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User Guide
20/20 AD
20 Bit A/D Converter
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Lexicon Precautions The 20/20 AD is a rugged device with extensive electronic protection. However, you should observe the same reasonable precautions that apply to any piece of audio equipment: • Always use the correct line voltage. • Do not install the 20/20 AD in a closed, unventilated rack, or directly above heat-producing equipment such as power amplifiers. • Never attach audio power amplifier outputs (speaker outputs) directly to any of the 20/20 AD's connectors. • To prevent fire or shock
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20/20 AD User Guide SAFETY SUMMARY The following general safety precautions must be observed during all phases of operation, service and repair of this instrument. 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. General definitions of safety symbols used on equipment or GR
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20/20 AD User Guide Contents Introduction 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 .............................................
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20/20 AD User Guide Introduction 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. The compressor allows leeway in setting levels and provides insurance against clipping in the digital domain. In addition, it provides 195 soft compression curves and 13 time constants to allow fo
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Controls and 20/20 AD User Guide Controls and Connectors Connectors After unpacking the 20/20 AD, save all packing materials in case you ever need Unpacking 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. Power Cable 2. User Guide 3. Quick Reference Guide The 20/20 AD is equipped with a 3-pin IEC connector and detachable line cord. Power Con
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Controls and Connectors Lexicon 20/20 AD Front Panel Controls The 20/20 AD front panel controls are divided into three functional groups for conversion, compression, and synchronization/output formatting. Synchronization and Output Formatting Converter Compressor UNBAL THRESH UNBAL THRESH UNBAL THRESH UNBAL THRESH OVL OVL POWER DIGITAL COMP/LIMITER 1dB SCALE DISPLAY DITHER WIDE 20BIT 0 0 100 3 ALT 3 RMT 6 mS -18 -14 HF
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20/20 AD User Guide Controls and Connectors The Level Meters When the compressor is off, the behavior of the level meters is determined by the settings of the 1dB SCALE, and PK HOLD switches. When the compressor is on, pressing DISPLAY will cause gain reduction (in dB) to be displayed on the two right hand meters (2-channel mode) or on all four meters (4-channel mode). The following charts show all of the possible states of the level meter and the value in decibels for each state. GAIN Switche
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Controls and Connectors Lexicon Synchronization and Output Formatting DITHER SAMPLE RATE Selects the type of dither: Selects the sample rate of DITHER WIDE 20 BIT wide bandwidth, 20 bit, or the A/D conversion. This HF PL DN SAMPLE RATE High Frequency . switch should be set to the 48 44.1 FORMAT same sample rate as your AES SPDIF FORMAT EXT SYNC sync source. When Word WC AES Selects the format to be Clock is selected as an exter- AES / WC: PRES LOCK available at th
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20/20 AD User Guide Controls and Connectors 20/20 AD Rear Panel Connectors BAL/UNBAL Push on/push off switch. Set button to correspond to input signal type. A mismatch be- tween the input signal and Analog Input the setting of this switch, will AC Power 3-pin XLR connectors. In 2- be indicated on the front Standard 3-pin IEC power channel mode, only inputs 1 panel by the BAL LED. connector. and 2 are active. 3 + 4 1 + 2 4IN 3 2IN 1 PUSH WORD CLOCK PUSH PUSH PUSH PUSH DO DO IN OUT UNBAL UNBAL
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Controls and Connectors Lexicon Audio Connections Connectors Signal Mating Connector Description AES/EBU XLR A3M Balanced RS-422 Digital Input AES/EBU XLR A3F Balanced RS-422 Digital Output S/PDIF RCA Unbalanced 75Ω Consumer Digital Output S/PDIF Consumer Digital Consumer Digital Audio Optical Output Word Clock BNC Unbalanced 75Ω Analog Input XLR pin 2 high XLR Pinout 2 = high Male 3 = low 1 = ground Female 1 = ground 3 = low 2 = high XLR Pinout — pin 2 high by convention 6
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20/20 AD User Guide Controls and Connectors Cables This interface requires balanced connections using high-quality, low-capaci- AES/EBU tance, controlled-impedance, data communication, twisted-shielded pair cable. Digital Output Microphone cable may introduce a significant amount of jitter into the signal, causing distortion. Use commercially-available, consumer audio optical cable assemblies. S/PDIF Consumer Digital Audio Output Word Clock I/O This interface is unbalanced but, because it carrie
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20/20 AD User Guide Using the 20-/20 AD Using the 20/20 AD The 20/20 AD has four analog inputs: CH1, CH2, CH3 and CH4. In two-channel Analog Inputs 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. This allows you to take advantage of the extended dynamic range of two-channel mode when using only
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Using the 20/20 AD Lexicon CAUTION These instructions are for use by qualified personnel only. Before opening the 20/20 AD, REMOVE THE POWER CORD. You may be exposed to hazardous voltages even if power to the unit is turned off. WARNING Turn off power and REMOVE THE POWER CORD before opening the unit. Take a moment to study the figure below. This diagram shows the terminating and grounding of input signals for the unit, and explains the function of most of the jumpers on the 20/20 AD Main pc boa
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20/20 AD User Guide Using the 20/20 AD 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. (Note that the jumpers in J13 have only two pins; to open, simply remove the shunting block.) W1 W2 W9 W10 W11 W12 W13 W14 Analog Jumpers W17 W27 U30 U31 W18 W16 W26 U42 U48 U49 J13 Digital
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Using the 20/20 AD Lexicon Balanced and Make sure the BALANCE switches located on the rear panel are set to match the type of input. (OUT=balanced , IN=unbalanced). The red UNBAL lights on Unbalanced the front panel will indicate an error if there is a mismatch between the switch Input Signals setting and the signal type. Note that when an UNBAL light goes on, there is a good chance that the input signal has been audibly clipped, even if the level meter does not indicate an overload. If it is ne
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20/20 AD User Guide Using the 20/20 AD Adjust the front panel Gain knobs until the peak input levels are balanced and Front panel come within a few dB of clipping. For now, make sure that the DISPLAY switch Adjustments in the 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 ne
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Using the 20/20 AD Lexicon Synchronization The 20/20 AD can synchronize to its internally derived sample clock at 44.1kHz or 48kHz, or to an external AES or Word Clock signal, in the range of 41-51kHz. and Sample Rate The EXT SYNC switch allows you to select external Word Clock (WC), external AES (AES), or internal source (WC and AES off). Before switching between Internal and External modes, be sure to reduce monitor volume as some D/A converters do not mute when they lose lock. AES Sync The A
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20/20 AD User Guide Using the 20/20 AD Internal and The 20/20 AD is shipped configured for Internal mode. To operate in External External modes 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. If the selected sync source and PRES lights are on, but the LOCK light is off, the selected sync source is present, but is not within the 41-51kHz loc
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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. If, however, the equipment can only record or process a 16-bit signal, either WIDE or HF dither should be selected. This is true even if the compress
