cannot be implemented If any warnings are active a ro
61. s sample rate will follow the reference rate multiplied by 48000 44100 7 2 Extended sample rates and Split96 interfacing 7 2 1 What are extended sample rates Sample rates above 48kHz are often referred to as extended sample rates Selecting an extended sample rate for an A D Path allows the inclusion of higher audio frequencies in the O Prism Media Products Limited 2001 2004 Page 1 26 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 converted data up to a maximum just short of half the selected rate In the case of D A or D D Paths the choice of sample rate is usually made for us since incoming data has already been sampled at a particular rate 7 2 2 What is the use of extended sample rates Whether the inclusion of extended audio frequencies in an A D conversion i e above the 20kHz ish imposed for say 44 1kHz sampling is beneficial is still being debated The general listener opinion is that it really does give improved sound quality although it is worth bearing in mind that nearly all comparative tests have tended to involve setups where A and B differ by far more than just the sample rate Assuming then that there is an improvement there is much disagreement as to why this might be There is little or no scientific evidence to suggest that anyone can hear sounds above about 25kHz with sensitivity above 20kHz being non existent for the vast majority There has be
62. t DRE encoded data cannot be metered accurately at the recorder or transmission channel Although the audio envelope is approximately maintained in the encoded data levels are not as metered Note that DRE is not supported by the ADA 8XR at the 4x sample rates 176 4kHz and 192kHz It is uncommon to find 4x recorders or channels which do not support full 24 bit operation Prism Media Products Limited 2001 2004 Page 1 33 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 7 5 Prism Sound Overkiller The Prism Sound Overkiller is a progressive analogue peak limiter which can be applied to any of the ADA 8XR s analogue input channels so long as a suitably equipped Analogue Input Module is fitted The Overkiller allows analogue input signals far above the normal maximum handling level of the A D converter to be accommodated without causing the converter to clip This is done in a gentle and progressive manner so that distortion is as inaudible as possible This is useful in certain situations For example it may be desirable for a digital recording to be made louder than would be possible if its loudest transients had to be accurately represented on the digital medium Or where the dynamic range of the recording medium is limited and perhaps levels are not easily controlled such as when recording a live performance onto DAT In these situations the Prism Sound Overkiller acts in a uni
63. te recorders Encoding and decoding of Prism Sound s DRE process extended wordlength recording on 16 bit media without sacrificing tracks is also included Digital I O for high sample rates can be in 1 wire or 2 wire Split96 format Analogue inputs can be individually aligned in software for OdBFS levels of 5dBu to 24dBu in 0 5dBu steps with 0 5dB trim in 0 05dB steps The Prism Sound Overkiller progressive limiter feature is selectable per analogue input channel to allow louder tape levels by control Prism Media Products Limited 2001 2004 Page 1 6 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 of transients Analogue outputs can also be individually aligned for OdBFS levels of 5dBu to 24dBu in 0 5dBu steps with 0 5dB trim in 0 05dB steps A two channel Monitor is provided which can be attached to either the A D or D A Path it can monitor either adjacent channel pairs or a mix of any or all of the channels with individual gain and pan settings The Monitor has both analogue line and headphone and digital outputs Digital to digital Paths can be set up for dithering noise shaping or MR X DRE encoding decoding and or converting between different interface formats 1 2 Modularity The ADA 8XR is modular in respect of both its hardware and software Throughout the life of the product new software features and support for new hardware options will be added through firmw
64. ters Eight channel bargraph plus two channel digital readout assignable to either Path Manual hold function Overload indicator threshold OdBFS or 0 05dBFS Assignable Alert function 8 5 DSP Standard processes Encode for digital outputs Wordlength reduction Flat dither or one of four Prism Super Noise Shaping SNS algorithms Intelligent auto dither defeat system Prism MR X mapping 20 bit 24 bit hi rate on 16 bit tracks 24 bit hi rate on 20 bit tracks Prism DRE 20 bit dynamic range on 16 bit tracks or 24 bit dynamic range on 20 bit tracks without loss of tracks Decode for digital inputs Prism MRX and DRE as above Expansion processes with additional DSP Module as detailed in the Firmware Reference Prism Media Products Limited 2001 2004 Page 1 37 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 9 Glossary ADAT AES3 AES EBU DARS Dither Interface Jitter Jitter Lightpipe MADI Noise Shaping O Prism Media Products Limited 2001 2004 An optical eight channel digital audio interface format first used in Alesis ADAT recorders A two channel digital audio interface format complying with the AES3 standard See MADI A Reference Sync format complying with the AES11 standard similar to an AES3 carrier Also known as DARS Digital Audio Reference Signal See AES3 See AES11 A technique
65. theory proves to be correct it will cast doubt on the usefulness of the 4x rates e g 176 4kHz or 192kHz and above since the transition band is already comfortably wide enough at 96kHz to eliminate echoes with cheaply realisable filters rolling off comfortably beyond audible frequencies 7 2 3 Interfacing extended sample rates When extended sample rates were first experimented with it was difficult to operate the preferred AES3 interface format at twice its normal rate not that difficult actually but existing interface devices wouldn t work and so early 96kHz equipment used two AES3 interfaces each running at 48kHz instead of carrying a stereo signal each interface carried one channel with its odd and even samples placed as if left and right Although offensive to engineering types this approach had unexpected advantages operationally you could use your existing AES3 routers and multi channel recorders albeit with half the channel density to work at 96kHz This method of interfacing between equipment is referred to variously as Two wire or Split96 AES3 Later manufacturers began to implement extended sample rate interfaces by operating an AES3 interface at twice the normal speed This method of interfacing is usually referred to as Double speed or One wire AES3 Direct interconnection of the two interfaces is not possible although the effects of connecting half of
66. to eliminate truncation distortion in A D converters or where digital wordlength is reduced Dither involves adding noise prior to truncation in order to randomize transfer function thresholds and thus linearize the process resulting in analogue like low signal behaviour See also Truncation Noise Shaping Dynamic Range Enhancement A Prism Sound proprietary encoding scheme whereby extended wordlengths can be recorded or transmitted on shorter wordlength media without sacrificing channels Direct Stream Digital a technique wherein digital audio signals are recorded transmitted or processed in an over sampled noise shaped one bit format Jitter on a digital audio interface This might not be problematic until it is sufficiently bad to cause data to be lost on the interface However most A D and D A converters cannot reject interface jitter from their Reference Sync and so the interface jitter survives as sampling jitter at the conversion point resulting in distortion of the converted audio Instability or phase noise in a digital audio interface or in the clock of an A D or D A converter See also Interface Jitter Sampling Jitter See ADAT Multichannel Audio Digital Interface a 56 channel digital audio interface format on coaxial or fibre optic cable complying with the AES10 standard A Prism Sound proprietary encoding scheme whereby extended wordlengths can be recorded or transmitted on shorter wordlengt
67. udio samples are numbers between one and six and we are going to truncate them i e reduce their resolution so that numbers from one to three become zero and those from four to six become one Clearly much information will be lost and all excursions of the signal between one and three and between four and six will not affect the output at all But if we throw a die for each sample add the number of spots to that sample and translate totals of six and below to zero and totals of seven and above to one we have a simple dithering scheme Input samples of three will be more likely to result in outputs of one than will inputs of one The throw of the die is our dither noise Since all the faces of the die have an equal chance of occurring this is known as rectangular probability distribution function RPDF dither which in fact does not produce perfect linearization We actually use triangular probability distribution function TPDF dither which is like throwing two dice with a resultant increase in the probability of medium sized numbers totals of two and twelve occur much less often than seven Prism Media Products Limited 2001 2004 Page 1 28 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 7 3 2 Noise shaping It is possible to reduce the subjective effect of the added dither noise by either using spectrally weighted blue dither noise which is quieter in the more sensitive
68. ut also as the frequency of the converted tone increases So sampling jitter produces distortions which should sound much worse than conventional analogue harmonic distortions since the spurious components appear at aharmonic frequencies High audio frequencies should suffer worse distortion than low frequencies For low frequency jitter the resulting distortion sidebands appear close in frequency to the audio signals which produce them this should mean that they are masked from our hearing by the same phycho acoustic phenomenon upon which are based sub band perceptual coding schemes such as MPEG This is fortunate since it is quite difficult for a PLL to remove jitter to a good degree even at moderate frequencies but for very low frequencies it would be very difficult indeed 7 1 4 Listening experience In practice it seems that the benefits of careful clock design are very apparent in listening tests On the other hand it can sometimes be difficult to expose the shortcomings of converters with poor clocks because these units often have other analogue problems whose severity might obscure jitter related effects In general some of the widely noted effects of sampling jitter are not surprising for example the muddying of brass strings and high frequency percussion and the loss of stereo or multi channel imaging These are well explained by the worse distortions which result in the lab at loud high frequencies and the way th
69. uts Pressing the SOURCE Access button again moves to the next analogue input related Menu and so on in a cyclic fashion When you have found the Menu you want you should be able to alter the desired parameter using the Menu keys in combination with the Channel Select buttons at the bottom of the Meter Panel if the parameter must be altered per channel If you can t find how to access the desired parameters refer to the Firmware Reference If the parameters are obscure you may need to navigate the Menu system manually without the help of the Access buttons Finally you should be able to check the correct operation of the ADA 8XR in system by using the eight bargraph meters on the Meter Panel and perhaps also the two channel Monitor feature which is controlled from the Monitor Panel at the left hand side of the unit Note that both of these Panels are also assignable to either of the two eight channel Paths with their own Path selector buttons Prism Media Products Limited 2001 2004 Page 1 9 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 3 Layout 3 1 Front Panel The front panel of the ADA 8XR contains four divided panels from left to right The Monitor Panel controls and displays all parameters of the two channel Monitor The Mimic Panel controls and displays all parameters of the routing and processing of the two eight channel audio Paths through the ADA 8XR The Meter Panel cont
70. w of flashing exclamation marks are shown at the right hand side of the LCD display when it is in the default level display mode gt Pressing the right Select Change key enters the Warnings screen where all the current warnings are flashed in turn on the bottom line of the LCD To return to the normal Level display press the left Select Change key lt Prism Media Products Limited 2001 2004 Page 1 14 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 5 Control Panel Operation 5 1 Mimic Panel 1 Path 2 10 SYNC SOURCE SAMPLE RATE Local Video 32k x2 WCK DI 44k1 x4 Overkiller AES DI2 48k Analogue 1 2 DI E MR X 16b Flat 16b MRX e DO1 1 l I Spilte 20b 20b SNS 20b e 20b sos I I I DRE 24b Auto 24b o DRE 0 DO2 SOURCE DECODE DITHER ENCODE TT The Mimic panel is the key to understanding and controlling the flow of signals through the ADA 8XR At any one time it shows the flow of signals through one of the ADA 8XR s two Paths from the assigned source ports through any assigned processing functions through to the assigned destination ports The Path selector button in the top left hand corner of the panel assigns its function to either Path 1 or Path 2 Path 1 is usually the A D Path and Path 2 the D A Path in most standard A D D A configurations but this is flexible The remaining controls and i
71. wordlength is implied To add further dither or noise shaping would merely increase the noise floor of the signal without benefit The second situation occurs if the incoming audio data is digital black i e all the audio data bits are zero In this situation it is undesirable to add dither to the outgoing audio since black in black out operation is useful when compiling tracks etc Some older editing systems require black in black out behaviour to recognise track boundaries Note that digital black input is assumed after 10000 consecutive zero samples have been received and is cancelled immediately on receipt of a non zero sample Note that in fact the second situation is really a subset of the first since black audio data has essentially zero bit wordlength The Auto LED is lit when ALL active channels in the Path are in Auto Dither Defeat mode The MR X LED shows that the output port is being encoded using the Prism Sound MR X format which is a word mapping scheme whereby for example a multi channel digital recorder can be used to record longer wordlengths and or higher sample rates than its native format by sacrificing tracks MR X g is the variant of this format for recorders or data channels with a maximum 16 bit wordlength whereas MR Xz is used for 20 bit media where less track sacrificing results The 20b LED shows that MR X2p encoding is taking place whereas the MR X LED without the 20
72. ystem is also contained in the Firmware Reference Pressing one of the numbered store buttons causes the name of that store to be shown in the LCD display along with an invitation to load recall it and that store can then be loaded by a single press of the Enter Accept key The Bank button cycles around the four banks of stores To save overwrite a store with the current settings of the ADA 8XR press the gt key at which point an invitation to save is displayed after which Enter Accept begins the saving sequence of operations which include the opportunity to enter a 16 character name of your choice or to abort the operation A further press of the key presents an invitation to clear erase the selected store If the selected store is already empty only the saving operation is possible It is possible to Reload factory stores as described in the Firmware Reference This causes the ADA 8XR to generate a number of useful default stores based on the I O Modules fitted and store them in certain locations Any manually altered stores held in these locations are then overwritten but all other stores remain intact Prism Media Products Limited 2001 2004 Page 1 22 Prism Sound ADA 8XR Multi channel A D D A Converter Operation Manual Revision 1 00 6 Adjustments and Upgrades The ADA 8XR mainframe has no need for any physical calibrations or jumpers such calibrations as are necessary are mana

Prism Sound ADA-8XR Operation Manual

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