Lexicon 20-20 AD User Manual

20/20 AD

20 Bit A/D Converter

User Guide

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.

Notice

This equipment generates and uses radio frequency energy and if not installed and used properly, that is, in strict
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
specifications in Subpart J of Part 15 of FCC Rules, which are designated to provide reasonable protection against
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
determined by turning the equipment OFF and ON, the user is encouraged to try to correct the interference by one
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. 004-000­00345-4.

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

RISK OF ELECTRIC SHOCK

DO NOT OPEN

This triangle, which appears on
your component, alerts you to
important operating and main­tenance instructions in this ac­companying literature.

Copyright © 1992 Lexicon Inc.

3 Oak Park
Bedford, MA 01730
Tel: [phone]

Fax: [phone]
All Rights Reserved
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

Printed in the United States of America

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.

GROUND THE INSTRUMENT

To minimize shock hazard the instrument chassis and cabi­net must be connected to an electrical ground. The instru­ment 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
cable meet International Electrotechnical Commission (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

Do not attempt internal service or adjustment unless another
person, capable of rendering first aid and resuscitation, is
present.

General definitions of safety symbols used on equipment or
in manuals.

Instruction manual symbol: the product
will be marked with this symbol when it is
necessary for the user to refer to the
instruction manual in order to protect
against damage to the instrument.

Indicates dangerous voltage. (Terminals
fed from the interior by voltage exceed­ing 1000 volts must be so marked.)

The WARNING sign denotes a hazard. It

WARNING

CAUTION

NOTE:

calls attention to a procedure, practice,
condition or the like which, if not correctly
performed or adhered to, could result in
injury or death to personnel.

The CAUTION sign denotes a hazard. It
calls attention to an operating procedure,
practice, condition or the like which, if not
correctly performed or adhered to, could
result in damage to or destruction of part
or all of the product.

The NOTE sign denotes important infor­mation. It calls attention to procedure,
practice, condition or the like which is
essential to highlight.

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.

WARNING

Dangerous voltages, capable of causing death, are pres­ent in this instrument. Use extreme caution when han­dling, testing and adjusting.

SAFETY SYMBOLS

CAUTION

Electrostatic Discharge (ESD) Precautions

The following practices minimize possible damage to ICs
resulting from electrostatic discharge or improper inser­tion.

• 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.

• When removing boards, handle only by non-conductive
surfaces and never touch open-edge connectors ex­cept 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.

20/20 AD User Guide

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

Contents

Specifications.......................................................................................25

Definition of Terms ..............................................................................27

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.

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.

Introduction

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's warranty on this product excludes consequential damages resulting from
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
XLR input and a male XLR output, conforming to the standard convention of IEC 268, Part 12. Input and output
levels comply with CCITT V.11. On this device, the professional form of the digital audio and auxiliary data 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
Audio Interface Standard, dated September, 1987, and to IEC 958, First Edition 1989-03. As of November 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
currently approved specifications. On this device, the consumer form of the digital audio and auxiliary data has
been labeled "SPDIF" in accordance with general usage.

20/20 AD User Guide

Controls and

Controls and Connectors

Connectors

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. 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.
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.

Unpacking

Power

Mounting

The maximum ambient operating temperature is 95°F (35°C). Provide adequate
ventilation if the 20/20 AD is mounted in a closed rack with heat-producing
equipment.

1

Controls and Connectors

20/20 AD

Front Panel

Controls















THRESHUNBAL THRESHUNBAL

OVL

0
3
6
12
18
24
30
36
42
60

1

The 20/20 AD front panel controls are divided into three functional groups for
conversion, compression, and synchronization/output formatting.

Converter Compressor







1dB SCALE

ALT

PK HOLD

ATTEN

MUTE

2 3







THRESHUNBAL THRESHUNBAL







OVL

0
3
6
12
18
24
30
36

M

+

42

C

•

60

P

–







4 CHAN

~

EMPH

4



RMT

VID



DISPLAY

LINK

ON









DIGITAL COMP/LIMITER

6

4

8

10

2

12

0

M

P

C

GAIN









100
mS

-14

-18

-10

-22

-6

-26

THRESHOLD RELEASE

0

+•–

0-36

Synchronization and

Output Formatting



1S10

∞



DITHER

FORMAT

AES / WC:





WIDE

HF
48

AES

WC

PRES







20BIT
PL DN

SAMPLE RATE

44.1

SPDIF

EXT SYNC

AES

LOCK

Lexicon



POWER

20/20 AD

20 BIT A/D CONVERTER

The Converter

THRESHUNBAL THRESHUNBAL

1

1dB SCALE

Press to select 1dB Scale
display on level meters.

Also used to select alternate
modes.

OVL

0
3

6
12
18
24
30
36
42
60

Gain Controls: 1, 2, 3 and 4

Provide continuously vari­able gain control over a 30dB
range.

Note: In 2-channel mode,
only 1 and 2 are active.

1dB SCALE

ALT

PK HOLD

ATTEN

MUTE

2 3

THRESHUNBAL THRESHUNBAL

M
C
P

PK HOLD

Press to cause the level
meter LEDs to hold at the
highest level received. Press
again to deactivate.

UNBAL

Lights when there is a mis­match between the input sig­nal and the setting of the
rear-panel Balance switch.

OVL

0
3

6
12
18
24
30
36

+

42

•

60

–

4

~

4 CHAN

EMPH

ATTEN

Press to attenuate balanced
input signals by 6dB. Press
again to turn attenuation off.
Do not use this control on
unbalanced signals.

THRESH

When the compressor is on,
indicates that the input level
has risen above the selected
compression threshold.

4 CHAN

Push on-push off selection of
2-channel or 4-channel
mode; lit when in 4-channel
mode.

EMPH

Turns pre-emphasis on and
off.

2

20/20 AD User Guide

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

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

, pressing DISPLAY will cause

gain reduction (in dB)

to be

on

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.

Switches ON Meters 1 & 2 Meters 3 & 4

4-Channel

Mode

2-Channel

Mode

none

1 dB SCALE

DISPLAY

none

1 dB SCALE

DISPLAY

Normal

1 dB Scale

Gain Reduction

Normal
Normal
Normal

Normal

1 dB Scale

Gain Reduction

(Blank)

1 dB Scale

Gain Reduction

DISPLAY

Press to cause gain reduc­tion to be displayed on the
level meters — In 2-channel
mode, only the right two level
meters are activated; in 4­channel mode, all four level
meters display compression.
Press again to deactivate.

LINK

In 2-channel mode, links the
left and right compressors ; 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.

DISPLAY

RMT

VID

LINK

ON

4

2

0

GAIN

GAIN

Adjusts the gain of low level
signals (below the compres­sion threshold) between the
converter and the compres­sor.

DIGITAL COMP/LIMITER

6

8

10

12

PM

C

-14

-18

-22

-26
0-36

THRESHOLD RELEASE

THRESHOLD

Sets the level at which com­pression starts.

The Compressor

100

-10

-6

mS

10

0

1S

∞

–+

•

RELEASE

This control allows adjust­ment of the release time of
the compressor. Release
times from 0mS to ∞ are
available. The attack time of
the compressor is automati­cally set as a function of the
signal rise time.

3

Controls and Connectors

Synchronization

Output Formatting

Lexicon

and

DITHER

Selects the type of dither:
wide bandwidth, 20 bit, or
High Frequency .

FORMAT

Selects the format to be
available at the output con­nectors, AES or S/PDIF.

Note: The format selected

all

here will be sent to
puts.

out-

Alternate Modes

DITHER

FORMAT

AES / WC:

AES/WC

In internal sync mode, PRES
indicates that
AES is available at the inputs
as a sync source.

In external sync mode, PRES
indicates that the
sync source is present at the
input connectors.

either

WIDE

HF

48

AES

WC

PRES

WC

or

selected

20 BIT
PL DN

SAMPLE RATE

44.1

SPDIF

AES

LOCK

EXT SYNC

LOCK lights in external sync
mode to indicate the unit has
successfully locked to the in­coming signal (WC or AES).

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
Clock is selected as an exter­nal sync source, the AES
Channel Status Sample Rate
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.

ALT - ATTEN

Mutes the outputs. Note that
the level meters still work. To
unmute, hold ALT and press
ATTEN again.

ALT - 4 CHAN

Activates output of a digital
sinewave at the AES ports.

4

To activate
the alternate modes...

press and hold ...then press one of these.





1dB SCALE

ALT







MUTE



ATTEN

4 CHAN











DISPLAY

RMT



LINK





~

ON

Repeat to exit the alternate mode.

ALT - DISPLAY

Activates remote mode/front
panel lockout. When acti­vated, the 1dB SCALE and
DISPLAY LEDs flash and
front panel controls are
locked into their current set­tings. To unlock, hold ALT
and press DISPLAY again.

VID

ALT - LINK

Only active in 4-channel
mode. Activates a short tone
burst. See

DAT Recordings.

ALT - ON

Reserved for future en­hancements.

Realigning Two





DITHER

ALT - DITHER

Activates psychoacousti­cally optimized noise shap­ing. When activated, WIDE,
20BIT and HF will be lighted.

Note that this type of dither
can only be used in 2-chan­nel mode; activating will dis­able 4-channel mode and
compressor functions.

20/20 AD User Guide

AC Power

Standard 3-pin IEC power
connector.

Analog Input

3-pin XLR connectors. In 2­channel mode, only inputs 1
and 2 are active.

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 be­tween the input signal and
the setting of this switch, will
be indicated on the front
panel by the BAL LED.

3 + 4 1 + 2

DO

V ~

DO

PUSH

Digital Output

Two 3-pin XLR connectors, professional format AES bal­anced 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.

The input and output connectors conform to published stan­dards for professional and consumer formats. The 20/20 AD,
however, provides the user-selected format at all connectors,
e.g. the AES format, if selected, will be available at the
consumer-type outputs, as well as at the XLR outputs.

AES

SYNC

IN

WORD CLOCK
IN

OUT

PUSH

4IN3

UNBAL

BAL

PUSH PUSH

2IN1

UNBAL

BAL

PUSH

Sync Input

3-pin XLR connector, professional format AES/EBU balanced
digital input.

75Ω, unbalanced BNC connectors for word clock in/out.

5