Symetrix 628 Digital Voice Processor User Manual

628 Digital Voice Processor

User’s Guide

628

Table of Contents

Chapter 1 Introduction 1
Chapter 2 Operator Safety Summary 2
Chapter 3 Product Tour and Operations Guide 3
Chapter 4 Audio Processing Basics 14
Chapter 5 Solutions to Possible Problems 20
Chapter 6 Repair and Warranty Information 23
Chapter 7 Symetrix Limited Warranty 24
Chapter 8 Specifications 25
Chapter 9 Architect’s and Engineering Specifications 26
Appendix A Symetrix 628 Factory Presets 27
Appendix B Symetrix 628 Preset Worksheet 28
Appendix C Output Level Conversion 29
Appendix D RC-1 Remote Control 31
Appendix E Input/Output Connections 34
Appendix F Declaration of Conformity 35

Rev B.01, October 7, 1999
Symetrix part number: 53628-0B01
Subject to change at our whim and fancy 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 photo­copying, scanning, recording or by any information
storage and retrieval system, without permission, in

628

writing, from Symetrix, Inc.

Email: [e-mail]

Lynnwood, WA 98037 USA

14926 35th Ave. West

Tel [phone]

Fax [phone]

i

IntroductionChapter 1

Development of the Symetrix 628 grew from requests
by users of our 528 and 528E Voice Processors.
Many were frustrated that their 528 required tweaks
of the processing parameters with each change in
vocalist or broadcaster. Otherwise, they were forced
to compromise their microphone processing by
adopting a “one size fits all” approach with a single
set of processing settings. Most users needed an
affordable, easy-to-use, voice processor which
allowed the creation and recall of a set of processing
parameters for individual users. We responded with
a digital version of the 528E - the Symetrix 628 Digital
Voice Processor.

Use your new 628 with any professional low­impedance, balanced microphone. The 628 powers
balanced, phantom-powered microphones via an
integral phantom supply. The input circuit uses
matched resistors to attain a high common-mode
rejection ratio (CMMR), and multistage filters
prevent RFI problems. A front panel MIC/LINE
switch selects between the microphone input and
line input. The GAIN control adjusts both micro­phone and line input signals.

The input stage feeds a 20 bit A/D converter, then a
24 bit Motorola digital signal processor takes over to
handle the signal dynamics. The 628’s De-Esser
compresses undesirable high-frequency sounds
above the user-selected threshold. The De-esser
attacks only excess sibilance sounds.

RATIO and RELEASE controls on the 628’s discrete
EXPANDER/GATE section offer infinitely more
adjustment range than the 528 or 528E. On the
analog units, the EXPANDER is limited to a single
THRESHOLD control in the COMPRESSOR stage.
The 628’s RATIO control varies function of the
stage between expansion and gating. The 628’s
RELEASE control selects the speed at which the
EXPANDER/GATE operates.

The 628’s COMPRESSOR stage offers improvement
over earlier models with the addition of a RELEASE

control. We retained the familiar THRESHOLD and
RATIO controls. Separate LED meters for both the
COMPRESSOR and EXPANDER/GATE stages
provide visual indication of the amount of process­ing taking place in each section.

The 628 bundles all three parametric equalizers into a
single control area. A push button switch toggles
between LOW, MID and HIGH frequency sections.
The equalizer bands and controls remain the same as
on the 528E, except you now read FREQUENCY,
BANDWIDTH and CUT or BOOST on the numeric
display.

The OUTPUT LEVEL pot tweaks the output gain
and the LED headroom meter provides a visual
indication of the output level. The 628 steps through
its 128 presets with a twist of the PRESET NUMBER
control. Load the indicated preset by pushing the
LOAD button. You save changes to a preset by
pushing the SAVE button.

The 628 provides both analog and digital outputs.
The analog output can be at line level (+4 dBu) or
switched to microphone level (-40 dBu) via internal
jumpers. The digital output supports both AES/EBU
and S/P DIF formats at sample rates of 32 kHz, 44.1
kHz and 48 kHz.

Sounds easy doesn’t it? We don’t make you step
through multilayer menus. The 628 purposely looks
and feels like the 528E; we traded out the analog pots
for binary switches. When you need to make a
change just grab the right knob and give it a turn!

The 628’s front panel is very intuitive; you probably
feel that you don’t need to finish reading the manual.
Don’t cheat yourself, read the manual, learn the finer
points of operating the 628, and get the maximum
benefit from your new 628 Digital Voice Processor.
Call us with any questions or if you have something
tasty on the stove to share (we’ll eat anything but
anchovies).

PRE-AMP

MIC

628

DIGITAL VOICE
PROCESSOR

LINE

-15 PAD
NORM

-12

PHANTOM

CLIP

-18

-15 -9

-6

ACTIVE-3 -12 -18 -15 -6 -9 -3 ACTIVE -9 -15 -18 -12 -3 -6 ACTIVE

75

15

+20-12

FREQUENCY

GAIN
(dB)

THRESHOLD

(kHz)

(dBFS)

THRESHOLD

(dBFS)

RATIO

(X:1)

RELEASE

(Sec)

THRESHOLD

(dBFS)

Front panel

AC INPUT
15 WATTS
MAXIMUM

DIGITAL VOICE

628

PROCESSOR

MANUFACTURED IN LYNNWOOD, WA, USA

FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.

RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.

MIDI

PROGRAM

DUMP SELECT

MIDI

CHANNEL

12

11
10
9
8

7

6

13

5

REMOTE CONTROL

14

15

16

1

2

3

4

MIDI OUT/THRU

MIDI/RC-1 IN

Rear panel

COMPRESSOREXPANDER/GATEDE-ESSER

RELEASE

RATIO

(Sec)

(X:1)

DIGITAL OUTPUT

SELECT

S/P DIF
AES/EBU

AES/EBU

PARAMETRIC EQ

FREQUENCY

(kHz)

SAMPLE

SELECT

48kHz

44.1kHz
32kHz

S/P DIF ANALOG RIGHT

CUT/BOOST

BANDWIDTH

OUTPUT

RATE

UNBALANCED

HIGHMIDLOW

OUTPUT

LEVEL

(dB)(Oct)

UNBALANCED

HEADROOM (dB)

MASTER

4(680-20kHZ)(20-500Hz) (160-6300Hz) ACTIVE 2028 24 1216 8 CLIP

PRESET
NUMBER

SAVELOAD

INPUT

PHANTOM

POWER

ON
OFF

MICROPHONEANALOG LEFT LINE

628

1

Operator Safety Summary Chapter 2

N

.

The information in this summary is intended
for persons who operate the equipment as well
as repair personnel. Specific warnings and
cautions are found throughout this manual
wherever they may apply; they do not appear
in this summary.

The notational conventions used in this
manual and on the equipment itself are
described in the following paragraphs.

Equipment Markings

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

TO REDUCE THE RISK OF FIRE OR

WARNING:

SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.

o user serviceable parts inside. Refer servicing to qualified service personnel

Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.

The lightning flash with arrowhead symbol
within an equilateral triangle is intended to alert
the user of the presence of un-insulated
"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 important operating and mainte­nance (servicing) instructions in the literature
accompanying the 628 (i.e. this manual).

Caution: To prevent electric shock, do not

ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE

RISQUE DE CHOC ELECTRIQUE

AVIS:

NE PAS OUVRIR

S’adresser a un reparateur compétent.

use the polarized plug supplied
with the 628 with any extension
cord, receptacle, or other outlet
unless the blades can be fully
inserted.

Terms

Several notational conventions are used in this
manual. Some paragraphs may use Note,
Caution, or Warning as a heading or certain
typefaces and capitalization are used to
identify certain words. These are:

Note Identifies information that needs

extra emphasis. A Note generally

628

supplies extra information to
help you to better use the 628.

Caution Identifies information that, if not

heeded, may cause damage to
the 628 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 628’s chassis.

Boldface Strong emphasis.

Power source - Electrical power require-

ments for US and Canadian models are 117
VAC Nominal, 105 to 125 VAC, 60 Hz, 20
Watts maximum. UL and C-UL listing applies
only to this rating. This product is intended to
operate from a power source that does not
apply more than 255Vrms 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.

Danger from loss of ground - If the protec­tive ground connection is lost, all accessible
conductive parts, including knobs and controls
that may appear to be insulated, can render an
electric shock.

Proper power cord - Use only the power
supply specified for the product. Use only a
power supply that is in good condition.

Operating location - This product is intended
for use in a rack-mounted environment. Do
not operate this equipment under any of the
following conditions: explosive atmospheres,
in wet locations, in inclement weather,
improper or unknown AC mains voltage, or if
improperly fused.

Stay out of the box - To avoid personal injury
or injury to others, do not remove the product
covers or panels. Do not operate the product
without the covers and panels properly
installed.

Warning: To prevent hazard
or damage, ensure that only

microphone cables and
microphones designed in

compliance with IEC-268­15A are connected.

2

Chapter 3

This chapter provides an overview of the connectors and controls on the 628. We’ll explain the
operation of each as we go along. Please read through this chapter completely first and then refer
to it when necessary as you make connections to the 628 and begin operating the unit.

Product Tour and Operations Guide

Now that you’ve ripped open the box ...

Start by mounting the 628 in your equipment rack with #10-32 screws (not provided). Use plastic or
nylon washers (also not provided) to minimize markings to the front panel. The 628 requires no
special ventilation; just don’t mount it directly over heat generating devices (such as your 200 watt
per channel power amp or your pizza oven). We’ll start around back.

628

MANUFACTURED IN LYNNWOOD, WA, USA

AC INPUT

15 WATTS

MAXIMUM

C

FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.

RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.

Plug the EIN power cord supplied with the 628 into the mains connector on the rear of the unit.
While you’re there, verify that the voltage specification on the 628 matches your local mains
voltage. Look for the voltage specification on the adhesive tag to the right of the power
connector. Check that the plug matches your mains receptacle.

Warning: If the voltage specified does not match your local mains voltage, or if
the plug on the power cord is not correct for your mains receptacle, STOP! Call the
Symetrix dealer (or your country’s distributor) who supplied your unit and trade the
628 for a unit built for your mains voltage.

If everything looks consistent, you may plug the 628 into a mains receptacle. Please verify that
the plug fits all the way into the receptacle so that none of the blades are exposed. Once con­nected to mains power, the 628 will power up. There is no ON/OFF power switch on the 628.

Warning: The 628 is intended to be electrically grounded. It is supplied with a
three-wire grounding plug which has a grounding pin. This plug will fit only a
grounded AC outlet. This is a safety feature. If you are unable to insert the plug into
the outlet, contact a licensed electrician to replace the outlet with a properly
grounded outlet. Do not defeat the purpose of the grounding plug with an adapter.

AUDIO EQUIP. 2T38

DIGITAL VOICE
PROCESSOR

LISTED

813 COMMERCIAL

Connecting with your microphone ...

Next connect your microphone cable
to the 3 pin, female XLR connector on
the far right side of the rear panel, as
viewed from the rear of the 628. The
628 wants to see an output from a
balanced, low-impedance professional
microphone. If the connector on your
microphone connector does not
match the MICROPHONE INPUT
connector of the 628 have a qualified
technician replace the cable connector with a 3 pin, male XLR connector.

Caution: Large transients (loud “pops” and “whoomphs”) may be induced when plugging and

unplugging the microphone connector. Transients also occur when you connect power to
the 628. If you have connected the output of the 628 to a console input or other audio

LINE

INPUT

PHANTOM

POWER

ON
OFF

MICROPHONE

628

3

device, please turn down the fader, or input gain control, to protect your equipment from
any transients.

Note: We wired the microphone input with Pin #2 high (+), Pin #3 low (-) and Pin #1

ground or shield.

Warning: To prevent hazard or damage, ensure that only microphone cables and
microphones designed in compliance with IEC-268-15A are connected.

If your microphone is a dynamic type, leave the PHANTOM POWER switch in the OFF position
(out). Switch the PHANTOM POWER to the ON position (in) when using a condenser micro­phone. Please consult your microphone manual if you don’t know which type of you have. The
front panel PHANTOM LED will light when the phantom voltage is switched on.

Caution: Large transients (loud “pops” and “whoomphs”) will be generated when

turning the phantom power on and off. If you have connected the output of the

628 to a console input or other audio device, please turn down the fader, or
input gain control, to protect your equipment from any transients.

Connecting to a line level audio source ...

When you plan to use the 628 with a line level audio source connection may be made to either the
3 pin, female XLR connector or the 1/4 inch TRS jack. Pin #2 is high (+) on the XLR; tip is high (+)
on the TRS jack. The 628 will accept a line level signal up to +22 dBu at the LINE INPUT connec­tors. You may connect either a balanced or unbalanced circuit to the 628’s input. It is OK to plug
a TS (tip & sleeve) plug into the TRS (tip, ring & sleeve) input jack. Use the GAIN control to
adjust the line level input signal.

Caution: The 628 accepts analog inputs only. There is no provision for a digital input

signal.

Warning: Do not connect the line input of the 628 directly to a telephone line. Use a
telephone coupler or telephone hybrid for interfacing with a telephone line.

Locate the MIC/LINE switch on the far left side of the 628 front panel. When using a microphone
as the audio source, make sure that the button is pushed in. If you wish to use your line level
audio source, push the MIC/LINE switch to the out position.

You can’t have it both ways ...

The 628 allows you to use either the microphone input or the line input,
but not both simultaneously. When you select the “MIC” position, the
628 disconnects the line level input. If you select the “LINE” input the
microphone preamp is disconnected from the input circuit. This keeps
residual noise to a minimum.

Too hot?

Directly below the MIC/LINE switch is the switch for a 15 dB PAD (a
fixed attenuator). You will want this switch in the NORM (normal)
position for most microphones. If you know that your condenser
microphone has an unusually high output, change the pad switch to the
15 PAD position (push-button in).

PRE-AMP

MIC

LINE

-15 PAD
NORM

CLIP

15

PHANTOM

+20-12

GAIN

(dB)

75

Caution: If you notice the CLIP LED flashing while you use the 628 and you have the

628

4

GAIN attenuator at a 9:00 o’clock position or lower, you should engage the 15
dB PAD. The input circuit will also clip if a line level audio source is connected
to the MICROPHONE INPUT connector.

Gain adjustment ...

The remaining task in setting up your 628 input signal is adjustment of the input GAIN attenuator.
This sets up proper gain structure through the 628’s A/D converter. First set the push buttons of
the De-esser, Expander/Gate, Compressor and Parametric EQ to the bypass position. All of the
ACTIVE LEDs will be off. Turn the OUTPUT LEVEL until “0” (unity gain) shows on the MASTER
display below the LED headroom display on the right side of the 628.

While speaking into the microphone in your best “announcer voice”, or while feeding the 628 line
level audio, adjust the input GAIN attenuator until the LED headroom display peaks at an average
of -8 dBfs. All of the green LEDs and the first yellow LED will light. It’s OK if the second yellow
LED (-4 dBfs) flashes on occasional loud peaks.

Take care not to clip the input preamplifier. Check this by using your loudest normal voice when
setting the input GAIN attenuator. We found that a knob position of 12 o'clock is about right for
dynamic microphones. Too much gain applied in the preamplifier also adds unnecessary noise in
the signal path.

Note: The 628’s GAIN control adjusts either the microphone preamplifier gain or the

line input level depending on which input is selected.

Where’s the VU meter?

What’s this “headroom meter” stuff? The analog 528 and 528E use an LED VU meter. There is no
"0" on the 628's meter. When 528s and 528Es hit “0 dB” on the analog meter, the output is 0 dBm
(+4 dBu). The output of these analog processors is referenced to 600 milliwatts into a 600 ohm
load.

Digital audio equipment references signal levels to the clip point. With digital equipment, there is
no “0 dBm” reference point. A signal passing through the 628 at a level of -4 dBfs (dB full scale) is
4 dB below clipping, NOT at -4dBu. The 628 clips at +22 dBu. This means that the -4 dBfs signal
equates to +18 dBu (4 dB below +22 dBu).

The THRESHOLD controls and metering in the Compressor, Downward Expander and De-esser
sections of the 628 are also referenced to the clip point (0 dBfs). When a threshold is set for -10.0
dB, it is set at 10 dBu below clipping, or at a value of +12 dBu.

Let’s compare the difference between a VU meter and a headroom meter with the speedometer in
your car. Your speedometer is like a VU meter. When you travel at 55 m.p.h. (the legal speed limit,
in this example), the speedometer reads “55.” 55 m.p.h. is an absolute speed just as 0 dBm is an
absolute voltage. If you travel at 45 m.p.h., your analog speedometer would read 45 m.p.h..

A “headroom” speedometer would express the speed limit (55 m.p.h.) as “0 m.p.h..” If you travel at
45 m.p.h., the headroom speedometer would display “-10 m.p.h..” The “headroom” speedometer
tells you that you are traveling at a speed 10 m.p.h. below the legal limit. You could speed up
another 10 m.p.h. before getting “clipped” by the cops.

You always want to drive close to the speed limit on the freeway, and the input of digital audio
equipment should be operated as close to the clip point of the A/D converter as possible. This
assures the best resolution of the digital signal. A signal passing through the 628 which registers

-4 dBfs on the headroom meter produces 20-bit audio. A signal passing through with peaks of only

-20 dBfs renders only 14-bit audio. Best digital resolution and optimum signal-to-noise perfor­mance dictates that you keep audio passing through the 628 as high as possible on the headroom
meter.

Let’s move around back again and connect the 628 output.

628

5

SAMPLE

OUTP

U

SELECT

48kHz

S/P DIF
AES/EBU

44.1kHz
32kHz

S/P DIF

RATE

AES/EBU

SELECT

DIGITAL OUTPUT

Under normal circumstances ...

If you plan to use the balanced, line level (+4 dBu) output, the job is easy. Plug a properly wired 3
pin, female XLR connector into one of the analog output connectors. Pin #2 is high (+), pin #3 is
low (-) and pin #1 is circuit ground.
You will notice that we provided
two outputs, ANALOG LEFT and
ANALOG RIGHT. You may use
either, or both.

When you need an analog
unbalanced line level output,
please use one, or both, of the 1/4
inch TS (Tip/Sleeve) jacks. The tip
is high (+); sleeve is ground (-).

The analog output of the 628 may seem higher than the output of your 528 or 528E. You’re right!
Because we want to operate digital circuits closer to the clip point, the analog output signal will
also operate closer to its clip point. If this presents a problem by overloading your console input,
turn down the input trimmer for that channel. If your console does not provide an input trimmer,
insert a fixed pad between the analog output of the 628 and your console input. You may also load
the output of the 628 with a 620 ohm resistor when connecting it to a balanced, bridging input.
Connect the resistor across the high (+) and low (-) connections at the console input.

Note: You may be tempted to simply turn down the OUTPUT LEVEL control on the

628. This is a digital gain control. Remember that digital devices perform
better when operated close to their clip point.

PUTS

UNBALANCED

ANALOG LEFT

UNBALANCED

ANALOG RIGHT

But, I need a mic level output ...

We recommend that you use a line level analog output whenever possible. But, in the real world,
things aren’t always this neat. Some consoles only allow microphone level (-50 dBu) inputs for the
channels providing microphone functions (such as speaker muting or on-air light switching).
Please call your console manufacturer and complain loudly about their lack of flexibility. Any
“quality” console input should provide switching between microphone and line level.

Don’t expect much help from the console guys. That’s OK; we built a solution into the 628. When
backed against the wall, you may convert one, or both, XLR analog outputs of the 628 to micro­phone level output.

Warning: This change is accomplished inside the box via jumpers and must be made by a

qualified electronic technician. A technician can find instructions for this procedure
in Appendix C of this manual. You may return your 628 to us for conversion if you do
not have a qualified technician available. Please call our Customer Service Depart­ment for a return authorization number.

And, I want the digital output ...

Making use of the 628’s digital output requires a few more steps. First determine the sample rate
which you need to feed to your digital input. Move the SAMPLE RATE SELECT toggle switch to
the proper sample rate setting. You must use
sample rates of 48 kHz, 44.1 kHz or 32 kHz.
The 628 makes no provision for synchroniza­tion to an external clock.

The DIGITAL OUTPUT SELECT switch
activates one of the two digital outputs. The
AES/EBU output appears on the 3 pin, male

628

XLR connector. The Sony/Phillips Digital
Interface (S/P DIF) output is on the RCA pin

6

connector. The 628 provides signal to only one digital output format at a time.
As you switch between AES/EBU and S/P DIF, the MASTER display on the front panel will reflect

the change. When you select AES/EBU the display will read "PrO", indicating "professional". If
you use the S/P DIF format, the MASTER display will read "COn", reflecting the "consumer"
format.

Remote control & MIDI ...

If you are not using the Symetrix RC-1 remote control, you can sit out this section. If you have the
RC-1, plug one end of the 7 pin
DIN cable (supplied with the
RC-1) into the MIDI/RC-1 IN
connector. Plug the other end
of the cable into the RC-1
Remote Control. Make sure that
the MIDI CHANNEL SELECT
rotary switch identifies the 628
as Channel #1. Read the
channel number on the switch
or on the MASTER display as
you turn the MIDI CHANNEL
SELECT switch.

DIGITAL VOICE
PROCESSOR

OD, WA, USA

ISTED

MMERCIAL

EQUIP. 2T38

CHANNEL 1

DUMP

SELECT

MIDIMIDI

CHANNELPROGRAM

SELECT

13

12

11

10
9

8

7

6

REMOTE CONTROL

14

15

16

1

2

3

4

MIDI OUT/THRU

5

MIDI/RC-1 IN

Note: You will find

further informa­tion on the RC-1,
including instruction
on how to change the
RC-1’s MIDI channel
identification, in
Appendix D at the rear
of this manual.

With the Symetrix RC-1 connected to the 628 you can select and load any of the first eleven presets
stored in your 628 by pushing the corresponding button on the RC-1. The BYPASS button loads
program #0 which remains a dedicated bypass function and may not be programmed.

When you first connect the RC-1, none of the LEDs will light. Push the button for preset #1. The
LED next to the Program 1 button will light. The MASTER display on the 628's front panel should
display "1", indicating that the command from he RC-1 was received and preset #1 was loaded.

The LEDs on the RC-1 do not provided positive confirmation of which preset is selected on the

628. They simply serve as reminders of which program selection was last sent to the 628. If a
program selection change is made at the front panel PRESET NUMBER knob, the LEDs on the RC-1
will not reflect the change. When in doubt, check the 628's MASTER display, or push the desired
preset button on the RC-1 even though it may already be lighted.

The Symetrix RC-1 cannot make changes to any individual operating parameter on the 628. It
selects and loads presets #0 through #11 only. There is no button lockout or other security feature
provided on the RC-1. If you accidentally hit one of the buttons, you will accidentally change the
processing preset on the 628.

S D.C.

LARITY

RING -

MIDI OUT

POWER IN FROM

SYMETRIX 628

Caution: The Symetrix RC-1 includes a jack for an optional 9 VDC power supply (not sup

plied). If you use the RC-1 with the 628, the RC-1 takes its power from the 628. No
external power supply is required when using the RC-1 with the 628. The optional
9VDC connection allows you to use the RC-1 with MIDI controlled devices (like the
Symetrix 601 and 602).

628

7

Those of you using other MIDI control devices with the 628 will know what to do with the MIDI IN
jack, the MIDI OUT/THRU jack and the MIDI CHANNEL SELECT switch. You’ll find instruction
in the manual which came with your MIDI controller.

Copying programs between units with MIDI ...

Here’s a neat MIDI trick for users of multiple 628s who want all of their units programmed alike.
You can set all programs and parameters manually or you can use MIDI to copy all programs from
one 628 to another. You will need a standard MIDI cable, or 5 pin DIN cable, connected between
the MIDI OUT/THRU connector of your programmed unit (master) and the MIDI/IN connector of
the unit which you want to program (slave). Both units must be on and the MIDI CHANNEL
SELECT switches must be in the Channel #1 position. Push the MIDI PROGRAM DUMP button
on the programmed unit (master). All programs will be downloaded to the slave unit. You can now
disconnect the MIDI cable from the two 628s.

Preset selection ...

Selecting a processing preset on the 628 is very simple. The MASTER numeric display normally
shows the preset currently in use. To change to a different preset, turn the PRESET NUMBER
knob until the
desired preset
number appears
in the window.
The preset
number will
flash indicating
that it has been
selected but not
yet loaded.
Push the LOAD
button to the
right of the PRESET NUMBER knob. Now the window will display the preset number without
flashing, indicating that the 628 has loaded the new preset.

OUTPUT

LEVEL

HEADROOM (dB)

MASTER

42028 24 1216 8 CLIP

SAVELOAD

PRESET

NUMBER

When you unpack your 628, you will find programs 1 through 119 blank. We shipped your 628
with the parameters at these presets set for unity gain with no processing. You will find the pre­programmed factory presets at positions 120 through 127. We programmed these as “read only”
programs; they cannot be changed. You may move them to more convenient locations and then
make any required changes. Here’s how:

Moving a preset program ...

Should you need to copy an existing preset program to a different preset number, you will need to
learn about the SAVE button. This function instructs the 628 to save changes to the selected
preset. First, select and load the program which you want to copy. Second, turn the PRESET
NUMBER knob until the MASTER display shows the location where you wish to copy the loaded
program; the display will flash the number. Third, push the SAVE button; the MASTER display
will show the flashing letters "Sto" (Store). Push the SAVE button again and the 628 will copy the
selected preset program to the new location.

Until you press the SAVE button the second time the preset program will not be copied tot he new
location. This gives you a second chance in the event that the SAVE button is accidently pushed
in the heat of processing. The first push of the SAVE button arms the 628 to make a change and
displays "Sto" in the MASTER display window. The second push permanently records the
change.

Note: Do not try to use the RC-1 Remote Control to select the target location where you want to

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copy the preset program. Pushing a button on the RC-1 accomplishes TWO functions.

8

This operation SELECTS and LOADS the preset. When you copy a preset to another
location, you want to SELECT the target location then SAVE the preset which you wish to
copy at the new location.

You will find the 628's "bypass" preset at program "0". The MASTER display will show the letters
"byP" when you dial it in. You may also load the bypass program from the RC-1 Remote Control.
The bypass button is in the lower right corner (Program 0).

The bypass preset comes in handy when you need to erase a program preset from the 628. Let's
say that you want to delete preset #5. First select and load the bypass preset. Next, rotate the
PROGRAM SELECT knob until the MASTER display reads "5". Push the SAVE button. The
MASTER display will read "Sto". Push the SAVE button again. You have now copied the bypass
settings (no processing and flat EQ) into the processing preset #5. You may now start fresh with a
clean slate and build a new processing preset from scratch at preset #5.

Note: You can find a description of the factory presets and their program numbers in Appendix A.

The Equalizer ...

Since no one remains content to use a standard “factory preset”, you need to know how to modify
presets and create your own programs from scratch. We’ll start with the parametric equalizer
section, since EQ is the first thing
which you will want to tweak for
each individual voice.

The 628 provides three overlapping
bands of parametric equalization with
adjustable frequency and bandwidth.
Operating a parametric equalizer is
like opening a safe; you must dial in
the correct three numbers to properly
accomplish the job.

FREQUENCY

(kHz)

PARAMETRIC EQ

(680-20kHZ)(20-500Hz) (160-6300Hz) ACTIVE

BANDWIDTH

HIGHMIDLOW

CUT/BOOST

(dB)(Oct)

First, make sure that the equalizer is active. Momentarily push the Operate/Bypass button, and the
ACTIVE LED in the PARAMETRIC EQ section will come on. Next, use the Band Select push­button (left of the FREQUENCY knob) to toggle between LOW, MID and HIGH until the band
which you want to adjust is selected.

The first parameter to adjust is the frequency. This selects the center frequency of equalization cut
or boost. Turn the FREQUENCY knob slowly until you feel one click. Notice that the MASTER
numeric display changes to show the frequency (in kHz) currently selected. You will change the
frequency as you continue to turn the FREQUENCY knob, and the display will flash, indicating that
you are changing an existing program.

Notice that you will not be able to dial in a frequency outside the equalizer band which you have
selected. The bands do overlap, so you can accomplish rather complex equalization tasks.

Note: If you select the 32 kHz sample rate, the high frequency band tops out at 16 kHz (680 Hz

- 16.0 kHz). The high frequency band ranges between 680 Hz and 20.0 kHz, as indicated
on the front panel, when you use either the 44.1 kHz or the 48 kHz sample rates.

When the center frequency which you want to cut or boost displays in the window, stop turning
the FREQUENCY knob. The display will flash, indicating that you have made a change in fre­quency. Listen for the equalization change which you have made to the program. If you wish to
accept this change to the preset, push the SAVE button. The MASTER display will show the
flashing letters "Sto" (Store). Push the SAVE button again and the 628 will record the change to
the preset program. This edits the program and permanently records the change. The display will
stop flashing and display the new frequency after you save the change.

Adjustments to the equalization bandwidth (Q) are just as easy. Start by giving the BANDWIDTH

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9

knob a slow turn until you feel a single click. The MASTER numeric display will show the current
bandwidth setting in the program for the frequency selected. Continued rotation of the knob will
change the bandwidth and the display will show the value in octaves.

Note: The 628’s bandwidth control has a logarithmic taper. You will notice a greater
change in value with each click as the ratio increases.

Bandwidth defines the width of the cut or boost centered at the equalization frequency. When
applying a boost, the bandwidth (in octaves) is measured between the points on the curve where
the signal drops 3 dB below the boost applied at the center frequency. When a cut is applied to a
signal, the bandwidth (in octaves) is measured between the points on the curve where the signal
drops 3 dB from “flat” response.

When you need to notch out an offending hum or buzz, use a narrow bandwidth setting of .3
octaves (0.30 oct.), to suppress only the offending frequency. To boost a wide range of frequen­cies use a broad bandwidth setting of 3 octaves (3.00 oct.), for a smoother response. Push the
SAVE button and the MASTER display will show the flashing letters “Sto”(Store). Push the SAVE
button again and the 628 will record your new bandwidth setting. This edits the program and
permanently records the change.

The amount of cut, or boost, determines the amount of change made at the equalizer center
frequency. Turn the CUT/BOOST knob slowly until one click is felt. The MASTER numeric
display will show the cut, or boost, (in decibels, dB) currently used in the processing preset.
Turning the knob further will change the cut, or boost, and the new value will show in the LCD
display. Push the SAVE button once and the MASTER display will show the flashing letters “Sto”
(Store). Push the SAVE button again and the 628 will change the program and record the new
amount of cut or boost.

An example ...

Let’s run through an example of making an equalization change to make sure that everyone is with
the program. We will add a 4 dB boost at 125 Hz with a bandwidth of 3 octaves on program #10.

1.) Start by rotating the PRESET NUMBER knob until the MASTER display reads “10.”

2.) Momentarily push the LOAD button.

3.) Now select the LOW equalization band by repeatedly pushing the Band Select

button to the left of the FREQUENCY knob until the LOW LED lights.

4.) Turn the FREQUENCY knob until the MASTER numeric display shows a

frequency of 125 Hz (.125 kHz).

5.) Next, turn the BANDWIDTH knob until the MASTER numeric display indicates

3 octaves (3.00 oct.).

6.) Rotate the CUT/BOOST control until a 4 dB boost is indicated (+4.0 dB).

7.) Finally, push the SAVE button. Note that the MASTER display shows the “Sto”

message. Push the SAVE button a second time.
That’s it! You’ve changed the equalization and modified program #10.
Note: You can find more advice on equalizer theory and adjustments in Chapter 4.

The Compressor ...

Now we’ve graduated from equalization school and it’s time to move on to compressor college.
The COMPRESSOR section of the 628 operates the same way as the equalizer. When you move
any of the knobs one click, the MASTER display identifies the current value. Moving the knob
further than one click changes the value of the function. Make sure that the COMPRESSOR

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section is active by momentarily pushing the Operate/Bypass button to the right of the RELEASE
control until the ACTIVE LED comes on.

10

The THRESHOLD knob sets the COMPRES­SOR threshold level. Audio signals arriving
at the COMPRESSOR stage above the set
value (in dBu) will trigger the COMPRESSOR
into action. Signals arriving at the COM­PRESSOR below the threshold level will pass
through unaltered.

COMPRESSOR

-9 -15 -18 -12 -3 -6 ACTIVE

To change the threshold level, gently turn the
THRESHOLD knob until you feel one click.
The MASTER numeric display will show the
present threshold level in dBfs (decibels full­scale). For example: if the THRESHOLD control is adjusted so that the MASTER display shows
a value of “-30” the threshold is now set at a value 30 dB below clipping. Since the 628 clips at
+22 dBu, the threshold is set at -8 dBu (+22 dBu minus 30 dB).

To change the threshold value, turn the knob until the new threshold level which you want is
displayed. To save the change, momentarily press the SAVE button in the MASTER section. The
MASTER display will show the flashing letters “Sto” (Store). Push the SAVE button again and the
628 will record the change to the threshold. This edits the program and permanently records the
change. The new threshold value has now been loaded into the program. The LED meter in the
COMPRESSOR section will now display the amount of compression applied when a signal is
present.

Use the RATIO control to vary the compression ratio of the COMPRESSOR. Use low ratios (for
example: 2:1) for gentle level control. Save the higher ratios (for example: 5:1) for more aggressive
processing (rock & roll DJ use). Change the ratio by turning the RATIO knob until a single click is
felt. The numeric display in the MASTER section will show the current ratio expressed in a value
to 1 (for example: XX:1). To change the ratio, rotate the RATIO knob until the desired ratio appears
in the MASTER numeric display. Save the change by pressing the SAVE button. The MASTER
display will show the flashing letters "Sto" (Store). Push the SAVE button again and the 628 will
record the change to the preset program. This edits the program and permanently records the
change. You will note the result of the change in compression on the LED meter in the COMPRES­SOR section.

THRESHOLD

(dBFS)

RATIO

(X:1)

RELEASE

(Sec)

The RELEASE control allows you to change the release time of the COMPRESSOR. Long release
times (for example: 2.0 Sec.) produce gentle, transparent processing. Fast release times (for
example: .5 Sec.) result in aggressive, hard compression which some may find irritating. Most
operators compromise and select a release time somewhere in the middle range. Find what release
time the current preset uses by turning the RELEASE knob until one click is felt. The value in
seconds will display in the MASTER numeric display window. If you need to change the release
time, turn the RELEASE knob until the desired time is shown on the numeric display. Pushing the
SAVE button causes The MASTER display will show the flashing letters “Sto” (Store). Push the
SAVE button again and the 628 will record the change to the release time. This edits the program
and permanently records the change. You will note a change in the amount of compression on the
LED meter in the compressor section of your 628.

We have one more knob to turn before we weigh anchor on the compressor. The 628’s compressor
lowers the output level in direct proportion to the amount of compression which you dial in. When
you see the 628 compressing your voice by 6 dB, you will notice that the output level drops by
about 6 dB.

Here's where we use the OUTPUT LEVEL control to compensate for the signal lost in compression.
Grab the OUTPUT LEVEL knob and turn it until the number “6” appears in the MASTER display.
This adds 6 dB of gain to the output of your 628. Check for clipping on the MASTER output
meter. If everything looks OK, push the SAVE button twice to save this change to your compres­sor program.

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11

Note: Please reserve the use of the OUTPUT LEVEL to make up gain lost to the compressor. Do

not use the OUTPUT LEVEL control as an output attenuator. When you use the control
as an attenuator, you alter the gain structure of the 628 in the DSP and raise the overall
noise floor of the unit.

Note: You will find more advice on using an audio compressor in Chapter 4.

The Expander/Gate ...

Symetrix 528s and 528Es provided only a
THRESHOLD control for their downward
expander function. In response to our user’s
requests we enlarged the expander, creating a
separate EXPANDER/GATE section with
RATIO and RELEASE time controls. The
628’s RATIO control allows this new section
to perform either as a downward expander,
gently lowering the signal level when it falls
below the threshold value, or as a gate, and
essentially turning off a signal which falls
below the threshold. Use the EXPANDER/
GATE for single-ended noise reduction to turn down any studio background noise when no one is
speaking into the microphone.

By now you can probably figure out how to make adjustments to the EXPANDER/GATE controls.
They function just like the controls on the COMPRESSOR stage. Toggle the Operate/Bypass
button to the right of the RELEASE knob to activate the EXPANDER/GATE stage. Next, turn the
THRESHOLD control gently until one click is felt. The MASTER numeric display will show you
the current threshold level below clipping (dBfs). Turn the THRESHOLD knob further to raise or
lower the threshold. Press the SAVE button and the MASTER display will show the flashing
letters “Sto” (Store). Push the SAVE button again and the 628 will record the threshold change.

THRESHOLD

(dBFS)

EXPANDER/GATE

-12 -18 -15 -6 -9 -3 ACTIVE

RATIO

(X:1)

RELEASE

(Sec)

In the same manner, the RATIO knob activates the display and changes the ratio of the EX­PANDER/GATE stage. Selecting a low ratio (for example: 2:1) will cause the stage to behave like a
downward expander. When the input signal falls below the threshold, the 628 will lower the signal
at the ratio which you have chosen. In the example of a 2:1 ratio, a 1 dBu drop in the input signal
will result in a 2 dBu drop in the output signal level. The EXPANDER/GATE LED meter will reflect
the amount of downward expansion applied to the input signal.

If a higher ratio (10:1) is used, a 1 dBu drop in the input signal will result in a 10 dBu drop at the
628’s output. This resembles the function of a gate which turns off the signal when it falls below
the threshold level. Turn the RATIO knob until one click is felt and the MASTER numeric display
will show you the current program ratio (XX:1). Change the ratio by turning the knob further, and
save the change by pushing the SAVE button. The MASTER display will show the flashing letters
"Sto" (Store). Push the SAVE button again to record the change to the ratio.

The RELEASE time control tells the 628 how quickly to lower the signal level when the input audio
level falls below the defined threshold level. A short release time (for example: .500 Sec.) combined
with a high ratio (for example: 10:1) provides rapid, aggressive gating action. A sports announcer
would use this combination to minimize loud background noise when broadcasting a basketball
game. A long release time (for example: 2.50 Sec.) and a low ratio (for example: 2:1) provides gentle,
transparent downward expansion. This combination would work well in a studio to minimize air
conditioning noise or the sound of computer fans.

Slowly turn the RELEASE knob until a single click is felt. The MASTER display will show the
current release time. Change this value by continuing to turn the knob, watching the release time
value change on the display. Don’t forget to save the change by pushing the SAVE button. The

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MASTER display will show the flashing letters “Sto” (Store). Push the SAVE button again to
record the release time change.

12

The De-Esser ...

A de-esser functions as a frequency selective compressor. It lowers (compresses) the energy around a
chosen frequency. The THRESHOLD of the DE-ESSER
determines the level at which compression begins. De-essing
action begins if the input signal contains enough energy at the
specified frequency to rise above the threshold.

Push the Operate/Bypass button to turn on the DE-ESSER
section and light the ACTIVE LED. Turn the FREQUENCY
knob until a single click is felt. This will cause the MASTER
numeric display to show the current DE-ESSER frequency
setting (for example: 6.0 kHz.) Turning the FREQUENCY
knob further will change the frequency. Push the SAVE button
twice to record the change to the preset program.

A slow turn of the THRESHOLD knob, until one click is felt, will instruct the 628 to display the
threshold value on the MASTER numeric display. Turning the knob further will change the
threshold value. Pushing the SAVE button twice to record the change to the threshold value.

Note: You will find more information on de-essers in Chapter 4.

That’s it ...

You now can teach everyone else in the station how to use the 628, unless you don’t want to.
There are some things which are best kept secret. If you don’t want your air-talent to tweak the
parameters of their processing presets you can disable the 628’s front panel controls. After you
lock out the front panel controls, the announcers can switch between presets, but when they turn
other knobs the 628 ignores them.

-18

FREQUENCY

(kHz)

DE-ESSER

-12

THRESHOLD

-6

(dBu)

-3 ACTIVE-9 -15

Front Panel Security

Here’s how to lookout the 628’s front panel. With your index finger smartly extended, push the EQ
BAND SELECT button on the front panel and hold it in. Turn the PRESET NUMBER knob until the
MASTER display reads "LO" (Lock Out). Release the BAND SELECT button. You have now
disabled all digital front panel functions except for PRESET NUMBER selection. Anyone attempt­ing to change the operating values can twist knobs all day long, but the 628 will ignore their
attempts.

When you need to reactivate the front panel controls, hold the EQ BAND SELECT button in and
rotate the PRESET NUMBER knob until the MASTER display reads "uLO" (unLOck). The 628's
controls will now function.

Note: Since the microphone preamp and line input GAIN control and switches are analog

functions, you cannot lockout these controls. We provide security only for the digital
control functions of the 628.

Other remaining mysteries ...

If you remain puzzled by anything happening with your new 628, check Chapter Four, Audio
Processing Basics. This presents an overview of audio processing theory and may fill in the

missing bit of information which prevents you from fully understanding your 628. Chapter Five,
Troubleshooting, covers possible problems your unit might experience due to improper connec­tions, etc. Call us if there is anything which you just can’t figure out.

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Audio Processing Basics Chapter 4

The Symetrix 628 combines digital audio processing algorithms with a three-band digital parametric
equalizer. This chapter offers a tutorial on the basics of dynamic range processing (compression)
and equalization. This combination of processing serves as the mainstay of the vocal signal
processing chain used in recording studios. The tutorial information is intended to provide a
background for the operation instruction found in this manual.

Dynamic Range Processing

Dynamic range processors fit wide-range signals into narrow-range transmission or storage
channels. The dynamic range of acoustical signals found in real life far exceeds our capacity to
store or transmit them. Confronted with this dilemma, audio engineers usually reach for a compres­sor/limiter or downward expander as the means to fit two-pound signals into one-pound bags.

Compressor/limiters respond quickly to transients, and gently to normal speech level changes,
which keeps overall levels in check. The downward expander’s operation is the inverse of the
compressor/limiter. The expander can prevent “pumping” and “breathing”, even during high ratio
compression. Because the compressor/limiter and the downward expander interact, avoid “cross­ing” their thresholds by setting the downward expander’s threshold higher than that of the compressor.

Strictly speaking, the terms compressor and limiter refer to different devices. Often, manufacturers
combine both into a single device called a compressor/limiter. Functionally, a compressor/limiter
lets the user define the maximum level of an audio signal. Compressor/limiters perform as either a
compressor or a limiter, but not both at once.

Expanders and gates perform the opposite function of compressors and limiters. Compressors
continuously reduce (compress) the dynamic range of signals above a set threshold, while expand­ers continuously increase (expand) the dynamic range of signals below a threshold. Limiters can
be thought of as very high ratio compressors, and gates can be thought of as very high ratio expanders.

In addition to their roles as remedial signal processors, compressors serve a creative role. You can
use a compressor to improve the consistency of the voice by removing or reducing level changes
and adding power or “punch.” Generally speaking, the fluctuations of some voices may be extreme,
so experimentation is the name of the game. One combination of operating parameters will not
suffice for all voices.

Defining Dynamic Range

To begin a discussion of dynamic range processors it’s necessary to have a working definition of
dynamic range. The term is really self-descriptive, but has two distinct uses: To describe the actual
range of signal fluctuations that can pass through a piece of equipment. To define the maximum
allowable natural range of signal fluctuations. The unit of measure for audio signals is the decibel (dB).

Dynamic Range as a Specification

The maximum usable range of operation for a particular piece of gear is the difference in dB
between the noise floor and the maximum output level before clipping. In this context, dynamic
range becomes an equipment specification.

The noise floor definition is the lower limit of a circuit’s operating level, a function of its self­generated electrical noise. Very noisy circuits have a high noise floor, quiet circuits have a low
noise floor. All circuits, even very quiet ones, have measurable noise.

The maximum output level of a circuit becomes the upper limit of usable operation. Clipping of the
audio waveform begins at this point because the signal level exceeds the capacity of the power
supply. To put levels in perspective they must be referenced to some nominal operating level, like
0 dBm (1 milliwatt across 600 ohms). That’s why noise specifications are stated as negative
numbers. Since maximum output level is usually greater than 0 dBm (+4 dBu), it’s stated as a
positive value (above 0 dBm). The difference between the noise floor and the onset of clipping

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defines the dynamic range.

14

Dynamic Range of Sound

The other definition of dynamic range describes the natural range over which signals fluctuate.
The signals under discussion are electrical representations of sounds, so it follows that sound has
dynamic range. The dynamic range of the human voice, from a whisper to a shout, is over 100 dB.
An accurate microphone converts the sound pressure of a voice going from a whisper to a shout
into an electrical voltage having the same dynamic range.

Why Audio Compressors are Our Friends

To keep audio signals below distortion and above the noise floor, their natural dynamic range must
remain within the specified dynamic range of the circuits through which they pass. Unfortunately,
the actual dynamic range of real world signals exceeds the available dynamic range of even the best
audio processing equipment.

For example, the dynamic range of the best analog tape recorders calculates to around 80 dB, while
digital recorders top out around 96 dB. As good as these machines are, there’s still not quite
enough room for the very wide dynamic range of unprocessed audio. In order keep signals 60 dB
above the noise floor, the dynamic range of audio recorded on the analog tape recorder would have
to be restricted to 20 dB of dynamic range (80 dB minus 60 dB equals 20 dB). Signals recorded on
the digital recorder would have to be restricted to 36 dB of dynamic range (96 dB minus 60 dB
equals 36 dB).

A compressor or limiter reduces the dynamic range by setting an upper limit on the larger signals.
In some cases, it’s better to put processing to work on the lower end of the dynamic range rather
than on the upper end. In other words, instead of reducing the amount of change at the upper end
of the dynamic range with a compressor or limiter, we could increase the amount of change at the
lower end of the dynamic range with a downward expander or gate. In practice we throw away
some of the low level audio down near the noise floor.

Compressors are to Limiters as Downward Expanders are to Gates

Compressors reduce the dynamic range of their output whenever the input signal rises above the
set threshold, while downward expanders increase the dynamic range of their output whenever the
input signal falls below a set threshold.

Compressors, limiters, expanders and gates increase or decrease signal levels by some ratio. Good
compressors have an adjustable ratio, a ratio of the input level to the output level which is user­adjustable. A compressor operating with a 2:1 ratio allows only a 1 dB increase in output level for
every 2 dB increase in input level.

Limiters operate at high ratios (greater than 10:1). At 10:1, the limiter allows only a one dB increase
in the output level for every 10 dB increase in the input level. Limiters can be thought of as high­ratio, high-threshold compressors. They “stay out of the way” until the level goes above the
threshold. Above threshold their action becomes pronounced.

The Threshold Concept

A dynamic range processor’s activity begins once the input signal rises to, or falls below, a
predetermined level. In operation, the dynamic range processor’s sensing circuitry constantly
“looks at” the incoming signal and compares it to a reference level, the threshold level. The
operator sets that reference level via the threshold control. Remember, compressors and limiters
respond when signals at the input rise above threshold, while downward expanders and gates
respond only when signals at the input fall below the defined threshold.

Attack and Release Timing

If a compressor responded instantly to each waveform which crossed the threshold we would have
one very busy device. A signal passing through it would become a roar of constant level audio

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15

quickly tiring anyone listening for an extended period. The compressor would purge all dynamic
range; only the frequency would vary. Heavy compression with short attack and release timing
made AM radio loud in the ‘60s, but it drove listeners to FM radio and cassette tape. “Listener
fatigue” on the AM band killed their audience by robbing their program material of all dynamic
range. Compression becomes an asset when we moderate the rate of correction.

The attack time control tells the compressor how quickly to apply compression after signals rise
above the threshold. You may compare this to how hard you step on the gas pedal in your car
when you want to accelerate. You can take nine seconds to get to 55 mph, or you can step on the
accelerator gently and take several minutes to reach 55 mph.

We state attack time as a function of decibels (of compression) per millisecond; it is a rate of
attack. This describes how much compression is applied per millisecond once the signal crosses
the compressor threshold. Using an attack time of 1.0 dB/mSec results in the application of
compression at a rate of 1 dB every millisecond until the compressor satisfies its ratio and thresh­old requirements.

Audio containing a wide dynamic range and irregular wave forms (speech and hard rock music)
require short attack timing for tight control. Music sounds more pleasant as longer attack times
allow occasional short duration peaks to pass through without compression. Broadcast final
limiters function with very short attack timing to eliminate modulation overshoots. Audio clipper
circuits produce absolute overshoot protection (a brick wall) with instantaneous attack times.

Release timing tells the compressor how slowly to release compression after responding to a falling
signal peak. It is a rate of release. You may compare this to how firmly you step on your car’s
brake pedal when you want to slow down. How quickly do you want to stop?

Release timing is best expressed as decibels (of compression) per second. A release time of 10 dB/
Sec allows the compressor to release compression at a rate of 10 decibels every second. The faster
the release time, the more aggressive the compressor operation.

Speech, with its irregular wave forms, can tolerate faster release than music which contains
smoothly shaped sine waves. Use short release timing for aggressive processing, but remember
what happened to AM radio. Slower (longer) release timing preserves more dynamic range of the
source audio.

Linear vs. Downward Expanders

Expander operation brings confusion unless it’s remembered that the expander modifies the
dynamics, the changes, of signals passing through the circuit. An expander converts a slowly
rising audio voltage into a rapidly rising audio signal; it amplifies the change. Expanders come in
two types: linear and downward.

Linear expanders increase the dynamic range of all signals, no matter what their actual level. The
linear expander simply makes all changes greater by some ratio, sometimes user adjustable. In the
real world, linear expanders aren’t too practical because clipping occurs when signals just below
maximum output level expand upward.

For instance, an unprocessed signal 3 dB below clipping that increases 2 dB won’t distort, because
it’s still 1 dB below maximum. But if that same signal passes through an expander operating at a 1:2
ratio, the same 2 dB change at the expander’s input becomes a 4 dB change at its output. That
signal would expand to 1 dB over maximum, causing distortion. Use linear expanders with care,
because very few systems have enough headroom to handle the upward dynamic range which
linear expanders can produce.

The term “expander” generally describes a downward expander, because the device only expands
signals which drop below a threshold. The downward expander gives the operator the ability to expand
the usable dynamic range of audio passing through the system without running out of headroom.

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Note: In the interest of clarity, the term expander will be defined as a downward

expander from this point forward.

16

How Expanders Increase Usable Dynamic Range

The lower limit restriction of a system is the noise floor. Keep in mind that while the signal levels
may change greatly, the noise usually remains at a constant level. The action of the expander
increases the dynamic range of all signals below threshold. This action increases the apparent
loudness of signals above the expander’s threshold, while decreasing the apparent loudness of the
noise.

An expander operating at a ratio of 1:2 causes an input signal that falls 10 dB below threshold to
fall 20 dB at its output. The downward action of the expander reduces the noise floor by the same
ratio applied to the signal. Since the relationship between the signal and the noise stays the same,
the noise drops 20 dB by the action of the expander, which responds to the signal’s 10 dB drop at
the 1:2 ratio.

De-essers

The de-esser is another dynamic range controller specially designed to regulate high frequency
content. The de-essing technique was developed for motion picture dialogue recording. Speech
sounded more natural and pleasing with the reduction of sibilants. By sensing and limiting certain
selected frequencies, the de-esser provides specific control over some of the higher frequency
vocal sounds which may become overemphasized when the speaker or vocalist is close to the
microphone.

The 628’s de-esser controls excessive sibilant vocal sounds which can often range 12 dB louder
than the rest of the spectrum. It’s a frequency conscious compressor/limiter. The de-esser
operates only on the problem frequencies. Unlike brute force equalization, the de-esser can reduce
the offending sounds without sacrificing intelligibility. Because it operates dynamically, a de-esser
removes only sounds that are disproportionately loud, and only those falling within the selected
control range.

De-essers include knobs that allow the operator to control which frequencies are compressed, and
how much attenuation is applied. The 628’s DE-ESSER controls are FREQUENCY (800 Hz to
12 kHz) and THRESHOLD which may be set from 0 dB to -60 dB.

Equalization

Equalization is the most powerful tool available to the audio engineer. It is routinely the first
signal modification device that most people experience.

The parametric equalizer of the 628 allows both creative and corrective frequency shaping. It can
create a more pleasing sound and correct frequency response problems. The term “parametric”
refers to the fact that the primary operating parameters of the equalizer may be altered by the user.
The adjustable parameters are: center FREQUENCY (expressed in kHz), BANDWIDTH, or “Q”
(expressed in octaves), and the amount of CUT or BOOST (expressed in dB).

The center frequency is the frequency (kHz) in the middle of the bell shaped response curve formed
by a tuned filter. Bandwidth defines the width of the bell shaped curve, measured between its -3
dB points. The measure of bandwidth in audio equalizers is expressed in octaves or parts of an
octave. We express amounts of cut or boost in decibels at the center frequency of the bell curve.

Equalization is selective amplification, or reduction, of a signal based on frequency. Audio signals
consist of combinations of fundamental signals and their harmonics. Changes to the spectral
balance of a signal involves altering the relationship of the fundamental to its harmonics. Each
harmonic makes up one aspect of the audible character of a signal. Knowing these relationships
allows you to quickly zero-in on the correct frequency range of the signal and apply boost or cut to
enhance or correct what you are hearing.

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The audio spectrum contains several critical portions that comprise our perceptions of the sounds
which we hear.

Range Frequency Range Description
Low Bass 16 - 64 HZ Thunder, Large jet rumble
Bass 64 - 256 Hz Drums, bass violin
Midrange 256 - 2048 Hz Telephone sound, horn speakers
“Lisping” Quality 3000 Hz “Hissing” sounds
Presence Range 4750 - 5000 Hz Vocal clarity, enunciation
Brilliance 6500 - 16000 Hz Air & mouth noises

Using the Parametric Equalizer

Exercise care when using equalization; you may get too much of a good thing! The following
paragraphs give some general tips and precautions for using the 628’s parametric equalizer.

Beware of Distortion and Noise

When boosting a frequency or group of frequencies, the overall operating level rises. For example,
12 dB of boost (no matter what the frequency) increases the 628’s output level by 12 dB at that
frequency. This kind of boost consumes headroom by 12 dB in every circuit from the 628’s
equalizer to the last device in the signal chain. Unless signal levels remain very low, the 628’s
output stage may run out of headroom.

The 628's CLIP LED in the headroom meter monitors levels in the equalizer section plus the output
stage of the 628. If the CLIP LED flashes, try bypassing the equalizer. If this eliminates the
clipping indication, then reduce the amount of boost in the equalizer section. You may also reduce
the input level to the equalizer section by lowering the input GAIN control.

If the input signals to the 628 are too low, using the equalizer for boost may increase noise to
unacceptable levels. If your source signal levels are too low, increase the preamp gain if you use
the microphone input. You may need to raise the output level of the device feeding the 628’s line
input if you use a line level input signal.

Know What You Are Listening To

Low frequency boost may increase the level of some frequencies that you cannot hear. Many high
quality microphones generate substantial output at very low frequencies (below 50 Hz) which most
monitor speakers or headphones cannot reproduce. Be aware that the true effects of low fre­quency boost may not be audible but could result in a “muddy” or distorted sound.

Use Wide Peaks, Narrow Dips

The human ear prefers wide bandwidth peaks and narrow bandwidth cuts. Boosting a narrow
bandwidth produces a sound usually perceived as “offensive”. Boosting wider bandwidths (.7
octave or greater) usually results in a sound deemed “musical”. It has also been observed that very
few people will notice anything missing when a narrow bandwidth (.3 octave or less) is cut, even
by as much as 30 dB. But, a wide bandwidth cut results in a sound quality often called “empty”.

Tuning the EQ/Notch Filter

For both cut and boost, the 628’s parametric equalizer works at specific frequencies. To find a
particular frequency “by ear,” turn the CUT/BOOST control all the way up to +15 dB. Set the
BANDWIDTH for .3 octave. Tune the frequency control until you distinctly hear the part of the
sound which you wish to control. Then adjust the CUT/BOOST control for the appropriate

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amount of change, and readjust the BANDWIDTH control to cover the band of frequencies which
you want to change.

18

Equalizing for Speech

In broadcasting, equalizers create a sonic personality for the station’s on-air talent. The 628 allows
individual equalization for each voice. You no longer need to compromise on equalizer settings.

Here are some general thoughts on speech equalization:

1.) Try to use wider bandwidths. Narrow bandwidths (.5 octave and less) remain less

audible and are only useful for remedial work. Broader bandwidths prove less obnox­ious, more pleasant-sounding, and easier to work with.

2.) Try to avoid massive amounts of boost or cut. If you’re only trying to impart a flavor

(like sprinkling salt and pepper on a meal), then 6-8 dB of boost or cut should be all that
you need.

3.) A wide bandwidth cut equals a boost at the frequencies on either side of the cut.

4.) A quick way to figure out what’s going on is to set the level of one band of the equal-

izer to full boost (+15 dB), then switch to the FREQUENCY control and vary the
frequency of that band while listening to program material. This usually makes quick
work out of finding the frequency region which needs work. Now reduce the CUT/
BOOST control to something tasteful.

A common problem when trying to set an equalizer for someone’s voice is converting the descrip­tive adjectives that people use in describing the character of a voice into numbers in the 628’s
MASTER display window. Below are commonly used adjectives and their frequency ranges.

Frequency Description

75 - 200 Hz Rumble, fullness
200 - 300 Hz Bass, bignes s
400 - 600 Hz Chesty, warmth
600 - 1000 Hz Volume
2 - 4 kHz Clarity
3 - 5 kHz Nasal, yell, presence
5 - 8 kHz Enunciation, intimacy
10 kHz up Air, mouth noises (ask your dog)

To tailor your station’s announce sound, begin with an idea of what general sound you want.
Since you only have three choices of frequencies to equalize, you’ll need to begin with the aspects
of your sound which are most important. Every microphone imparts its own equalization to every
word which it hears, and this in turn makes your choice of microphone very important.

If you want a “bassy” sound, think about using a single-D cardioid microphone. The built-in bass
boost caused by close-talking a single-D microphone (its proximity effect) can be tamed and
tailored with equalization, which reduces room-rumble at the same time. Since the proximity effect
increases as the announcer moves closer to the microphone, a skilled user can substantially
change their sound simply by moving in or out from the microphone.

For clarity, a variable-D microphone, or an omnidirectional type, remains the best choice as these
microphones do not emphasize the bass frequencies when you close-talk them. On the negative
side, any room rumble will be boosted along with the voice if you try to boost lower frequencies.

Next, add or remove low frequencies in the 100 - 300 Hz range until you get a pleasing amount of
weight or fullness. Next add midrange boost in the 2.5 kHz to 5 kHz range to add punch and
presence (experiment with the bandwidth control), and finally add or remove frequencies in the 10
kHz range for brilliance.

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Solutions to Possible Problems Chapter 5

No analog output signal.

1.) Verify that the 628 is receiving AC power. Check the MASTER display for a reading.

2.) If not, try another device at that outlet or power strip.

3.) Have you selected the correct input source at the MIC/LINE switch?

4.) Does the MASTER headroom meter show signal presence?

5.) If not, check the input cables and connections.

6.) If the 628’s LED meter is active, check the output cables and connections.

7.) Verify that you are not connecting a microphone level output to a line level input.

8.) Have you connected a digital output to an analog input?

No digital output signal.

1.) Verify that the 628 is receiving power. Check the MASTER display for a reading.

2.) Does the MASTER headroom meter show signal presence?

3.) If not, check the input cables and connections.

4.) Have you selected the correct input source at the MIC/LINE switch?

5.) If the 628’s LED meter is active, check the output cables and connections.

6.) Is the rear panel digital output format in the proper position? Does your digital input

want AES/EBU or S/P DIF?

7.) Is the rear panel SAMPLE RATE SELECT switch in the proper position? It must reflect
the sample rate of the digital recorder, workstation, etc.

8.) Do you have the digital output of the 628 connected to a digital input?

Hum or buzz in the audio.

1.) Verify that you have seated all connectors firmly.

2.) Try substituting input and output cables. We’re testing for a broken connection in a

cable.

3.) Is all equipment in the system properly grounded? There may be a ground loop

between units. This occurs when a voltage difference exists between grounds.

“Ground” is not always ground.

4.) Is all equipment connected to the same AC ground? Plug all into the same power strip.

Distorted audio.

1.) Does the CLIP LED in the microphone preamp light? If so, turn down the GAIN control

or push in the 15 dB PAD switch.

2.) Does the MASTER headroom meter show clipping? Possibly the equalizer is clipping.

Turn down any large amounts of EQ boost.

3.) Does the MASTER headroom meter still show clipping; all LEDs lighted. If so, check

4.) Bypass all processing functions one at a time; the ACTIVE LED will be off. If this

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the MASTER OUTPUT LEVEL control for a large amount of digital gain, or lower the
input signal at the preamplifier.

clears the distortion, check the program parameters for unusual or extreme settings.

5.) Verify that the 628’s output level is correct for the mixer input level. Are you feeding a

line level signal into a preamp input? If so, convert one of the 628’s XLR outputs to
microphone level. See Appendix C.

6.) Is the PHANTOM LED on? Use phantom power only with BALANCED (3 conductors

on the plug) condenser, or electret, microphones.

7.) Check the source audio quality with another device. “Garbage in” equals “garbage

out.”

Noise in the form of hiss.

1.)Check the input signal level. Is the GAIN control set between 9:00 o’clock and 12:00

o’clock? Is the -15 DB PAD button in the out position?

2.)Check the equalizer section for large amounts of boost (+10 dB, or more) above 1 kHz.

3.)Do the compressor LEDs display large amounts of compression?

4.)Check the digital gain by turning the OUTPUT LEVEL knob until one click is felt. The

MASTER display should show “0.” If not, turn the knob for a “0” reading.

5.)Verify that the 628’s output level is correct for the mixer input level. Are you feeding a

line level signal into a preamp input?

6.)Check the source audio quality with another device. “Garbage in” equals “garbage

out.”

No processing action.

1.) Verify that the processing stage (de-esser, expander, compressor or equalizer) is

activated. The ACTIVE LED associated with that stage must be on.

2.) Are you trying to modify one of the factory presets? Presets 120-127 are read-only; you

must move the program to another location before you can modify it. Check Chapter 3
for instruction on moving presets to new locations.

3.) Check the RATIO control. Low ratio settings, 2:1 or less, produce very little processing

action. Read Chapter 4 on audio processing theory.

4.) Check the THRESHOLD control value. No processing takes place until the signal level

passes the threshold. Is your threshold set too high? Review Chapter 4.

5.) Are you in the bypass preset? The MASTER display will read "byP". This is a read-

only preset with no processing and flat equalization.

The SAVE button does not operate. I cannot save changes to a preset.

1.) Are you trying to make changes to a factory preset (#120-127)? These are read-only

programs; you cannot change them. To change a factory preset, copy the preset to
another location and then the 628 will let you modify the program.

2.) Are the front panel controls locked out? See Chapter 3 for the lockout instructions.

The MASTER display shows a value outside of the normal operating limits.

1.) If a program buffer of a processing preset becomes corrupted the MASTER display will

try to display the erroneous value. For example: The equalizer CUT/BOOST value may
read “-99” in the MASTER display. This is outside of the equalizer's normal range.
Turn the CUT/BOOST control until a value between -15 and +15 is displayed. Next,
push the SAVE button twice. This should correct the problem.

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2.) If the problem persists at that particular preset, erase the preset and start from scratch.

With the PRESET NUMBER control select and load the bypass program. Turn the
PRESET NUMBER knob again until the offending preset's number is displayed in the
MASTER display. Push the SAVE button. The MASTER display will show the
message “Sto”. Push the SAVE button a second time. The offending program has been
erased completely and you can dial in the processing settings of your choice.

The 628 is locked-up.

1.) Verify that front-panel lockout is not engaged. If the front panel controls are in the

“secure” mode you may switch between presets, but you will not be allowed to change
any of the operating parameters. If the lockout function is engaged, see the last few
paragraphs of Chapter Three for instructions on how to unlock the controls.

2.) Are you in the bypass preset? The MASTER display will read “byP”. This is a read-

only preset with no processing and flat equalization. You may turn the knob, but
nothing happens.

3.) Check the MASTER DISPLAY for an error code. Examples:

“...” (flashing) = Initialization error
“E20” = DSP boot error The DSP has failed to boot from the host.
“E21” = DSP communication error. The DSP is not responding to the host.
“E22” = DSP host vector error. The DSP is not answering a host command vector.
“BAT” = Your memory backup battery is failing.

Oh $#!T! Skip to the re-initialization procedure below, or call Symetrix Customer Service at (425)
787-3211 with your 628’s serial number (on a bar-coded label on the bottom of the unit) and the
Error Code number.

4.) If you are unable to switch between presets your 628 could be trying to run on cor-

rupted software caused by a brief power interruption or by dirty power. First try
unplugging your 628 from the AC power, count to ten, then plug it back in again. If this
fails to correct the problem, you must re-initialize the 628; this reloads the operating
software from memory.

The Re-initialization Procedure, or everything I know is wrong ...

Note: Re-initialization of the 628 reloads the operating program from memory. All user

created processing presets will be erased.

1.) Re-initialize the 628. Push both the LOAD and SAVE buttons. The MASTER DISPLAY

will show the flashing letters “INI.”

2.) If you REALLY want to proceed with re-initialization, ERASING ALL OF YOUR USER

PRESET PROGRAMS, push the SAVE button. If you reconsider, and do not want to re­initialize, then push any non-locking button on the 628’s front panel EXCEPT the SAVE
button.

Should you decide to return your 628 to Symetrix for service, please adhere to the instructions in
the following section.

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Repair and Warranty InformationChapter 6

Return Authorization

Symetrix will service any of its products for a period of five years from date of manufacture.
However, no goods will be accepted without a Return Authorization number. Before sending
anything to Symetrix, call us for an RA number. Just ask, we’ll gladly assign you one! Call (425)
787-3222 weekdays, 8:00 AM to 4:30 PM, Pacific Time.

In-Warranty Repairs

To get your unit repaired under the terms of the warranty:

1. Call us for an RA number.

2. Pack the unit in its original packaging materials.

3. Include your name and shipping address, plus a brief statement of the problem. Your
daytime telephone number is very useful, in case we can’t verify your problem.

4. Put the RA number on the outside of the box.

5. Ship the unit to Symetrix, freight prepaid.

Just do these five things, and repairs made under warranty will cost you only the one-way freight
expense. We’ll pay the return freight.

If you want to speed things up, you can return you unit by UPS Blue or Red, or you may use
Federal Express. We will return your repair using premium freight at no additional charge. If you
return you unit by parcel post or UPS surface, please don’t ask us to return it to you via overnight
or second-day service.

If you don’t have the factory packaging materials, then do yourself a favor by using an oversize
carton, wrap the unit in a plastic bag and surround it with bubble wrap. Fill any empty space in the
carton with bubble wrap. Be sure there is enough clearance in the carton to protect the rack ears.
We won’t return the unit in anything but new, original Symetrix packaging. If the problem turn out
to be operator inflicted, you’ll have to pay for both parts and labor. In any event, if there are
charges for the repair costs, you will pay for return freight. All charges will be COD unless you
have made other arrangements (prepaid, Visa or Master Card).

Out-of-Warranty Repairs

If the warranty period has passed, you’ll be billed for all necessary parts, labor, packaging materi­als, and any applicable freight changes.

Remember, you must call for an RA number before you send your unit to Symetrix. Follow the five
steps in the In-Warranty instructions above.

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Symetrix Limited Warranty Chapter 7

Symetrix 628 Digital Voice Processor Limited Warranty

Symetrix expressly warrants that the product will be free from defects in material and workman­ship for one (1) year. Symetrix’ obligations under this warranty will be limited to repairing or
replacing, at Symetrix’ option, the part or parts of the product which prove defective in
material or workmanship within one (1) year from date of purchase, provided that the Buyer
gives Symetrix prompt notice of any defect or failure and satisfactory proof thereof. Products
may be returned by the Buyer only after a Return Authorization number has been obtained
from Symetrix and the Buyer will prepay all freight, and customs duty, to return any products
to the Symetrix factory. Symetrix reserves the right to inspect any products which may be the
subject of any warranty claim before repair or replacement is carried out. Symetrix may, at its
option, require proof of the original date of purchase (dated copy of original retail dealer
invoice). Final determination of warranty coverage lies solely with Symetrix. Products re­paired under warranty will be returned surface freight prepaid via United Parcel Service by
Symetrix, to any location within the Continental United States. When the Buyer returns a
product for warranty repair by overnight, or second-day transportation, Symetrix will return
the repaired unit via UPS Blue or Red service at no additional change. Outside the Continental
United States, products will be returned freight, and customs duty, collect.

The foregoing warranties are in lieu of all other warranties, whether oral, written, express,
implied or statutory. Symetrix, expressly disclaims any IMPLIED warranties, including fitness
for a particular purpose or merchantability. Symetrix’s warranty obligation and buyer’s
remedies hereunder are SOLELY and exclusively as stated herein.

This Symetrix product is designed and manufactured for use in professional and studio audio
systems and is not intended for other usage. With respect to products purchased by consum­ers for personal, family, or household use, Symetrix expressly disclaims all implied warran-

ties including, but not limited to, warranties of merchantability and fitness for a particular
purpose.

This limited warranty, with all terms, conditions and disclaimers set forth herein, shall extend
to the original purchaser and anyone who purchases the product within the specified warranty
period. Warranty registration must be completed and mailed to Symetrix within thirty (30)
days of the date of purchase. This limited warranty gives the buyer certain rights. You may
have additional rights provided by applicable law.

Symetrix does not authorize any third party, including any dealer or sales representative, to
assume any liability or make any additional warranties or representation regarding this product
information on behalf of Symetrix.

Limitation of Liability

The total liability of Symetrix on any claim, whether in contract, tort (including negligence) or
otherwise arising out of, connected with, or resulting from the manufacture, sale, delivery,
resale, repair, replacement or use of any product will not exceed the price allocable to the
product or any part thereof which gives rise to claim. In no event will Symetrix be liable for
any incidental or consequential damages including but not limited to damage for loss of
revenue, cost of capital, claims of customers for service interruptions or failure to supply, and
costs and expenses incurred in connection with labor, overhead, transportation, installation or
removal of products or substitute facilities or supply houses.

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SpecificationsChapter 8

Inputs

Controls and Switches: Gain, 15 dB Pad, Phantom Power,
Mic/Line

Input Connector: Microphone - Female XLR,

Microphone Input Circuit: Balanced Transformerless, Low Z

Phantom Power (DIN 45 596): +48 Volts, Nominal
Microphone Pad: 15 dB (± 3 dB)
Microphone Preamp Gain: 15 dB (Min. gain) to 75 dB (Max.

Microphone Input Maximum Level: -3 dBu (Min. gain) to -52 dBu

Microphone Equivalent Input Noise (EIN): < 120 dBV (20 Hz to 20
kHz)
Microphone Preamp CMRR: > -60 dB

Line Input Circuit: 10 K Ohm, Transformerless Balanced Bridging
Line Input Level at 0dBFS: -10 dBu to +21 dBu
Line Input Nominal Level: +4 dBu
Line Input CMRR: > -40 dB (+20 dBu, 20 Hz to 20 kHz)

Dynamic Range Processor

Type: Digital Compressor/Limiter/Expander/Gate
Compressor Ratio Range: 1:1 - 15:1
Compressor Release Time Range: 250 mS. to 5.0 Sec.
Compressor Threshold Range: -60 dBFS to 0 dBFS
Expander Ratio Range: 1:1 - 10:1
Expander Release Time Range: 250 mS. to 5.0 Sec.
Expander Threshold Range: -60 dBFS to 0 dBFS
De-esser Type: Digital High-Cut Filter, 12 dB/Octave
De-esser Frequency Range: 800 Hz to 12 kHz
De-esser Threshold Range: -60 dBFS to 0 dBFS

Equalizer

Type: Digital Three-Band Parametric
Bands: 20 Hz to 500 Hz, 160 Hz to 6300 Hz,

Bandwidth Range: .3 to 4 Octaves
Maximum Cut/Boost: ±15 dB

Line - Female XLR & TRS Jack

(150-ohms)

gain, ±3 dB, Pad Out)

(Max. gain, Pad Out)

(60 dB Gain, 20 Hz to 20 kHz)

680 Hz to 20 kHz

Analog Output

Type: Balanced Transformerless
Output Level at 0dBFS: +22 dBu Balanced, Jumperable

Connectors: Male XLR (2) & TRS Jacks (2)
Output Source Impedance: 200 Ohms, Balanced
Minimum Load Impedance: 600 Ohms Balanced or Unbalanced

Digital Output

Type: AES/EBU and S/P DIF
Connectors: AES/EBU - Male XLR, S/P DIF - RCA Female
Sample Rates: 32 kHz, 44.1 kHz, 48 kHz

Overall Performance

Frequency Response: ±1.0 dB (20 Hz to 20 kHz)
THD: 0.05% (20 Hz to 20 kHz) +4 dBm

Output
Noise: <-89 dBu (20 Hz to 20 kHz)
A/D & D/A Converters: 20 bit, Delta-Sigma
Internal delay: <5 mS.

MIDI Implementation

Access: MIDI Program Change, MIDI Program Dump
MIDI Channel Range: 1 to 16
Connectors: MIDI In, MIDI Out
Programs: 8 Factory Presets, 1 Bypass, 119 User

Physical

Size (HWD): 1.75 x 19 x 6.5 in.

Weight: 5.5 lbs (2.5 kg) net

Electrical

Backup Battery Type Lithium BR2016, rated 3.3 V,

Caution: These servicing instructions are for use by qualified
personnel only. Replace only with same type Lithium BR2016,
rated 3.3 V, 4 mA max. current.

Requirements for US/Canadian models: 117 VAC Nominal,

to +16dBu or -20dBu for mic level input

Presets, 128 Total

4.45 x 48.26 x 16.5 cm

10 lbs (4.6 kg) Shipping

4 mA max. current

(Symetrix part #039400)

105 to 125 VAC, 50 to 60 Hz

(UL and C-UL listing applies only to this rating)

15 Watts maximum

Requirements for Export models : 220 VAC Nominal

205 to 225 VAC, 50 to 60 Hz

15 Watts maximum

Caution: In the interest of continuous product improvement, Symetrix, Inc. reserves the

right to alter, change, or modify these specifications without prior notice.

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Architect's and Engineering Specifications Chapter 9

The digital voice processor shall be capable of microphone signal amplification, simultaneous de­essing, downward expansion or gating, variable-ratio compression and parametric equalization.
The processor shall operate on user-selectable sample rates of 32 kHz, 44.1 kHz or 48 kHz. The unit
shall allow the user to create, store in memory and recall 119 processing presets. The manufacturer
shall provide one bypass program and eight factory presets in read-only memory.

The unit shall have a low-noise, low-distortion microphone preamplifier with switchable (on/off)
phantom power. A 15 dB switchable pad shall be provided to attenuate high-output microphone
signals. A front panel switch shall be provided for switching between microphone and line level
(+4 dB, nominal) signals. When the line-level input is selected the microphone input circuit shall
be disconnected.

A digital de-esser function shall offer frequency-selective attenuation of up to 18 dB. The de­esser shall be adjustable within the range of 800 Hz to 12 kHz. There shall be front panel frequency
and threshold controls as well as a bypass switch.

A digital downward expander/gate function will provide the user with a noise reduction function.
The expander shall have a variable threshold with a range from 0 dBFS to -60 dBFS. A front panel
ratio control shall be adjustable between a 1:1 to 10:1 range. An expander release time control shall
be adjustable between 250 milliseconds and 5.0 seconds. A front panel bypass switch shall
disengage the expander/gate function.

The digital compressor section shall have a user-adjustable ratio control operating through the
range of 1:1 to 15:1. A front panel threshold control shall have a range of 0 dBFS to -60 dBFS. The
compressor release time shall be adjustable in the range from 250 milliseconds to 5.0 seconds. A
front panel bypass switch shall disengage the compressor/limiter functions.

The cascaded, three-band, digital parametric equalizer shall offer overlapping bands of: 20 to 500
Hz, 160 to 6300 Hz and 680 to 20 kHz. A front panel switch shall toggle control and adjustment
between low, midrange and high equalizer functions. The equalizer section shall include a bypass
switch.

The analog outputs shall be selectable between line level (+4 dB nominal) and microphone level
(-40 dB nominal) by internal jumpers. The analog output shall be provided on two male XLR
connectors and two tip-ring 1/4 inch jacks.

The digital output shall accommodate both AES/EBU and S/P DIF formats. The AES/EBU output
connector shall be a male XLR connector. The S/P DIF output connector shall be an RCA female
jack. Output format selection shall be made with a rear panel push button switch.

MIDI control shall be provided through rear panel MINI input and MIDI output connectors. A
MIDI channel select switch shall provide operation on MIDI channels 1 through 16. A MIDI
program dump push-button switch shall transfer all programs from one digital voice processor to
another. An optional MIDI remote program selector shall provide access to programs 1 through 11
plus a bypass program (0). The voice processor shall supply power for the remote program
selector.

The digital voice processor shall operate by means of an internal power supply connected to 117
VAC, 50/60 Hz or 230 VAC, 50 Hz power.

The unit shall be the Symetrix, Incorporated, model 628 Digital Voice Processor.

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Symetrix 628 Factory PresetsAppendix A

Factory Preset Description
Preset 120 Velvet Voiced FM Announcer

Minimal processing for the “already good” radio voice. Features light expander
action, a 2:1 compression ratio, with a bass and high frequency EQ boost.

Preset 121 Country Music Jock: aka “Bubba Budweiser™”

Offers medium expander action with a 2.5:1 compression ratio for tighter control. Uses
a larger bass and high frequency boost in the EQ than Preset 120.

Preset 122 Top 40: The 3x5 card reader.

Provides medium expander and compressor processing. Boosts the low end by 5 dB
and a 4 dB boost in the high frequencies.

Preset 123 Rock ‘N’ Roll Animal: Get your shots!

Tight voice control with a large low frequency boost. Higher ratios in both the
expander and compressor. Fast release times in both.

Preset 124 Ms. News: Crisp & squeaky clean.

Provides medium processing for the female voice. Don’t use this only for news, it
may be your best choice for female jocks.

Preset 125 Mr. News: The Voice of Doom.

Includes medium processing with a heavy low-end boost. These settings also work
well for AM talk show hosts.

Preset 126 Susie Sweetheart: On-The-Air here often?

Features light expander operation, medium processing in the compressor. The EQ is
set for a bass boost and a high frequency peak at 3.0 kHz. Lower the high band boost
if this is to sibilant.

Preset 127 The Weekend Guy: Looks as bad as he sounds.

Aggressive de-esser action and tight expander control for the voice which needs
help. Medium control in the compressor followed by a bass and high frequency
boost.

We offer these presets as starting points for your individual custom presets. Try one of these factory
presets and make the necessary changes to fine tune the processing. They all include a 6 dB boost at
the OUTPUT LEVEL knob to compensate for compression.

Presets 120 through 127 are read-only programs. The 628 will not allow you to make changes to these
presets. You will want to copy one of the above presets to a new location, then make any adjustments
necessary to suit the individual voice. Check out the instructions in Chapter Three.

Call us if you have questions after you have read Chapter Three!

“Budwiser” is a registered trademark of Anheiser Busch.

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Symetrix 628 Preset Worksheet Appendix B

Photocopy this page and preserve a written record of your custom presets.

Preset# Preset#Name Name

De-Esser De-Esser

Frequency:

kHz

Frequency:

kHz

Threshold: Threshold:

Expander/Gate Expander/Gate

Threshold: Threshold:

Ratio: Ratio:

Release: Release:

Compressor Compressor

Threshold: Threshold:

Ratio: Ratio:

Release: Release:

Parametric EQ Parametric EQ

Low Band Low Band

Frequency: Frequency:

dBFS dBFS

dBFS dBFS

:1 :1

Sec. Sec.

dBFS dBFS

:1 :1

Sec. Sec.

kHz kHz

Bandwidth: Bandwidth:

Cut/Boost: Cut/Boost:

Mid Band Mid Band

Frequency: Frequency:

Bandwidth: Bandwidth:

Cut/Boost: Cut/Boost:

High Band

Frequency: Frequency:

Bandwidth: Bandwidth:

Cut/Boost: Cut/Boost:

Oct. Oct.

dB dB

kHz kHz

Oct. Oct.

dB

kHz kHz

Oct. Oct.

dB dB

628

Output Level Output Level

28

dB dB

dB

High Band

Output Level ConversionAppendix C

Converting an Analog XLR Output to Microphone Level:

We shipped your 628 with its analog line outputs configured for line level output (+4 dBu). We
recommend that you use the 628 configured this way and use a line level input on your mixing
console. The microphone preamp in the 628 exhibits better performance characteristics than those
found in most consoles. Don’t throw away all this gain by padding down the output unless you
absolutely must.

If you must use a microphone level input one, or both, of the 628’s XLR outputs convert to
microphone level output (-40 dBu) with internal jumpers. This feature allows one XLR output
configured to microphone output level while one XLR remains at line level.

Note: The 1/4 inch TS outputs may not be switched to microphone level. These remain unbal-

anced, line level outputs only.

Here’s the procedure:

1.) Unplug all connectors from the 628 and remove it from the rack.

2.) Remove the top cover. Don’t forget those pesky 3/32 inch allen screws in the front

panel.

3.) Locate the ANALOG OUTPUT XLR connectors on the rear panel.

4.) Immediately behind the chassis XLR connectors find black pin jumpers J6 and J7, or

J10 and J11, depending on which XLR output you want to convert to microphone level.

5.) Move both jumpers next to the output connector which you want to convert to

microphone level rearward to the jumper pins closest to the XLR connector.

6.) Replace the top cover and all retaining screws.

7.) Reinstall the 628 in your rack.

8.) Connect the power and audio cables.

Changing the Maximum Analog Output Operating Level

When the 628 is shipped from the factory its maximum output level before clipping is +22dBu (as
referenced to 0dB full scale digital on the digital outputs). Provisions to pad the maximum level of
the balanced outputs to +16dBu or -20dBu are provided via the internal jumpers J4, J5, J7, J9, J10
and J12.

30

C28

31

C25

C34

C31

J3

J6

L9

R44

R43

C36

D1

J4

J5

BP17

U11

BP14

C32

R41

BP18

C35

R49

U12

BP20

R45

R47

R46

C42

R48

C39

U14

BP22
C40

2

R52

C43

C45

G

C50

BP23

C48

R53

G

1

3

R51
C47

BP24

L10

R59

R60

J7

R57 R61

U16

R65

C51

R66

C52R58R54

C53

C56

C54

J8

R64

R69

L14

R78

R77

J10

R70

R71

U19

J9

R68

C58

BP26

R72

C59

L13

2

C61

C63
R79
BP28

BP29

C62

BP30

BP31

C64

3

R82

R81
C65

R83

1

J11

C66

R85

U21

U22

J12

L15
R87

R88

J13

BP33

D3

Jumper positions

for +22dBu

maximum output.

U24

628

29

R30

C28

R31

C25

C34

C31

J3

J6

L9

R44

R43

C36

D1

J4

J5

BP17

U11

BP14

C32

R41

BP18

C35

U12

R45

R49

BP20

R47

R46

C42

R48

C39

U14

BP22

C40

G

1

2

3

R52

C43

C45

C50

BP23

C48

R53

R51
C47

BP24

L10

R59

R60

J7

R57 R61
U16

R65

C51

R66

C52R58R54

C53

C56

C54

J8

R64

R69

L14

R78

R77

J10

R70

R71

U19

J9

R68

C58

BP26

R72

C59

L13

2

C61

C63
R79
BP28

BP29

C62

BP30

BP31

G

C64

3

R82

R81
C65

R83

1

J11

C66

Jumper positions

for +16dBu

maximum output.

R85

U21

U22

L15
R87

R88

J12

BP33

J13

D3

U24

R30

C28

R31

C25

C34

C31

J3

J6

L9

R44

R43

C36

D1

J4

J5

BP17

U11

BP14

C32

R41

BP18

C35

U12

R45

R49

BP20

R47

R46

C42

R48

C39

U14

BP22

C40

G

1

2

3

R52

C43

C45

C50

BP23

C48

R53

R51
C47

BP24

L10

R59

R60

J7

R57 R61
U16

R65

C51

R66

C52R58R54

C53

C56

C54

J8

R64

R69

L14

R78

R77

J10

R70

R71

U19

J9

R68

C58

BP26

R72

C59

L13

2

C61

C63
R79
BP28

BP29

C62

BP30

BP31

G

C64

3

R82

R81
C65

R83

1

J11

C66

R85

U21

U22

L15
R87

R88

J12

BP33

J13

D3

U24

Jumper positions

for -20dBu

maximum output.

628

30

Appendix D

The Symetrix RC-1 MIDI Remote Control

We offer the Symetrix RC-1 as an accessory remote control for the 628 Digital Voice Processor.
The RC-1 provides limited control; it allows the user to select and load the first eleven user
programmed processing presets of the 628. The RC-1 also makes provision for selection of a
BYPASS function, which is Program 0 on the 628. The RC-1 may be used with other MIDI
controlled equipment to select Programs 0 thru 11.

Caution: The Symetrix RC-1 includes a jack for an optional 9 VDC power supply (not sup

plied). If you use the RC-1 with the 628, the RC-1 takes its power from the 628. No
external power supply is required when using the RC-1 with the 628. The optional 9
VDC connection allows you to use the RC-1 with other MIDI controlled devices.

The RC-1 does not provide selection or change of any individual processing parameters. It selects
and loads presets #0 through #11 only. Changes to the 628’s processing presets must be made at
the processor’s front panel. There is no button lockout or other security feature provided on the
RC-1. If you accidentally hit one of the buttons, you will accidentally change the processing preset
on the 628.

The RC-1 connects to the Symetrix 628 with a 25-foot, 7-pin DIN cable. We provide this cable
with the RC-1. The 628 and RC-1 exchange MIDI information on pins #2 and #3. The 628
provides power for the RC-1 on pins #1 and #7. Pin #7 carries +5 VDC; pin #1 is ground. To
preserve compatibility with other MIDI devices, the remaining pins on the connector are not used.

RC-1 Remote Control

If the RC-1 is used with other MIDI controlled equipment, a standard 5-pin MIDI cable may be
used. A 5-pin MIDI cable plug will connect directly into the female 7-pin DIN socket on the RC-

1. When the RC-1 is used with any device other than the Symetrix 628, power must be provided
by the user with a 9 VDC supply plugged into the power jack on the rear of the RC-1 Remote
Control. We ship the RC-1 configured to identify itself as MIDI Channel #1.

PROGRAM 1

PROGRAM 2

PROGRAM 3

PROGRAM 4

PROGRAM 5

PROGRAM 6

PROGRAM 7

PROGRAM 8

PROGRAM 9

PROGRAM 10

PROGRAM 11

BYPASS (PROGRAM 0)

What’s my name?

You may change the MIDI channel identification of the RC-1 by the use of four solder jumpers on
the bottom of the RC-1 circuit board. The table on the following page identifies the jumpers which
must be bridged with solder to identify the RC-1 for each possible MIDI channel. The “X”
indicates a jumper requiring solder closure. Do not solder across the jumpers marked “0”. Please
note that J4 is on the left and J1 is on the right (just as in the table).

628

31

MIDI Channel J4 J3 J2 J1

1 0000
2 000X
3 00X0
4 00XX
50X00
60X0X
7 0 XX0
8 0 XXX
9 X000
10 X00X
11 X0 X0
12 X0 XX
13 XX0 0
14 XX0 X
15 XXX0
16 XXXX

To change your RC-1’s MIDI identification, disconnect all connectors from the RC-1. Remove
the chassis bottom by taking out the screws in both sides of the RC-1. Lift the bottom cover off.
Locate J1, J2, J3 and J4 in the rear center of the circuit board. Solder together the jumpers marked
with an “X” in the table which correspond with the desired MIDI channel identification. Replace
the bottom cover and retaining screws.

Installation ...

After installing the 628 in its permanent position you may connect the RC-1. Position the RC-1 Remote
Control in a convenient, but secure location. Route the 25-foot cable between the two devices. Secure
the cable so that it is not a tripping hazard or located where it could be damaged by moving equipment
or furniture. Good news! Both ends of the cable are male; you can’t install it backwards.

Plug the cable into the DIN socket on the rear of the RC-1. Next, connect the cable to the MIDI/
RC-1 IN socket on the rear of the 628. While you’re there, please check that the MIDI CHAN­NEL switch on the 628 is set for Channel 1.

You will notice that none of the LEDs on the RC-1 are lighted when it is first plugged in. This is
normal; the LEDs serve as tally lights indicating which button was pushed last. The LEDs do not
provide positive confirmation from the 628 that the program selected was loaded by the 628. The
RC-1 will not reflect a change in program selection made at the front panel of the 628. The LEDs
on the RC-1 serve as reminders of which button on the RC-1 the user pressed last.

MIDI OUT

POWER IN FROM

MANUFACTURED IN THE USA BY

LYNNWOOD, WA

628

NO USER SERVICEABLE PARTS INSIDE.

OPTIONAL EXTERNAL

POWER SUPPLY.

WHEN USED WITH

(NOT NEEDED

SYMETRIX 628)

9 VOLTS D.C.

D.C. POLARITY

TIP + RING -

SYMETRIX 628

32

Testing 1, 2, 3 ...

Push the button in the upper left corner of the RC-1. This is labeled PROG #1. The LED next to
the push-button will light. Verify that the 628 has loaded program #1. The MASTER display on
the front of the 628 will display the number 1. Push several other buttons on the RC-1 and verify
that the 628 loads the corresponding program. Please press only one button at a time.

You may write, in pencil please, your own identification for programs 1 through 11 on the spaces
provided on the RC-1 Remote Control. If you will faithfully use pencil, the names are easily erased
when changes become necessary. Ball-point pen markings can usually be removed with denatured
alcohol. Beware: unlike radio station staff, names entered with permanent markers usually remain
forever.

Note: Program #0, in the lower right corner of the RC-1, is a bypass only position with no audio

processing or equalization. The 628 does not allow user programming of Program 0.

Need a longer cable?

The RC-1’s cable uses a shielded cable of seven #22 gauge wires. You may build a longer cable,
or an extension cable, with 7-pin DIN connectors and shielded 7-conductor cable. If you build
your own remote cable of a length longer, or shorter, than the one supplied, both connectors will be
male. If you choose to build an extension cable for the RC-1, please use one male and one female
7-pin DIN connector. Pin #1 connects to pin #1 on the opposite end. Pin #2 connects to pin #2,
etc. Symetrix does not offer extension cables, or cables of different lengths.

Troubleshooting

The LEDs on the RC-1 do not light after a button is pushed.

1.) The RC-1 is not receiving power. Are the DIN connectors firmly seated in their

sockets on the RC-1 and the 628?

2.) Is the 628 operating? The RC-1 takes its power from the 628.

3.) If you use the RC-1 with a MIDI device other than the 628, you must provide an

external 9 VDC power supply. This plugs in next to the remote control cable on the RC-1.

A LED on the RC-1 lights after a button is pushed but the 628 does not select and load the
requested processing preset.

1.) The RC-1 is not communicating with the 628. Are the DIN connectors firmly seated on

each end of the cable?

2.) Has the 628’s MIDI channel been changed to anything other than Channel #1?

3.) Has your remote control cable been damaged?

The RC-1 loads any processing preset, #1 through #11, except one. For example: When you push
the button for preset #5, the LED on the RC-1 for preset #5 does not light and the 628 does not
switch to preset #5. All other presets buttons operate properly.

1.) The switch for preset #5 (in this example) is broken or contaminated.

2.) Has anyone spilled a soft drink or coffee on the RC-1?

3.) The RC-1’s circuit board has been damaged by brute force.

The RC-1 loads all presets properly but one LED on the RC-1 does not light when the corre­sponding button is pushed.

1.) The LED is defective. Has it been broken or pushed down into the RC-1 chassis?

Please call the Customer Service Department at Symetrix for additional help or for repair parts. Dial
[phone] between 8:00 AM to 4:00 PM, Pacific Time.

628

33

Input/Output Connections Appendix E

FROM BALANCED OUT

FEMALE XLR

PIN 1 = GROUND

PIN 2 = HIGH

PIN 3 = LOW

FROM BALANCED OUT

MALE TRS PLUG

TIP = HIGH

RING = LOW

SLEEVE = GROUND

FROM UNBALANCED OUT

MALE TS PLUG

SLEEVE = GROUND +

TIP = HIGH

LOW

MALE RCA PLUG

SLEEVE = GROUND +

TIP = HIGH

LOW

FROM BALANCED OUT

TERMINAL STRIP

(+) = HIGH

(-) = LOW

= GROUND

2

3

1

SLEEVESLEEVE

TO BALANCED IN

1

3

2

TO BALANCED IN

TIPTIP

RINGRING

TO UNBALANCED IN

MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +

MALE RCA PLUG
TIP = HIGH
SLEEVE = GROUND +

TO BALANCED IN

MALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW

MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND

LOW

LOW

TERMINAL STRIP
(+) = HIGH
(-) = LOW

= GROUND

FROM BALANCED OUT

(TO UNBALANCED IN)

TERMINAL STRIP

(+) = HIGH

(-) = NOT USED

= GROUND

FROM ELECTRONIC, NON-TRANSFORMER

BALANCED OUTPUT (TYPICAL OF SYMETRIX PRODUCTS)

PIN 1 = GROUND + LOW

TO UNBALANCED INPUTS

FEMALE XLR

PIN 2 = HIGH

PIN 3 = NOT USED

MALE TRS PLUG

TIP = HIGH

RING = NOT USED

SLEEVE = GROUND+

LOW

2

3

1

TIP

RING

SLEEVE

TO BALANCED IN

(FROM UNBALANCED OUT)

TERMINAL STRIP
(+) = HIGH
(-) = UNUSED

= GROUND

TO UNBALANCED IN FROM

TRANSFORMER COUPLED OR

FLOATING BALANCED OUTPUT

MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +

MALE RCA PLUG
TIP = HIGH
SLEEVE = GROUND +

LOW

LOW

628

34

Declaration of ConformityAppendix F

Declaration of Conformity

We, Symetrix Incorporated,

14926 35th Ave West, Lynnwood, Washington, USA,

declare under our sole responsibility that the product:

628 Digital Voice Processor

to which this declaration relates,

is in conformity with the following standards:

EN 60065

Safety requirements for mains operated electronic and related

apparatus for household and similar general use.

EN 50081-1

Electromagnetic compatibility - Generic emission standard

Part 1: Residential, commercial, and light industry.

EN 50082-1

Electromagnetic compatibility - Generic immunity standard

Part 1: Residential, commercial, and light industry.

EN 55022

Limits and methods of mesurement of radio interference

characteristics of information technology equipment.

The technical construction file is maintained at:

Symetrix, Inc.

14926 35th Ave. West

Lynnwood, WA, 98037-2303

USA

The authorized representative located within the European Community is:

World Marketing Associates

P.O. Box 34

Newquay, Cornwall, TR7 1TU, U.K.

Date of issue: 13 May, 1997

Place of issue: Lynnwood, Washington, USA

Authorized signature:

Dane Butcher, President, Symetrix Incorporated.

628

35

628

36

Symetrix, Inc.

14926 35th Ave. West

Lynnwood, WA, 98037-2303

USA

Tel: [phone]

Fax: [phone]

Website: http://www.symetrixaudio.com

Email: [e-mail]