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Summary of Contents for Lexicon Converter
- Page 1 User Guide 20/20 AD 20 Bit A/D Converter...
- Page 2 This publication is protected by copyright and all rights are reserved. No part of it may be reproduced or transmitted by any means or in any form, without express prior consent in writing from Lexicon. Lexicon Part # 070-09090 Rev 2...
- Page 3 Failure to comply with these precautions, or with specific warnings elsewhere in these instructions violates safety standards of design manufacture and intended use of the instrument. Lexicon assumes no liability for the customer's failure to comply with these requirements. GROUND THE INSTRUMENT To minimize shock hazard the instrument chassis and cabi- net must be connected to an electrical ground.
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Page 4: Table Of Contents
Controls and Connectors ... 1 Unpacking • Power • Mounting ... 1 Front Panel Controls ... 2 The Converter • The Level Meters • The Compressor Synchronization and Output Formatting • Alternate Modes Rear Panel Connectors ... 5 Audio Connections ... 6 Connectors •... -
Page 5: Introduction
20/20 AD User Guide The 20/20 AD is an analog-to-digital converter which can be configured for two 20-bit channels, or four 18-bit channels. Twin on-board signal processors provide 20-bit to 16-bit compression in the digital domain, as well as DC removal and a choice of four dither types. -
Page 6: Controls And Connectors
20/20 AD User Guide After unpacking the 20/20 AD, save all packing materials in case you ever need to ship the unit. Thoroughly inspect the 20/20 AD and packing materials for signs of damage. Report any shipment damage to the carrier at once. The following accessories are included with the 20/20 AD: 1. -
Page 7: Front Panel Controls
4 CHAN Push on-push off selection of THRESH 2-channel or 4-channel 4 CHAN mode; lit when in 4-channel EMPH mode. EMPH Turns pre-emphasis on and off. Lexicon POWER 20/20 AD 20 BIT A/D CONVERTER... -
Page 8: The Level Meters
In 2-channel mode, links the signals (below the compres- left and right compressors ; in sion threshold) between the 4-channel mode, where 1,2 converter and the compres- and 3,4 are already linked, sor. this control links the two pairs. Turns the compressor on and off. - Page 9 ALT - LINK Only active in 4-channel mode. Activates a short tone burst. See Realigning Two DAT Recordings. Lexicon SAMPLE RATE Selects the sample rate of the A/D conversion. This switch should be set to the same sample rate as your sync source.
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Page 10: Rear Panel Connectors
20/20 AD User Guide AC Power Standard 3-pin IEC power connector. 3 + 4 Digital Output Two 3-pin XLR connectors, professional format AES bal- anced digital outputs. Two consumer format optical (fiber-optic) outputs. Two consumer format unbalanced coaxial RCA outputs. Note: In 2-channel mode 3 &... -
Page 11: Audio Connections
XLR Pinout — pin 2 high by convention Description Balanced RS-422 Balanced RS-422 Unbalanced 75 Consumer Digital Unbalanced 75 pin 2 high 2 = high Male 3 = low 1 = ground 1 = ground 3 = low 2 = high Lexicon... - Page 12 20/20 AD User Guide This interface requires balanced connections using high-quality, low-capaci- tance, controlled-impedance, data communication, twisted-shielded pair cable. Microphone cable may introduce a significant amount of jitter into the signal, causing distortion. Use commercially-available, consumer audio optical cable assemblies. This interface is unbalanced but, because it carries digital signals, it requires the use of 75 RG-59 coaxial cable.
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Page 13: Using The 20/20 Ad
20/20 AD User Guide The 20/20 AD has four analog inputs: CH1, CH2, CH3 and CH4. In two-channel mode, only CH1 and CH2 are used, and the dynamic range of the unit is extended. If you have two stereo pairs, one of which is used more often than the other, the most often used pair should be assigned to CH1 and CH2, and the other pair to CH3 and CH4. -
Page 14: Jumper Settings
20/20 AD is shipped from the factory. CHASSIS GROUND 600 OHM W17 110 OHM 75 OHM CONNECTOR AES OUT TWISTED PAIR CONNECTOR S/PDIF OUT 75 OHM COAXIAL CHASSIS CONNECTED TO EARTH GROUND THROUGH POWER CABLE OR GROUND STRAP Lexicon SHIELDED... - Page 15 20/20 AD User Guide The following figure indicates the locations and factory settings of these jumpers on the board. In their closed positions, the jumpers have their right two (or lower two) pins shunted together. To open a jumper, move the shunting block to the left (or upper) two pins.
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Page 16: Balanced And Unbalanced Input Signals
Set the pot so that it is in the middle of the range where the UNBAL light is out. e) Remove the pot and measure the resistance. Solder a resistor of that value between the correct pin and ground. Lexicon... -
Page 17: Front Panel Adjustments
DIGITAL COMP/LIMITER section is set to OFF. In normal operation, each level meter will indicate the level at the output of the converter in dB referenced to digital full scale (dBfs). A lighted green or yellow LED indicates that the signal has exceeded the level printed next to it. -
Page 18: Synchronization And Sample Rate
Word Clock. This will add jitter to the sample rate, which will, in turn, add noise and distortion to the analog/ digital converter. Refer to Page 7 for recommended cables. The WORD CLOCK OUT signal is a logic-level square wave at the sample frequency. - Page 19 20/20 AD User Guide The 20/20 AD is shipped configured for Internal mode. To operate in External mode, press EXT SYNC until the desired sync source (WC or AES) lights. If the selected sync source light flashes and the PRES light is not on, it indicates that there is no signal present as a sync source.
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Page 20: About Dither
Using the 20/20 AD Lexicon Dither is a low-level pseudo-random signal which is added to digital audio to About Dither reduce quantization noise, in effect, by replacing it with a “nicer sounding” noise. If the recorder or workstation which follows the 20/20 AD is capable of recording or processing 20 bits, the DITHER switch should be set to 20 BIT. - Page 21 20/20 AD User Guide -60.00 -70.00 -80.00 -90.00 -100.0 -110.0 -120.0 -130.0 -140.0 -150.0 -160.0 2.00k 4.00k 6.00k 8.00k 10.0k 12.0k Plot of noise + distortion vs. frequency for the 20/20 AD in 2- channel mode with a -60dBfs sinewave at 1kHz. -60.00 -70.00 -80.00...
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Page 22: Automatic Offset Removal
With the compressor on, set compressor GAIN to 6dB. This will increase the gain of low level signals (below the THRESHOLD setting) by 6dB, effectively squeezing the dynamic range of the converter in 2-channel mode from 110dB to 104dB. The DITHER switch automatically adds just enough dither to squeeze... - Page 23 (GAIN settings above 12dB are not available because at that point practically all of the dynamic range of the converter will fit onto 16-bit media. ) Set THRESHOLD to -24dB. Now, when the signal level exceeds -24dB, the gain is gradually reduced until, at 0dB signal level, the compression gain is also at 0dB (unity).
- Page 24 2.00:1 1.50:1 1.60:1 1.71:1 1.84:1 1.44:1 1.52:1 1.62:1 1.73:1 1.36:1 1.42:1 1.50:1 1.57:1 1.28:1 1.33:1 1.38:1 1.44:1 THRESHOLD RELEASE (in dB) (in mS and S) Lexicon 4.00:1 4.00:1 4.00:1 4.00:1 4.00:1 4.00:1 4.00:1 3.00:1 2.50:1 2.20:1 2.00:1 1.85:1 1.66:1 1.50:1...
- Page 25 20/20 AD User Guide When RELEASE is set to 0, the compressor acts like an amplifier with a non- linear transfer function. For example, setting GAIN to 6dB and THRESHOLD to -14dB produces a close approximation of a generic tape saturation curve. This mode is also useful for overload protection of some types of percussive instruments.
- Page 26 THRESHOLD setting until the clipped signal sounds acceptable. Note: The compressor can only prevent clipping if the analog/digital converter does not overload. Any signal which overloads the converter will also overload the compressor. Although the compressor works in both 4-channel and 2-channel mode, the...
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Page 27: Digital Audio Outputs
20/20 AD User Guide In 2-channel mode, when the LINK switch is off, each of the two channels is compressed independently. When the LINK switch is on, the louder of the two channels sets the amount of compression. This serves the same function as “stereo link”... -
Page 28: Realigning Two Dat Recordings
ALT—4-CHAN may invoke undocumented diagnostics routines. If you accidentally get into diagnostics mode, the best way to exit is to turn the power off, then on again. 5062.5 6937.5 9000 11062.5 14062.5 17062.5 20062.5 (THRESHOLD) Level in dBfs 4651 6374 8269 10163.5 12920 15676 18432.5 Lexicon... -
Page 29: Operating The 20/20 Ad In The Digitial Mode
20/20 AD User Guide The 20/20 AD's Digital Input mode can be used to make use of the digital compressor, or to noise shape the dither spectra before recording 20-bit source material to a 16-bit recording device*. In Digital Input Mode, format in = format out. No format conversion is possible, and the front panel format indicator and selector are disabled. -
Page 30: Specifications
Inputs and Outputs AES, S/PDIF: XLR, 3-wire balanced RCA, 2-wire unbalanced coaxial line Optical, optical fiber Word Clock: BNC, 75 , unbalanced Front Panel Controls Converter Gain (4) 1dB SCALE/ALT PK HOLD ATTEN/MUTE 4 CHAN/~ EMPH DISPLAY/RMT LINK/ tone burst... -
Page 31: Definition Of Terms
AES : Audio Engineering Society. aliasing : a form of distortion which occurs when an A/D converter’s sample rate is less than twice the highest fre- quency component of a signal. amplitude : the maximum departure of the value of a wave- form from its average value.
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