Lexicon Converter User manual

20/20 AD
20 Bit A/D Converter
User Guide

Lexicon
Copyright © 1994 Lexicon Inc.
100 Beaver Street
Waltham MA 02154-8441 USA
617-736-0300
Fax: [phone]
All Rights Reserved
Thispublicationisprotectedbycopyrightandallrightsarereserved.Nopartofit maybereproducedortransmitted
by any means or in any form, without express prior consent in writing from 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 hazard, do not expose the 20/20 AD to rain or moisture.
Thisequipmentgeneratesandusesradiofrequencyenergyandifnotinstalledandusedproperly,thatis,instrict
accordance with the manufacturer's instructions, may cause interference to radio and television reception. It has
been type tested and found to comply with the limits for a Class A computing device in accordance with the
specificationsinSubpartJofPart15ofFCCRules,whicharedesignatedtoprovidereasonableprotectionagainst
such interference in a residential installation. However, there is no guarantee that interference will not occur in a
particular installation. If this equipment does cause interference to radio or television reception, which can be
determinedbyturningtheequipmentOFFandON,theuserisencouragedtotrytocorrecttheinterferencebyone
or more of the following measures:
Reorient the receiving antenna
Relocate the computer with respect to the receiver
Move the computer away from the receiver
Plug the computer into a different outlet so that the computer and receiver are on different
branch circuits.
If necessary, the user should consult the dealer or an experienced radio/television technician for additional
suggestions. The user may find the following booklet prepared by the Federal Communications Commission
helpful: "How to identify and Resolve Radio/TV Interference Problems."
This booklet is available from the U.S. Government Printing Office, Washington, DC 20402, Stock No. 004-000-
00345-4.
Notice
This triangle, which appears on
your component, alerts you to
the presence of uninsulated,
dangerous voltage inside the
enclosure...voltage that may be
sufficient to constitute a risk of
shock.
CAUTION Thistriangle,whichappearson
your component, alerts you to
important operating and main-
tenance instructions in this ac-
companying literature.
RISK OF ELECTRIC SHOCK
DO NOT OPEN
Printed in the United States of America
Lexicon Part # 070-09090 Rev 2

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
intheseinstructionsviolatessafetystandardsofdesignmanufactureandintendeduseoftheinstrument.
Lexicon assumes no liability for the customer's failure to comply with these requirements.
General definitions of safety symbols used on equipment or
in manuals.
Instruction manual symbol: the product
willbe markedwiththissymbolwhenitis
necessary for the user to refer to the
instruction manual in order to protect
against damage to the instrument.
Indicatesdangerousvoltage.(Terminals
fed from the interior by voltage exceed-
ing 1000 volts must be so marked.)
TheWARNINGsigndenotesahazard.It
calls attention to a procedure, practice,
conditionorthelikewhich,ifnotcorrectly
performed or adhered to, could result in
injury or death to personnel.
The CAUTION sign denotes a hazard. It
callsattentiontoanoperatingprocedure,
practice,conditionorthelikewhich,ifnot
correctly performed or adhered to, could
result in damage to or destruction of part
or all of the product.
The NOTE sign denotes important infor-
mation. It calls attention to procedure,
practice, condition or the like which is
essential to highlight.
GROUND THE INSTRUMENT
To minimize shock hazard the instrument chassis and cabi-
net must be connected to an electrical ground. The instru-
ment is equipped with a three-conductor AC power cable.
The power cable must either be plugged into an approved
three-contact electrical outlet or used with a three-contact to
two-contact adapter with the grounding wire (green) firmly
connected to an electrical ground (safety ground) at the
power outlet. The power jack and mating plug of the power
cablemeetInternationalElectrotechnicalCommission(IEC)
safety standards.
DO NOT OPERATE IN AN EXPLOSIVE
ATMOSPHERE
Do not operate the instrument in the presence of flammable
gases or fumes. Operation of any electrical instrument in
such an environment constitutes a definite safety hazard.
KEEP AWAY FROM LIVE CIRCUITS
Operating personnel must not remove instrument covers.
Component replacement and internal adjustments must be
made by qualified maintenance personnel. Do not replace
components with power cable connected. Under certain
conditions, dangerous voltages may exist even with the
power cable removed. To avoid injuries, always disconnect
power and discharge circuits before touching them.
DO NOT SERVICE OR ADJUST ALONE
Donotattemptinternal serviceoradjustmentunlessanother
person, capable of rendering first aid and resuscitation, is
present.
DO NOT SUBSTITUTE PARTS OR MODIFY
INSTRUMENT
Because of the danger of introducing additional hazards, do
not install substitute parts or perform any unauthorized
modification to the instrument.
DANGEROUS PROCEDURE WARNINGS
Warnings, such as the example below, precede potentially
dangerous procedures throughout this manual. Instructions
contained in the warnings must be followed.
Dangerousvoltages,capableofcausingdeath,arepres-
ent in this instrument. Use extreme caution when han-
dling, testing and adjusting.
SAFETY SYMBOLS
WARNING
WARNING
NOTE:
CAUTION
Electrostatic Discharge (ESD) Precautions
The following practices minimize possible damage to ICs
resulting from electrostatic discharge or improper inser-
tion.
• Keep parts in original containers until ready for use.
• Avoid having plastic, vinyl or styrofoam in the work
area.
•. Wear an anti-static wrist-strap.
• Discharge personal static before handling devices.
• Remove and insert boards with care.
• Whenremovingboards,handleonlybynon-conductive
surfaces and never touch open-edge connectors ex-
cept at a static-free workstation.*
• Minimize handling of ICs.
•. Handle each IC by its body.
• Do not slide ICs or boards over any surface.
• Insert ICs with the proper orientation, and watch for
bent pins on ICs.
• Use anti-static containers for handling and transport.
*To make a plastic-laminated workbench anti-static, wash with a solution of Lux liquid
detergent, and allow to dry without rinsing.
CAUTION

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 .....................................................................5
Audio Connections ............................................................................6
Connectors • Cables
Using the 20/20 AD.................................................................................9
Analog Inputs.....................................................................................9
Termination and Grounding via Internal Jumpers .............................9
Balanced and Unbalanced Input Signals.........................................12
Front Panel Adjustments .................................................................13
Synchronization and Sample Rate ..................................................14
AES Sync • Word Clock • Internal and External Modes
About Dither.....................................................................................16
Psychoacoustically Optimized Noise Shaping (PONS)
Automatic Offset Removal...............................................................18
Compressor Modes .........................................................................18
Dynamic Range Compression • Non-Linear Transfer
Functions • Overload Protection • Digitizing Analog Tape
Link • Display
Digital Audio Outputs.......................................................................23
Realigning Two DAT Recordings ....................................................24
Digital Sinewave Generator.............................................................24
Operating the 20/20 AD in the Digitial Mode ...................................25
Specifications.......................................................................................27
Definition of Terms ..............................................................................29

20/20 AD User Guide
Introduction
The 20/20 AD is an analog-to-digital converter which can be configured for
two20-bitchannels,orfour18-bitchannels.Twinon-boardsignalprocessors
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 for more creative
functions, such as emulation of tape saturation or analog compression.
This manual provides some basic information on conversion, but assumes
the user will be familiar with the principles of analog-to-digital conversion, as
well as with the digital audio interface formats output by the 20/20 AD.
Information on specific data which may be required by any target device
should be obtained from the manufacturer.
Lexicon has attempted to provide correct information and functional capability
corresponding to digital audio standards known and available to us at the time of
publication of this document and manufacture of this instrument. As standards
evolve, Lexicon may make updates to documentation and/or system software
available for purchase.
Lexicon'swarrantyonthisproductexcludesconsequentialdamagesresultingfrom
the use of this product. Local jurisdiction may extend the user additional rights.
AES/EBU Interface (Professional)
The AES/EBU interface conforms to both the AES3-1992 (ANSI S4.40-1992) specification and the EBU
document, Tech 3250-E. Both inputs and outputs are balanced, transformer-coupled designs, with a female
XLRinputandamaleXLRoutput,conformingtothestandardconventionofIEC268, Part12.Inputandoutput
levelscomplywithCCITT V.11.Onthisdevice,the professionalformofthe digitalaudioandauxiliarydata has
been labeled "AES" in accordance with general usage.
S/PDIF – Sony/Phillips Digital Interface Format (Consumer)
The S/PDIF interface conforms to the Channel Status Type II format, as specified in the EIAJ CP-340 Digtial
AudioInterface Standard,datedSeptember, 1987,and toIEC 958,FirstEdition 1989-03.As ofNovember 20,
1991, amendments to IEC 958, which include specifications for the implementation of auxiliary data for the
consumer format, were under review. Until new specifications are published, this device must conform to
currentlyapprovedspecifications.Onthisdevice,theconsumerformofthedigitalaudioandauxiliarydatahas
been labeled "SPDIF" in accordance with general usage.

1
Controls and Connectors
20/20 AD User Guide
Afterunpackingthe20/20AD,saveallpackingmaterialsincaseyoueverneed
toshiptheunit.Thoroughlyinspectthe20/20ADandpackingmaterialsforsigns
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
The20/20 AD is equippedwitha 3-pin IEC connectoranddetachableline cord.
Connect the cable end of the 20/20 AD line cord to the 20/20 AD power
connector. Then plug the line cord into an AC wall socket providing voltage
corresponding to the data plate on the unit.
The 20/20 AD measures 19"W x 1.75"H x 13.9"D (483 x 45 x 353 mm). Make
sure that the 20/20 AD is securely screwed into the rack, and that support is
provided for the rear of the chassis during transport to avoid possible damage
from severe mechanical shock.
Themaximumambientoperatingtemperatureis95°F(35°C).Provideadequate
ventilation if the 20/20 AD is mounted in a closed rack with heat-producing
equipment.
Mounting
Unpacking
Power
Controls and
Connectors

Lexicon
2
Controls and Connectors
1dB SCALE
ALT
PK HOLD
ATTEN
1
THRESHUNBAL THRESHUNBAL
2 3
THRESHUNBAL THRESHUNBAL
4
4 CHAN
~EMPH
OVL
0
3
6
12
18
24
30
36
42
60
OVL
0
3
6
12
18
24
30
36
42
60
MUTE
+
•
–
M
C
P
20/20 AD
Front Panel
Controls
The Converter
4 CHAN
Pushon-pushoffselectionof
2-channel or 4-channel
mode; lit when in 4-channel
mode.
EMPH
Turns pre-emphasis on and
off.
Gain Controls: 1, 2, 3 and 4
Provide continuously vari-
ablegaincontrolovera30dB
range.
Note: In 2-channel mode,
only 1 and 2 are active.
UNBAL
Lights when there is a mis-
matchbetweenthe inputsig-
nal and the setting of the
rear-panel Balance switch.*
1dB SCALE
Press to select 1dB Scale
display on level meters.
Also used to select alternate
modes.
PK HOLD
Press to cause the level
meter LEDs to hold at the
highestlevelreceived. Press
again to deactivate.
ATTEN
Press to attenuate balanced
input signals by 6dB. Press
again to turn attenuation off.
Do not use this control on
unbalanced signals.
The 20/20 AD front panel controls are divided into three functional groups for
conversion, compression, and synchronization/output formatting.
THRESH
When the compressor is on,
indicates that the input level
hasrisenabove theselected
compression threshold.
20/20 AD
POWER
20 BIT A/D CONVERTER
1dB SCALE
ALT
PK HOLD
ATTEN
1
THRESHUNBAL THRESHUNBAL
2 3
THRESHUNBAL THRESHUNBAL
4
4 CHAN
~EMPH
OVL
0
3
6
12
18
24
30
36
42
60
OVL
0
3
6
12
18
24
30
36
42
60
DISPLAY
RMT
LINK
ON
6
GAIN
8
10
12
4
2
0
-14
-10
0-36
-18
-22
-26
100
mS
THRESHOLD RELEASE
DITHER
FORMAT
AES / WC:
SAMPLE RATE
EXT SYNC
DIGITAL COMP/LIMITER
-6
                                    
Converter Compressor Synchronization and
Output Formatting
MCP
1S10
0+•–
MUTE
∞
VID
+
•
–
M
C
P
WIDE
HF
48
AES
WC
PRES
20BIT
PL DN
44.1
SPDIF
AES
LOCK
* Non-linearity of the potentiometer can cause the signal to become unbalanced when the level knob is
set to 11:30. To correct this, turn the knob slightly in either direction until the UNBAL light goes out.

3
Controls and Connectors
20/20 AD User Guide
The Level Meters
Whenthecompressoris off ,thebehaviorofthelevelmetersisdeterminedbythesettings
of the 1dB SCALE, and PK HOLD switches.
When the compressor is
on , pressing DISPLAY will cause gain reduction (in dB) to be
displayedonthetworighthandmeters(2-channelmode)oronallfourmeters(4-channel
mode).
The following charts show all of the possible states of the level meter and the value in
decibels for each state.
The Compressor
DISPLAY
Press to cause gain reduc-
tion to be displayed on the
level meters — In 2-channel
mode,onlytherighttwolevel
meters are activated; in 4-
channel mode, all four level
metersdisplay compression.
Press again to deactivate.
GAIN
Adjusts the gain of low level
signals (below the compres-
sion threshold) between the
converter and the compres-
sor.
THRESHOLD
Sets the level at which com-
pression starts.
none
1 dB SCALE
DISPLAY
Normal
1 dB Scale
Gain Reduction
Normal
1 dB Scale
Gain Reduction
none
1 dB SCALE
DISPLAY
Normal
Normal
Normal
(Blank)
1 dB Scale
Gain Reduction
Switches ON Meters 1 & 2 Meters 3 & 4
4-Channel
Mode
2-Channel
Mode
1dB SCALE
GAIN
REDUCTION
NORMAL
OVL
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
1
2
3
4
5
6
7
8
9
10
11
OVL
0
-3
-6
-12
-18
-24
-30
-36
-42
-60
- red -
- red -
- yellow -
- yellow -
- green -
- green -
- green -
- green -
- green -
- green -
- green -
OVL
0
3
6
12
18
24
30
36
42
60
DISPLAY
RMT
LINK
ON
6
GAIN
8
10
12
4
2
0
-14
-10
0-36
-18
-22
-26
100
mS
THRESHOLD RELEASE
DIGITAL COMP/LIMITER
-6
CPM
•–+
0
10
VID ∞
1S
LINK
In 2-channel mode, links the
leftandrightcompressors;in
4-channel mode, where 1,2
and 3,4 are already linked,
this control links the two
pairs.
ON
Turns the compressor on
and off.
RELEASE
This control allows adjust-
ment of the release time of
the compressor. Release
times from 0mS to ∞are
available. The attack time of
the compressor is automati-
cally set as a function of the
signal rise time.

Lexicon
4
Controls and Connectors
Synchronization and
Output Formatting
Alternate Modes
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. When Word
Clockisselectedasanexter-
nal sync source, the AES
ChannelStatusSampleRate
bit will be set to the sample
rate value you have selected
here.
(The PL DN setting of this
switch is reserved for future
enhancements.)
EXT SYNC
This switch allows selection
of: Internal mode (unlit),
Word Clock source, or AES
source. This is for sync
source
only . See ALT-EXT
SYNC below for digital audio
input.
AES/WC
Ininternalsync mode,PRES
indicates that either WC or
AESisavailableattheinputs
as a sync source.
Inexternalsyncmode,PRES
indicates that the
selected
sync source is present at the
input connectors.
DITHER
FORMAT
AES / WC:
SAMPLE RATE
EXT SYNC
WIDE
HF
48
AES
WC
PRES
20 BIT
PL DN
44.1
SPDIF
AES
LOCK
LOCK lights in external sync
mode to indicate the unit has
successfully locked to the in-
coming signal (WC or AES).
DITHER
Selects the type of dither:
wide bandwidth, 20 bit, or
High Frequency .
FORMAT
Selects the format to be
available at the output con-
nectors, AES or S/PDIF.
Note: The format selected
here will be sent to
all out-
puts.
1dB SCALE
ALT
4 CHAN
~
DISPLAY
RMT
LINK
               
press and hold ...then press one of these.
To activate
the alternate modes...
ATTEN
MUTE
ON
VID
Repeat to exit the alternate mode.
DITHER
EXT SYNC
ALT - ATTEN
Mutes the outputs. Note that
thelevelmetersstillwork.To
unmute, hold ALT and press
ATTEN again.
ALT - 4 CHAN
Activates output of a digital
sinewave at the AES ports.
ALT - DISPLAY
Activates remote mode/front
panel lockout. When acti-
vated, the 1dB SCALE and
DISPLAY LEDs flash and
front panel controls are
locked into their current set-
tings. To unlock, hold ALT
and press DISPLAY again.
ALT - LINK
Only active in 4-channel
mode. Activates a short tone
burst. See Realigning Two
DAT Recordings.
ALT - ON
Reserved for future en-
hancements.
ALT - DITHER
Activates psychoacousti-
cally optimized noise shap-
ing. When activated, WIDE,
20BIT and HF will be lighted.
Note that this type of dither
can only be used in 2-chan-
nel mode; activating will dis-
able 4-channel mode and
compressor functions.
ALT - EXT SYNC
Enables the digital audio in-
put.See
Operatingthe 20/20
AD in the Digital Mode.

5
Controls and Connectors
20/20 AD User Guide
PUSH
DO WORD CLOCK
IN
DO
3 + 4 1 + 2 OUT
AES
SYNC
IN
V ~
PUSH 4IN3
UNBAL
BAL
PUSH PUSH 2IN1
UNBAL
BAL
PUSH
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 & 4 and 1 & 2 are identical.
BAL/UNBAL
Push on/push off switch. Set
button to correspond to input
signal type. A mismatch be-
tween the input signal and
the setting of this switch, will
be indicated on the front
panel by the BAL LED.
Analog Input
3-pin XLR connectors. In 2-
channel mode, only inputs 1
and 2 are active.
AC Power
Standard 3-pin IEC power
connector.
Sync/Digital Audio Input
3-pinXLRconnector,professionalformatAES/EBUbalanced
digital input.
75Ω, unbalanced BNC connectors for word clock in/out.
The input and output connectors conform to published stan-
dardsforprofessionalandconsumerformats.The 20/20AD,
however,providestheuser-selectedformatatallconnectors,
e.g. the AES format, if selected, will be available at the
consumer-type outputs, as well as at the XLR outputs.
20/20 AD
Rear Panel
Connectors