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Operations Manual

AD122-96 MKIII

7

Word Length and Acoustic Bit Correction

The bottom line controls word length and Acoustic Bit Correction™ parameters:

44.1kHz INTERNAL CRYSTAL
20 BIT WL ABC: HPDF

NS2

Setting Word Length:
The selection of word length (16 to 24 bits) sets the digital output word length. The

NI

setting (word

length not indicated) is a 20 bits default setting as per AES/EBU specifications. The

Model AD122-

96

MKIII

utilizes 22 bits for data (bits 23 and 24 contain little sonic information). We recommend a

default word length setting of 22-24 bits. The front panel "20+" lamp indicates when the output
contains 20 or more bits.

Acoustic Bit Correction™ is designed for applications requiring the use of fewer bits. Simple
truncation of lower order bits introduces sonic side effects (distortions and modulation of the noise
floor by the signal). The Acoustic Bit Correction™ feature provides a selection of dither and noise
shaping algorithms. Dither overcomes distortions and noise modulation, but it also raises the noise
floor. The noise shaping algorithms provide an effective means of retaining higher bit content in a
lower bit format (it shifts the noise energy away from hearing sensitive frequency regions to less
sensitive ones). See Appendix I for a complete discussion of Acoustic Bit Correction™.

Dither choices are:

OFF

no dither

HPDF

high pass probability density function

FLAT

recommended for data compression applications

Noise shaping choices are:

NSOFF

no noise shaping

NS1

,

NS2

,

NS3

or

NS4

user selectable noise shaping curves

Test Tone Screen

To generate a test tone, scroll to the test tone screen and set the frequency, amplitude and destination
(let, right or both). The frequency range is from 1Hz to 20kHz in 1 Hz steps. Amplitude range is 0dB
(full scale) to -99dB in 1 dB steps, with an

OFF

setting for "digital black." To change the frequency or

amplitude by large increments, hold down the

UP

or

DOWN

cursor buttons. For small increments,

press the

UP

or

DOWN

cursor buttons repeatedly.

Press

GO

to start the tone (amplitude, frequency and destination settings may be changed during tone

generation). To stop the tone, press

EXIT

twice (returning to the main screen).

Note that the internal tone generation consists of 24 bits of resolution. The word length at the output is
subject to truncation and dither settings.

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Содержание AD122-96 Mark III

Страница 1: ...Quality Analog to Digital Converter Operations Manual Lavry Engineering Inc 945 Hildebrand Lane NE Suite 110 Bainbridge Island WA 98110 206 842 3552 http www lavryengineering com email techsupport lavryengineering com Revision 1 2 March 2005 ...

Страница 2: ...c range without A weighing and a consistent clean performance over the frequency range The much improved clock scheme provides extremely low jitter with both internal and external lock Achieving the state of the art performance required increased usage of power with much of it converted to heat The MKII runs very hot which does reduce its reliability The MKIII is a redesign of the MKII with a stro...

Страница 3: ...jurisdiction LIMITS AND EXCLUSIONS LAVRY ENGINEERING DOES NOT BY VIRTUE OF THIS AGREEMENT OR BY ANY COURSE OF PERFORMANCE COURSE OF DEALING OR USAGE OF TRADE MAKE ANY OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING WITHOUT LIMITATION ANY WARRANTY OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE TITLE OR NONINFRINGEMENT AND ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED LAVRY ENGINEERING EXPR...

Страница 4: ...dio Control Screen 8 Default Parameters Screen 8 Bar Graph Display Screen 9 Warm up and Calibration 10 Hardware Interconnections 11 Maintenance 11 Part II Specifications 12 Appendix I Acoustic Bit Correction 13 Noise Shaping Curves 16 Appendix II AD122 96 MKIII Input Considerations 17 Appendix III AD122 96 MKIII Soft Saturation 19 Appendix IV Viewing Noise Floor on AD122 96 MKIII Display 21 3 ...

Страница 5: ...narrow lock range 48 kHz narrow lock range 40 50 kHz wide lock range 88 2 kHz narrow lock range 96 kHz narrow lock range 88 44 kHz or 96 48 kHz Vernier Transfer Function Correction The exceptional performance of Lavry Engineering s AD122 96 MKIII is due to design innovations in both analog and digital sections The high power consumption of the A D modules using high voltage rails and high current ...

Страница 6: ...N buttons Pressing EXIT again will cause the unit to go to the main screen To Scroll Through Screens If the screen cursor is present you need to remove it by pressing EXIT When the screen cursor is not present the UP DOWN buttons serve to move from screen to screen To Edit Screens Press ENTER to introduce the screen cursor at the first editable location Each additional pressing of ENTER will move ...

Страница 7: ...io data and Word Clock The BNC connector is for Word Clock only as part of the optional IO 96 interface Lock range narrow lock range utilizing VCXO internal voltage controlled crystal oscillators or wide lock range internal low jitter VCO Possible choices for the SYNC WC INPUT XLR connector are XLR AES LOCK 44 1 Phase synchronous XLR AES LOCK 48 0 Phase synchronous XLR AES WIDE LOCK Phase synchron...

Страница 8: ...s provide an effective means of retaining higher bit content in a lower bit format it shifts the noise energy away from hearing sensitive frequency regions to less sensitive ones See Appendix I for a complete discussion of Acoustic Bit Correction Dither choices are OFF no dither HPDF high pass probability density function FLAT recommended for data compression applications Noise shaping choices are...

Страница 9: ...f audio to allow for some settling time less then 3 seconds and to avoid a click sound The algorithm continues to monitor and correct for slow varying offset variations Polarity POLARITY corresponds to analog input signal connection with pin 3 hot POLARITY corresponds to analog input signal connection with pin 2 hot Note that polarity reversal works for both balanced and unbalanced analog input si...

Страница 10: ...oring low level signals such as noise floor requires prior setting of DC removal at the audio control screen DC REMOVAL ON 2 Viewing the noise floor takes some getting used to The display shows a true picture of peak and peak hold information the blinking of LED s is due to low level quantizations Peak readings are at about 11dB higher than the rms noise for flat noise spectrum 3 Measuring the con...

Страница 11: ...s encountered Display contrast The LCD display may be adjusted from 0 to 7 Warm up and Calibration The recommended warm up time is 15 minutes The unit features automatic calibration A complete calibration cycle about 5 seconds in duration is activated at power on A calibration cycle may be done by pressing both the EXIT and GO buttons simultaneously ...

Страница 12: ...ital audio or to a word clock synchronization source The four BNC connectors provide channel one and channel two data word clock out and word clock in They can be used for synchronizing additional converters to each other or an external TTL word clock Maintenance The Model AD122 96 MKIII is an auto calibrating converter requiring no periodic adjustments The unit s reliance on linear power supplies...

Страница 13: ...erroneous results Unconnected high impedance inputs may pick up unwanted signals 2 Care must be exercised when measuring the noise floor The signal applied to the converter must be lower then the noise floor Ordinary relays and switches may leak too much signal and it may be necessary to move a test tone signal to frequency above Nyquist approx 30KHz Output Bits 16 to 24 bits user selectable Total...

Страница 14: ...oise shapers without dither is undesirable so the unit automatically shuts the noise shaper off when dither is off Using dither with or without noise shaping requires user discretion Ideal data transfer and processing should retain long word length A single word length reduction and therefore dithering and noise shaping should take place last Figure 1 shows a 100 dB 1 kHz 24 bit tone truncated to ...

Страница 15: ...nal word length An A B X test at 16 bit level requires a quiet environment and low level loudness audio The listener must resist the temptation to turn the volume up to unreasonable levels The practice of truncating to short word length 8 12 bits should be avoided The ideal noise shaping curve may be irritating at loud levels Lavry Engineering s listening tests were based on test tones and repeati...

Страница 16: ...the presence of all of the odd harmonics created when the truncation process turned the tone into a 1 lsb square wave Figure 8 shows the result of applying additional processing to this signal and truncating the result thereby creating additional distortion components 20 00 2 02k 4 02k 6 02k 8 01k 10 0k 12 0k 14 0k 16 0k 18 0k 20 0k 22 0k 24 0k FREQ Hz 170 0 165 0 160 0 155 0 150 0 145 0 140 0 135...

Страница 17: ... noise Quantization noise is shifted from these areas to high frequencies where the ear is less sensitive Noise shaping curves should be selected based upon listening tests of specific material to be dithered 20 00 2 02k 4 02k 6 01k 8 01k 10 0k 12 0k 14 0k 16 0k 18 0k 20 0k FREQ Hz 160 0 155 0 150 0 145 0 140 0 135 0 130 0 125 0 120 0 115 0 110 0 105 0 100 0 95 00 90 00 85 00 80 00 AMP1 dBFS AUDIO...

Страница 18: ... level itself The source material may have its own noise level but the A D manufacturer is in no position to decide which part of the material is signal and which part is noise Is it undesirable noise or is it the intentional recording of the wind blowing through the trees Thus any signal must be reproduced accurately All we can do and all we should do amounts to avoiding additional A D noise A D ...

Страница 19: ...vailable 0 12 dB of front panel gain adjustment 2 Balanced input with grounded shield The unit handles up to 24dBu of peak signal with available 0 12 dB of front panel gain adjustment 3 Unbalanced input with floating shield The unit handles up to 24dBu of peak signal with available 0 8 dB of front panel gain adjustment 4 Unbalanced input with grounded shield The unit handles up to 24dBu of peak si...

Страница 20: ... transfer functions The plots show input versus output value between 20dBFS and 0dBFS The algorithm for soft saturation is fundamentally different from classical audio compression A compression algorithm provides time varying gain as a function of signal power The gain variations are slowed down attack and decay envelopes to minimize distortions a sudden step in signal gain generates a time decayi...

Страница 21: ...an exponential curve was based on the nature of the distortions crudely speaking less distortion energy at higher harmonics The key to a smooth transition was to make the slopes of the linear and non linear portions are precisely equal to 22 bit accuracy as always such precision is much more apparent to a listener of 16 bit data then to a viewer of 9 bits graph Unlike the analog soft knee the digi...

Страница 22: ...width 05 Computing the mean and standard deviation yields close to perfect results mean and stdev mean gn 0 001 stdev gn 1 001 Gaussian noise energy is measurable via a rms root mean square meter The proper measurement of converter noise should be done using a rms instrument such as Lavry Engineering s Model 3000 Audio Precision test system or others However the known bell shaped curve coupled wit...

Страница 23: ...ckup of non random noise such as power line hum Explanation for the 8dB factor The Gaussian bell shape curve is unbounded Theoretically speaking very high amplitude may occur but very high amplitudes occur very seldom it has been said that waiting a few trillion years may produce a million volt spike Practical observations show that most of the peaks occur within 3 5 times of the standard deviatio...

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