Symetrix 402 User manual

402
402 DUAL OUTPUT DELAY
User’s Guide

i
Table of Contents
402
Chapter 1 Introduction 1
Chapter 2 Operator Safety Summary 2
Chapter 3 First time Setup 3
Chapter 4 Front & Rear Panel Overview 4
Chapter 5 BlockDiagram 7
Chapter 6 Operation 8
Chapter 7 Sound System Basics 10
Chapter 8 Connecting to Other Gear 13
Chapter 9 Applications 16
Chapter 10 Troubleshooting 17
Chapter 11 Specifications 19
Chapter 12 Warranty & Service 21
Appendix A Declaration of Conformity 23
Rev B.00, 17 February, 1999
Symetrix part number 53402-0B00
Subject to change without notice.
©1999, Symetrix, Inc. All right reserved.
Symetrix is a registered trademark of Symetrix, Inc.
Mention of third-party products is for informational
purposes only and constitutes neither an endorsement
nor a recommendation. Symetrix assumes no
responsibility with regard to the performance or use
of these products.
Under copyright laws, no part of this manual may be
reproduced or transmitted in any form or by any
means, electronic or mechanical, including photo-
copying, scanning, recording or by any information
storage and retrieval system, without permission, in
writing, from Symetrix, Inc.
14926 35th Ave. West
Lynnwood, WA 98037 USA
Tel [phone]
Fax [phone]
Email [email protected]

402
1
IntroductionChapter 1
The Symetrix 402 is a single-input, dual-output digital delay intended for use in sound systems,
video production, and other applications requiring a high-quality digital signal delay. The 402 uses
oversampling 20-bit A/D and D/A converters to achieve recording-studio signal quality in an
affordablepackage.
Each of the two outputs may be delayed from the input in 1-millisecond steps, up to a maximum
delay of 885 milliseconds (999 feet , 304 meters, or 29 frames). The delay time settings are stored in
nonvolatile memory. A rear-panel switch defeats the front panel delay time switches to prevent
tampering. Each input and output has a level control.
In bypass mode (via the BYPASS switch or during power-off conditions) the inputs and outputs are
hard-wiredtogether.
A 12 segment LED display shows peak input level and is calibrated to assist the user in making the
right trade-off between dynamic range and headroom.
All inputs and outputs are available via XLR connectors, TRS phone jacks, and screw terminals.
We recommend that you read this manual from cover to cover. Somewhere between the confines of
the two covers you should find the answers to most (98%) of your questions, both technical as
well as musical. Should you have any comments or questions, please do not hesitate to contact us
at the numbers/addresses below. Your calls are always welcome.
Phone: [phone]
Fax: [phone]
Email: [email protected]
Website: www.symetrixaudio.com
Front Panel
PIN-1
=LOW(-)
=GND
=HIGH(+)
RING=
TIP=
CONNECTIONS:
SLEEVE=
PIN-3
PIN-2
TYPICAL
INPUT
UNBALANCED/
BALANCED
INPUT
BALANCED
DELAY 2 OUT
DELAY 1 OUTPUT
UNBALANCED
BALANCED
DELAY 2 OUTPUT
MANUFACTURED IN
LYNNWOOD, WA USA
UNBALANCED
BALANCED
LOCKOUT
FRONTPANEL
MAXIMUM
15 WATTS
AC INPUT
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
DELAY 1 OUT
Rear Panel
DELAY SETTINGSOUTPUTS
DUAL OUTPUT
DELAY
402
INPUT
DELAY
INCREASEDECREASE
DELAY
FEET
Msec
FRAMES
DISPLAY UNITS
DELAY
DELAY 1
SELECT
METERS
DELAY 2
DELAY 2
LEVEL
DELAY 1
LEVEL
CLIP-1-2-12 -6 -3
INPUT
LEVEL
SYSTEM
STATUS
-18-24-36 -30-48 -42
IN
BYPASS
HEADROOM

402
2
Operator Safety Summary Chapter 2
Terms
Several notational conventions are used in this
manual. Some paragraphs may use Note, Caution,
or Warning as a heading. Certain typefaces and
capitalization are used to identify certain words.
These are:
Note Identifies information that needs
extra emphasis. A Note generally
supplies extra information to help
you to better use the 402.
Caution Identifiesinformationthat,ifnot
heeded, may cause damage to the
402 or other equipment in your
system.
Warning Identifies information that, if
ignored, may be hazardous to your
health or that of others.
CAPITALS Controls, switches or other markings
on the 402’s chassis.
Boldface Strong emphasis.
Equipment Markings
AVIS:
NE PAS OUVRIR
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
S’adresser a un reparateur compétent.
RISQUE DE CHOC ELECTRIQUE
N
o user serviceable parts inside. Refer servicing to qualified service personnel
.
CAUTION
WARNING:
TO REDUCE THE RISK OF FIRE OR
ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE
DO NOT OPEN
RISK OF ELECTRIC SHOCK
The lightning flash with arrowhead symbol within an
equilateral triangle is intended to alert the user of the
presence of uninsulated “dangerous voltage” within
the product’s enclosure that may be of sufficient
magnitude to constitute a risk of electric shock to
persons. The exclamation point within an equilateral
triangle is intended to alert the user of the presence of
importantoperating andmaintenance (servicing)
instructions in the literature accompanying the
product (i.e. this manual).
Caution To prevent electric shock, do not use the
polarized plug supplied with the unit with
any extension cord, receptacle, or other
outlet unless the blades can be fully
inserted.
ImportantSafetyInstructions
Please read and keep these instructions. Heed
and follow all warnings and instructions.
Install in accordance with the manufacturer’s
instructions.
Power Source This product is intended to
operate from a power source that does not apply
more than 250V rms between the power supply
conductors or between either power supply
conductor and ground. A protective ground
connection, by way of the grounding conductor
in the power cord, is essential for safe operation.
Grounding The chassis of this product is
grounded through the grounding conductor of
the power cord. To avoid electric shock, plug the
power cord into a properly wired receptacle
before making any connections to the product. A
protective ground connection, by way of the
grounding conductor in the power cord, is
essentialforsafeoperation.Donotdefeatthe
safetypurposeofthegroundingplug.The
grounding plug has two blades and a third
grounding prong. The third prong is provided for
your safety. When the provided plug does not fit
your outlet, consult an electrician for replacement
of the obsolete outlet.
DangerfromLossofGround Iftheprotective
ground connection is lost, all accessible conduc-
tive parts, including knobs and controls that may
appear to be insulated, can render an electric
shock.
ProperPowerCord Useonlythepowercord
and connector specified for the product and your
operating locale. Use only a cord that is in good
condition.Protectthepowercordfrombeing
walked on or pinched, particularly at plugs,
convenience receptacles, and the point where
they exit from the apparatus.
Proper Fuse The user accessible fuse is a part of
the IEC AC inlet connector. The fuseholder
accepts5x20mmdiameterfuses.For117VAC
operation,thecorrectvalueis0.2A,250VAC,
slowblowing.For230VACoperation,thecorrect
valueis0.1A,250VAC,slowblowing.
OperatingLocation Donotoperatethisequip-
mentunderanyofthefollowingconditions:
explosive atmospheres, in wet locations, in
inclementweather,improperorunknownAC
mainsvoltage, or if improperly fused.Do not
install near any heat source such as radiators,
heat registers, stoves, or other apparatus
(including amplifiers) that produce heat. Unplug
this apparatus during lightning storms or when
unused for long periods of time.
StayOut oftheBox Toavoidpersonal injury (or
worse), do not remove the product covers or
panels. Do not operate the product without the
covers and panels properly installed. Only use
accessories specified by the manufacturer. Clean
only with a damp cloth.
User-serviceableparts Therearenouser
serviceable parts inside the 402. In case of failure,
refer all servicing to the factory. Servicing is
required when the 402 has been damaged in any
way, such as when a power supply cord or plug
is damaged, liquid has been spilled or objects
have fallen into the apparatus, the apparatus has
been exposed to rain or moisture, does not
operate normally, or has been dropped.

402
3
Fast SetupChapter 3
Follow these instructions to get your 402 up-and-running as quickly as possible.
Connections
Connect your input source to either the XLR, TRS, or barrier strip connections. Connect the 402’s
output to your sound system’s power amplifier inputs using either the XLR, TRS, or barrier strip
connections.
Connect the AC input to an AC power source of the proper voltage and frequency, as marked on
the rear of the unit.
Caution: Failure to connect the 402 to the proper AC mains voltage may cause fire and/
or internal damage. There are no user serviceable parts inside the chassis.
Refer all service to qualified service personnel or to the factory.
Warning: Lethalvoltagesarepresentinsidethechassis.Therearenouserserviceable
partsinsidethechassis.Referallservicetoqualifiedservicepersonnelorto
thefactory.
Settings
Set the controls and switches on the front panel as follows:
IN/BYPASS - IN
INPUT LEVEL - Adjust for signal peaks at -1 dB maximum, as indicated on the Headroom display
formaximumdynamic range.For +4dBu systems,thecorrectsettingismaximumCCWrotation.For
-10 dBu systems, the correct setting is full CW rotation.
DELAY 1 LEVEL - Adjusts Delay 1 output level. For -10 dBu systems, the correct setting is full CCW
rotation. For +4 dBu systems, the correct setting is full CW rotation.
DELAY 2 LEVEL - Adjusts Delay 2 output level. For -10 dBu systems, the correct setting is full CCW
rotation. For +4 dBu systems, the correct setting is full CW rotation.
DELAY SELECT - Your choice.
DISPLAY UNITS -Your choice.
On the rear panel, ensure that the FRONT PANEL LOCKOUT switch is in the OUT position.
Initial Setup
The 402’s controls and switches are now set according to the preceding section. All connections
listed in the “Connections” section are now made. The 402 should now pass signal. The LED
display should be illuminated.
Set the input level by increasing the setting of the input level control until the amber LEDs in the
HEADROOM display illuminate. Ideally, the highest signal level should illuminate the -1 dB LED, and
the CLIPPING LED should never illuminate (the CLIPPING LED operates at clipping. If the CLIPPING LED
illuminates, rest assured that clipping actually occurred).
Set the DELAY 1 and DELAY 2 LEVEL controls by comparing the signal levels between BYPASS and
INand adjusting the control(s) for equal levels. Set the delay time for each output as follows:
1. Depress the DELAY SELECT switch until the delay select LEDs indicate the desired delay.
2. Depress the DISPLAY UNITS switch until the delay units LEDs indicate the desired display
units(milliseconds, feet or meters).
3. Depress the INCREASE or DECREASE switches until the numeric display indicates the desired
amount of delay.
4. Repeat this procedure for the remaining delay output.
Ensure that the output signals are delayed from the input signal (since the 402 will pass signal, albeit
without any delay, even without AC power applied). You can check this by setting the IN/BYPASS switch
to BYPASS. Unless you have selected a very short delay, you should hear a “time-shift” in the program
when you do this. Remember to set the IN/BYPASS switch back to IN. The 402 is ready for use.

402
4
Front & Rear Panel Overview Chapter 4
Input Controls
IN/BYPASS - Enables the 402 when depressed; hard wire bypass when out or during power-off
condition
INPUT LEVEL -Adjustsinputlevelformaximumdynamicrange
INPUT METER - Indicates the input signal level and headroom of the 402. During operation, you
shouldneverseethered(CLIP)LEDilluminate.
OutputControls
DELAY 1 LEVEL - Adjusts output level for Delay
1.
DELAY 2 LEVEL - Adjusts output level for Delay
2.
Mode Controls
DELAY SELECT - Selects delay line whose delay
timeisdisplayedinthenumeric LED display.
DELAY SELECT LEDs - Indicates which delay’s
parameters are being displayed.
DISPLAYUNITS LEDs-TheseLEDsindicate
which delay increment unit is being used for
thenumericLEDdisplay.
DISPLAY UNITS - Pressing this button changes
the units displayed in the numeric LED display
from time to distance units.
INPUT
CLIP-1-2-12 -6 -3
INPUT
LEVEL
SYSTEM
STATUS
-18-24-36 -30-48 -42
IN
BYPASS
HEADROOM
OUTPUTS
DELAY 2
LEVEL
DELAY 1
LEVEL
FEET
Msec
FRAMES
DISPLAY UNITS
DELAY
DELAY 1
SELECT
METERS
DELAY 2

402
5
Power & Serial #
Front Panel Lockout
LEDDISPLAY - Three-digit display indicates delay time for the currently selected delay.
INCREASE - Pressing this button increases the delay time for the current output in 1 ms, 1 foot, 1
meter,or 1 frame steps.
DECREASE - Pressing this button decreases the delay time for the current output in 1 ms, 1 foot, 1 meter,
or 1 frame steps.
ACPOWER INPUT -IEC-power
connector. Connect only to
appropriate AC power source.
Referto rear-panelstickerfor
correct AC source value.
SERIAL NUMBER - Do yourself a
favor and write this number down
somewhere safe, and while you’re
at it, would you please send us the
completedwarranty card?
FRONT PANEL LOCKOUT switch - Push-push
switch disables all front panel switches. The
input and output level controls are not
affected.
DisplayControls
DELAY SETTINGS
DELAY
INCREASEDECREASE
DELAY
MAXIMUM
15 WATTS
AC INPUT
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTO
N
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
MANUFACTURED IN
LYNNWOOD, WA USA
UN
B
LOCKOUT
FRONTPANEL
N.

402
6
INPUTS-TRS(1/4-inchtip-ring-sleeve)
phone,XLR-female. All oftheinputs
arewiredinparallel.
OutputConnectors
OUTPUTS-XLR-male,
balanced; TRS phone,
unbalanced. The
barrier strip output
and the XLR output
arewiredinparallel.
The TRS output jacks
may be strapped for
balanced operation.
Terminal Strip
TERMINAL STRIP -
Barrierstripwith#6
screwterminals.
Contains connections
for all outputs and
inputs (wired in
parallelwiththeir
respective connec-
tors), circuit ground
and chassis ground.
Inputs
DELAY 1 OUTPUT
UNBALANCED
BALANCED
DELAY 2 OUTPUT
UNBALANCED
BALANCED
U
N
B
INPUTDELAY 2 OUT DELAY 1 OUT
PIN-1
=LOW(-)
=GND
=HIGH(+)
RING=
TIP=
CONNECTIONS:
SLEEVE=
PIN-3
PIN-2
TYPICAL
INPUT
UNBALANCED/
BALANCED
BALANCED

402
7
BALANCED/
UNBALANCED
BALANCED
INPUT
INPUT
DECREASE
Msec
METERS
FRAMES FEET
DISPLAY
UNITS
SELECT
DELAY
DELAY
INCREASE
AUDIO
MEMORY
DELAY
STATUS
10 OHM
.1MFD
LINK
SYSTEM
GROUND
DIGITAL
SIGNAL
PROCESSOR
(DSP)
MEMORY
PROGRAM
A/D
CONVERTER
2 CHANNEL
D/A
CONVERTER
LEVEL
INPUT
UNBALANCED
OUTPUT 2
CIRCUIT GROUND - OUTPUT 2 + OUTPUT 2 CIRCUIT GROUND - OUTPUT 1 + OUTPUT 1
UNBALANCED
OUTPUT 1
BALANCED
OUTPUT 2
BALANCED
OUTPUT 1
DELAY 2
LEVEL
DELAY 1
LEVEL
H
E
A
D
R
O
O
M
D
I
S
P
L
A
Y
-48
-42
-36
-30
-24
-16
-12
-6
-3
-2
-1
CLIP
BYPASS
RELAY
BYPASS
RELAY
FRONTPANEL
LOCKOUT
+ INPUT
CHASSIS GROUND
CIRCUIT GROUND
- INPUT
DELAY 1
DELAY 2
DISPLAY AND USER INTERFACE
PRESS
REV-C
Block DiagramChapter 5

402
8
Operation Chapter 6
This section is intended for more advanced users. If you are a first-time 402 user, we recommend
that you start out by using the procedure found in “First Time Setup” (Chapter 3).
Block Diagram
On the preceding page you can find the block diagram for the 402. Please take a moment and make
note of the following:
rBypass mode is a hard-wire bypass for each channel.
rTheTRS,XLR andscrew inputterminals areallparalleled.
rThe XLR and screw output terminals are paralleled.
rThe TRS output jack is wired for unbalanced operation (tip = positive (+), ring and sleeve
grounded).
Installation
The 402 may be installed freestanding or rack mounted. No special ventilation requirements are
necessary.
Mechanical One rack space (1.75 inches) required, 10 inches depth (including connector
allowance). Rear chassis support recommended for road applications.
Electrical 105-125VAC,12.5watts.
Connectors XLR-3female for inputs, XLR-3 maleforoutputs, Pin 2 of theXLRconnectorsis
“Hot.” TRS female and barrier strip connectors are also provided.
Level Setting, Headroom, and Noise
The 402 uses a novel approach to maximizing the overall signal-to-noise ratio at both the inputs
and outputs. If you follow our recommendations, then each block of the 402’s circuitry operates at
its optimum signal level. This is especially important for the digital portions of the 402.
The following table illustrates the concept:
Nominal Input Delay1or
Signal Level Delay 2
Level Control Level
+4dBu(1.23V) Full CCW Full CW
-10dBv(.245V) Full CW FullCCW
If you set the controls as suggested in the table, the 402 will have 18dB of headroom above either
of the nominal signal levels. For optimum signal to noise performance in nominal +4 dBu systems,
you may want to reduce the amount of headroom somewhat. Do this by turning the INPUT LEVEL
control up (clockwise) until you see the desired signal level on the HEADROOM DISPLAY. Then, turn
the OUTPUT LEVEL control down (counterclockwise) by the same amount that you turned the INPUT
LEVEL control up.
Please Note: Thesecontrolsettings represent astartingpoint. You can fine-tune the input level
by using the 402’s LED level display by adjusting the mixer’s output for a 0 VU level signal (or
other suitable reference). Then adjust the INPUT LEVEL control on the front panel so that the display
indicates peaks up to the -1 dB LED. You may want to disconnect the output connections from the
unit when setting the input level.
If you use the output level controls to balance the ratio between your main speaker cluster and the
fill speakers, it is important that you set the gain of the portion of the sound system that follows
the 402 as if the 402 wasn’t there. This ensures that the 402 operates at or near unity gain, which
ensures the best overall signal-to-noise ratio through the 402. You can quickly establish the unity
gain setting by using the bypass switch as a way to compare signal levels.

402
9
DUAL OUTPUT DELAY 402
VIDEO
RECORDER
DIGITAL F/X
SWITCHER
AUDIO
MIXER
AUDIO PATH
VIDEO PATH
VIDEO
PLAYBACK DECK#1
VIDEO PLAYBACK
DECK#2
(ONE PER AUDIO CHANNEL)
Using the Delay Units Mode
The 402 can display its delay time in either units of time (milliseconds) or units of distance (feet or
meters). The 402 converts any settings into an internally used value (the number of samples); thus
the display may appear to be inconsistent (due to internal rounding of fractional values) when
switching back and forth between time units and distance units. The display indicates the time or
distance represented by the internal delay setting, rounded to the nearest whole unit.
Since one foot represents 0.886 milliseconds of delay, this also represents the maximum resolution
of the 402’s delay time setting.
Fine Tuning the Delay Time
Once you’ve established the proper delay setting, it may be necessary to make small adjustments
in the setting. This can actually vary on a day-to-day basis, however most system operators ignore
the day-to-day variation.
The factors that can actually influence the delay time are temperature, humidity, and wind. The
delay time is influenced by temperature and humidity because the speed of sound is temperature
dependent, and the relative humidity affects the density of the air, which affects the speed of
sound. Finally prevailing winds may affect the delay time by causing refraction; effectively
lengthening the path to the listener’s ears.
For the most part, you can ignore the effects of temperature and humidity, except perhaps, in
situations where both occur in the extreme (like inside an ice rink). Remember that the dominant
variable is the distance, and that the listeners sit within a zone, rather than all in the same seat.
Video Post Applications
Insert the 402 in the audio signal path before the recorder. (See diagram below for a typical
hookup.) Use the DISPLAY UNIT button on the front panel to select FRAME delay increments. Adjust
the delay time to account for the amount of frame delay from passes through frame synchronizers,
digital signal processors, time base correctors, or satellite transmission.
This is also a very useful technique in cases where the source tape already has some video delay
due to previous passes through frames synchronizers etc.
Note: The 402’s frame delay feature is based on the NTSC standard 29.97 frames per second. It
willalsoworkfortheHDTV standard 30 frames/sec. However, if you are using PAL (25
frames/sec), set the DISPLAY UNITs to milliseconds and calculate the delay needed based
on40millisecondsperframe.

402
10
Sound System Basics Chapter 7
Providing even coverage under balconies and other architectural features is a common problem in
many auditoriums. At first glance, simply adding fill loudspeakers under the obstruction, directly
connected to the sound system, seems like a reasonable solution. It is, but it works at the expense
of the virtual image of the sound source since the sound from the fill speakers reaches the
listener’s ears much sooner than that emanating from the stage or the stage-mounted loudspeak-
ers.
A further refinement of the solution adds a time delay to the signal sent to the fill loudspeakers.
This delays the arrival of the sound from the fill speakers by an amount of time slightly greater
than that required to travel the distance through air. The figure below illustrates this point. A
psychoacoustical effect restores the illusion of the sound emanating from the source.
REV-A
402 DIGITAL DELAY
DELAYED OUTPUT
REMOTE
STACK
OR ARRAY
PRIMARY
STACK
OR ARRAY
Using time delay to equalize arrival time difference due to different acoustical path lengths.
TheHaasPrecedence Effect
In the late 1940’s, Helmut Haas, a German physicist, published a paper titled, “The Influence of a
Single Echo on the Audibility of Speech.”1The paper explores how our hearing perceives delayed
sound delivered simultaneously with non-delayed sound and how it affects intelligibility. Dr. Haas
describes a variety of tests, taken in a variety of surroundings.
Although Dr. Haas widely receives credit for the precedence effect, examination of the literature shows
that other researchers were studying this phenomenon as early as 18492.
Dr. Haas’ paper states that if two sounds arrive at our ears, within a specific period, the later of the
two sounds may be louder without destroying the localization of the source. What does this mean
for a sound system using fill loudspeakers? If the signal sent to the fill system is delayed suffi-
ciently such that the sound arriving at the listener’s ears is 10-30 milliseconds longer than the
acoustical path delay (distance times the speed of sound) the Haas effect causes the source of the
earlier signal to localize as the apparent source. This is true even if the later (delayed) signal is
significantly (up to about 10 dB) louder than
the early signal. The figure to the left shows
the relationship between the delay and the
level of the secondary source.
1 “The Influence of a Single Echo on the Audibility of
Speech.”, Helmut Haas, Journal of the Audio Engineer-
ing Society, March 1972. Also reprinted in the JAES
anthology: “Sound Reinforcement.” This paper was
originally titled, “ber den EinFluss des Einfachechos
auf die Horsamkeit von Sprache.” It was submitted as a
dissertation toward a doctor’s degree and was later
translated into English and published in the United
States by the AES.
2 See bibliography at the end of this chapter.
Time difference (ms)
Diff
erence
b
e
t
ween
di
rec
t
an
d
delayed signals (dB)
0
2
4
6
8
10
12
14
5 10152025304050
Level difference versus delay for speech

402
11
REV-A
402 DIGITAL DELAY
DELAYED OUTPUT
REMOTE
STACK
OR ARRAY
PRIMARY
STACK
OR ARRAY
T
1
T2
T3 T4
Details
When applying a digital delay such as the 402 in an actual sound system, we must consider the
following acoustical sources of time delay:
1. The source to microphone distance.
2. The source to listener distance.
3. The primary sound system to listener distance.
4. The fill system to listener distance.
In an application where microphones are always close talked (like a rock and roll PA), we can ignore
item 1. In applications where the listener is sufficiently distant or where the acoustical contribution
of the source to the listener is minimal, we can ignore item 2. The figure below illustrates the
relationship between the various sources and the listener.
To calculate the delay needed, you’ll need the following distances:
t1. The source to microphone distance.
t2. The source to listener distance.
t3. The primary sound system to listener distance.
t4. The fill system to listener distance.
Next convert the distances into delay times:
td
c
=where: t= delay (sec) d = distance (ft or m)
c=velocityof sound (1129ft/sec or 344.1m/sec at 71.5F)
The approximate delay needed for the fill speakers will be:
tt t t t
h
=+−+134 where:
t=approximate delayrequired
t1 = source to mic delay
t3 = main system to listener delay
t4 = fill system to listener delay
th=Haasdelay,10-30 ms
The relationship between sources and listener.

402
12
Additional Delay Zones
Some installations require additional delay zones (coverage zones provided by delayed fill loud-
speakers). Begin by establishing the delay required for each zone. Next examine the signals
between adjacent zones and ensure (by varying the delay times) that the arrival times for signals
from overlapping zones fall within the Haas zone. If it is not possible to manipulate the delay times
to guarantee arrival times within 20-30 milliseconds, it may be necessary to alter the coverage of
the adjacent speakers, or to reduce their level slightly. Of course, this is easier to do when you are
working on paper, rather than on the premises.
Other Uses for Delay
Of course, the 402 can also be used where a single or double semi-fixed delay might be needed, for
instance, to provide fixed slapback at two different rates for an effect, or for satellite uplink transit
timecompensation.
Digital delays are also used for speaker cluster alignment, however the 1 ms/1 ft minimum delay
adjustment of the 402 is too coarse for this application.
RelatedReading
If you are interested in conducting further research into the precedence effect or the applications
of time delay in audio systems design, the following list of articles and papers is a good starting
point.
“The Influence of a Single Echo on the Audibility of Speech.”, Helmut Haas, Journal of the Audio
Engineering Society, March 1972. Also reprinted in the JAES anthology: “Sound Reinforcement.”
“ThePrecedenceEffectinSoundLocalization.”HansWallach,EdwinBNewman,MarkR.
Rosenzweig, TheAmericanJournalofPsychology, July 1949. Reprintedin JAES,December1973.
“Sound Reinforcement,” an anthology of articles from the pages of the Journal of the Audio
EngineeringSociety.Copyright1978,AudioEngineeringSocietyInc,NewYork,NY.
“Sound System Engineering”, second edition, Don and Carolyn Davis, Copyright 1987, Howard
W.Sams & Co., Indianapolis IN.
“The Master Handbook of Acoustics,” second edition, F. Alton Everest, Copyright 1989, Tab Books
Inc.,BlueRidgeSummitPA.
“SomeSingle- andMultiple-Source LocalizationEffects,” MarkB. Gardner, JournaloftheAudio
Engineering Society, July/August 1973. Contains extensive bibliography.
“Designing an Auditorium Sound Reinforcement System,” Peter D. Hisocks, Journal of the Audio
EngineeringSociety,December 1973.
“Scientific Writings of Joseph Henry,” Joseph Henry, Smithsonian Institute, Washington, D.C. 1886.
For details of the 1849 date, see footnote at bottom of p. 295.
Although the formula given is quite precise, in practice the actual delay time is not. The actual path
taken by the sound waves varies according to temperature and relative humidity. The dominant
variable in any installation is the distance difference, and although temperature and humidity are
factors, their effect on the overall delay are small compared to the effect of changing the distance.
Thus it will always be necessary to fine-tune the final adjustment either by ear or by using test
equipment.
The 402 makes setting the delay time easy. Start out by selecting the mode corresponding to the
distance units that you use (feet or meters). Select the delay, based on distance, required. Then
switch to time units and add the Haas delay and any additional correction needed. There is more
adjustment resolution when using feet or time mode than when using meters mode.

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Connecting to Other GearChapter 8
This section discusses a multitude of things, all related to getting signals in and out of the 402.
Matching Levels versus Matching Impedances
In any audio equipment application, the question of “matching” inevitably comes up. Without
digging a hole any deeper than absolutely necessary, we offer the following discussion to (hope-
fully) clarify your understanding of the subject.
Over the years, we have all had impedance matching pounded into our heads. This is important
only for ancient audio systems, power amplifiers, and RF. Technically speaking, the reason is
power transfer, which reaches a maximum when source and load are matched. Modern audio
systems are voltage transmission systems and source and load matching is not only unnecessary,
but undesirable as well.
rAncient audio systems operate at 600 ohms (or some other impedance value), and must be
matched, both at their inputs and at their outputs. Generally speaking, if you are dealing with
equipment that uses vacuum tubes, or was designed prior to 1970, you should be concerned about
matching. These units were designed when audio systems were based on maximum power transfer,
hence the need for input/output matching.
rPower amplifiers are fussy because an abnormally low load impedance generally means a
visit to the amp hospital. Thus, it’s important to know what the total impedance of the pile of
speakers connected to the amplifier really is.
rRF systems are matched because we really are concerned with maximum power transfer
and with matching the impedance of the transmission line (keeps nasty things from happening).
Video signals (composite, baseband, or otherwise) should be treated like RF.
Some folks seem to believe that balanced/unbalanced lines and impedances are related; or even
worse that they are associated with a particular type of connector. Not so. Unbalanced signals are
not necessarily high-impedance and balanced signals/lines are not necessarily low-impedance.
Similarly,although 1/4 inch jacks are typically used forthings like guitars (which are high-imped-
ance and unbalanced), this does not predispose them to only this usage. After all, 1/4 inch jacks
are sometimes used for loudspeakers, which are anything but high-impedance. Therefore, the
presence of 3-pin XLR connectors should not be construed to mean that the input or output is low-
impedance (or high-impedance). The same applies to 1/4 inch jacks.
So, what is really important? Signal level, and (to a much lesser degree), the impedance relation
between an output (signal source) and the input that it connects to (signal receiver).
Signal level is very important. Mismatch causes either loss of headroom or loss of signal-to-noise
ratio. Thus, microphone inputs should only see signals originating from a microphone, a direct (DI)
box, or an output designated microphone-level output. Electrically, this is in the range of approxi-
mately -70 to -20 dBm. Line inputs should only see signals in the -10 to +24 dBm/dBu range.
Guitars, high-impedance microphones, and many electronic keyboards do not qualify as line-level
sources.
The impedance relation between outputs and inputs needs to be considered, but only in the
followingway:
Alwaysmakesurethatadevice’sinputimpedanceishigherthantheoutputsourceimpedanceof
thedevicethatdrivesit.
Some manufacturers state a relatively high-impedance figure as the output impedance of their
equipment. What they really mean is that this is the minimum load impedance that they would like
their gear to see. In most cases, seeing a output impedance figure of 10,000 (10K) ohms or higher
from modern equipment that requires power (batteries or AC) is an instance of this type of rating. If
so, then the input impedance of the succeeding input must be equal to or greater than the output
impedance of the driving device.
Symetrix equipment inputs are designed to bridge (be greater than 10 times the actual source
impedance) the output of whatever device drives the input. Symetrix equipment outputs are

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Polarity Convention
The 402 uses the international standard polarity convention of pin 2 hot. Therefore:
XLR Tip-Ring-Sleeve Signal
1 Sleeve Ground
2 Tip High
3 Ring Low
If your system uses balanced inputs and outputs, and uses the 402 this way, then the polarity
convention is unimportant. If your system is both balanced and unbalanced, then you must pay
attention to this, especially when going in and coming out through different connector types (like
input on an XLR, output on a phone jack).
Input and Output Connections
The figure on the next page illustrates how to connect the 402 to balanced and unbalanced sources
and loads.
To operate the 402 from unbalanced sources, run a 2-conductor shielded cable (that’s two conduc-
tors plus the shield) from the source to the 402. At the source, connect the low/minus side to the
shield, these connect to the source’s ground; connect the high/plus side to the source’s signal
connection. At the 402, the high/plus wire connects to pin 2, the low/minus wire connects to pin 3,
designed to drive 600 ohm or higher loads (600 ohm loads are an archaic practice that won’t go
away). You don’t need to terminate the output with a 600 ohm resistor if you aren’t driving a 600
ohm load. If you don’t understand the concept of termination, you probably don’t need to anyway.
The two facts that you need to derive from this discussion are:
1. Match signal levels for best headroom and signal-to-noise ratio.
2. For audio, impedance matching is only needed for antique equipment and power amplifier
outputs. In all other cases, ensure that your inputs bridge (are in the range of 2 to 200
times the output source impedance) your outputs.
Signal Levels
The 402 is designed around studio/professional line levels: +4 dBu or 1.23 volts. The unit is quiet
enough to operate at lower signal levels such as those found in semipro or musical-instrument (MI)
equipment(-10dBuor300millivolts).
I/O Impedances
The 402 is designed to interface into almost any recording studio or sound reinforcement applica-
tion. This includes:
r600 ohm systems where input and output impedances are matched.
rUnbalanced semiprofessional equipment applications.
rModern bridging systems where inputs bridge and outputs are low source impedances
(voltage transmission systems).
The 402’s input impedance is 9400 ohms balanced, and 4700 ohms unbalanced. The inputs may be
driven from any source (balanced or unbalanced) capable of delivering at least -10 dBu into the
aforementioned impedances.
The 402’s output impedance is 100 ohms balanced, 50 ohms unbalanced. The output line driver
delivers +22 dBu into an open-circuit balanced load, or +17 dBm into 600 ohm unbalanced loads,
unbalanced.

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Input and output connector wiring. These diagrams represent the majority of connectors used in modern
audio equipment. Locate the source connector in the left column and match it up with the destination
connector in the right column. Wire your cable according to the diagrams.
FROM UNBALANCED OUT
FROM NON-TRANSFORMER (ELECTRONIC)
BALANCED OUTPUT
(TYPICAL OF SYMETRIX PRODUCTS)
FROM BALANCED OUT
FROM UNBALANCED OUT
FROM BALANCED OUT
FROM BALANCED OUT
FEMALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
MALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
TERMINAL STRIP
(+) = HIGH
(-) = NOT USED
= GROUND
FEMALE XLR
PIN 1 = GROUND + LOW
PIN 2 = HIGH
PIN 3 = NOT USED
2
2
2
3
3
3
1
1
1
RING
RING
SLEEVE
SLEEVE
TO BALANCED IN
TO BALANCED IN
TO UNBALANCED IN
TIP
TIP
TO UNBALANCED IN FROM
TRANSFORMER COUPLED OR
FLOATING BALANCED OUTPUT
TO BALANCED IN
REV-B
and the shield (always) connects to pin 1. This is the preferred method as it makes best use of the
402’s balanced input (even though the source is unbalanced). The other alternative shown
converts the 402’s balanced input into an unbalanced input at the input connector. This works, but
is more susceptible to hum and buzz than the preferred method. There is no level difference
between either method.
You can drive unbalanced loads with the 402’s outputs by using the XLR connector with pin 3 left
open. In an emergency (the show must go on), you can ground pin 3, but if you have the
choice...leave it open. If you must ground pin 3, it is must be grounded at the 402, rather than at the
other end of the cable. The price, regardless of whether or not pin 3 is grounded is 6 dB less output
level. This can be easily made up via the output gain controls.
The 1/4-inch input jack is paralleled with the XLR-input and the screw terminals. In a large installa-
tion, it is permissible to use one of the connectors as the input connection and to use either or
both of the remaining connections for paralleling other inputs with the 402.
The 1/4 inch output jack is a TRS (tip-ring-sleeve) jack wired for unbalanced operations, in parallel
with the terminal strip and XLR output connections. When the 402's output is unbalanced, it's level
willdropby6dB.

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Applications Chapter 9
Here are a few applications that the 402 lends itself to.
Distributed Sound Systems
This is probably the primary use for the 402. As described in the “Sound System Basics” chapter
(Chapter 7), the 402 delays its input signal so that the direct sound from the source and the
amplified sound from the sound system’s fill speakers arrive at the listener’s ears at approximately
the same time (approximately because the sound from the fill system should arrive a bit later than
the direct sound to preserve the illusion of the source). If the primary sound system must be
mounted forward of the stage opening, then the 402 can also be used to delay this system slightly
so that the direct sound from the stage and the amplified sound from the primary sound system
arrivesimultaneously.
RecordingApplications
When recording a live performance, the primary pickup microphone is located some distance away
from the orchestra or group. If you use accent microphones to “sweeten” the sound of a particular
instrument, or if you add the vocal mix for a pop group, often there is enough acoustical delay
between the accent mics and the primary pickup to cause comb filtering or a lack of presence. The
402 can be used to delay the signals from the accent microphone(s) to force them into time coher-
encewith the primarymicrophone(s).
Satellite Transit Time Compensation
Sometimes a simultaneous audio-video feed arrives from the source via two completely different
paths. The visuals may travel via a satellite uplink and downlink while the audio may take a
terrestrial path. When this occurs, the sound and pictures will be out of sync by the difference in
length of the two paths. A geostationary satellite orbits the earth at an altitude of 22,500 miles
whichresultsinanoveralltransittimeof242milliseconds(22500x2/186000).
To compensate for this delay, the 402 can be used to delay the audio signal by an amount equal to
the difference in their paths.
Effects
Although the 402 makes no claim at being a be-all effects box, it can be used to generate two
distinct delays, which might be used for slapback effects. If you return the 402’s outputs via a pair
of input modules on your board, you can also create repeating echo effects by simply sending
some of the 402’s output back to its input. The 402 might be a bit difficult to use in this application
because the user interface wasn’t designed for rapid changes in the delay time. On the other hand,
if you can live with relatively preset delay times and superb audio quality, the 402 will work just
fine, thank you.
Video Post Applications
There are several sources of video frame delay in the video editing process. Whenever you send a
video signal though a frame synchronizer, digital signal processor, or time base corrector, the video
signal will be delayed by one frame. Satellite video transmission can also cause delay problems if the
audio is transmitted separately via land line. In order to keep the video and audio locked together, one
must delay the audio by the same amount that the video has been delayed. Hence the need for the 402
Dualoutput delay, which can display its delay timein milliseconds or NTSC frames.

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Symptom ProbableCause
No output Check cables and connections.
Are inputs driven by outputs, and outputs driving inputs?
Verify cables, source and load by patching input and output
connections together, at the unit.
Check output by plugging headphones into output TRS jacks.
Is the HEADROOM display operating?
Check for AC power presence. Power LED on?
Hum or buzz in output Check input connector wiring.
Ground loop. Check related system equipment grounding. Are
all system components on the same AC ground?
Check grounding options.
Distortion Check input signal. Is it too hot, or is it already distorted?
Is the HEADROOM display indicating clipping?
Check output loading. It should be above 600 ohms.
Arethepoweramplifier(s)clipping?
Is something else clipping?
Noise (hiss) Check input signal levels, and level control settings.
The HEADROOM display should indicate the presence of signal,
up to but not including the CLIP led.
Check gain settings on downstream equipment. The system
gain structure should be such that the 402 operates at or near
unity gain.
Is the input signal already noisy?
NoLEDdisplay Is the unit plugged in, and turned on?
Is the AC outlet OK?.
Nodelay Is the unit in BYPASS mode?
Is the unit plugged in? (The unit reverts to BYPASS when power
is disconnected!)
No nothing Is the unit turned on?
TroubleshootingChapter 10

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