Symetrix 528 User manual

Symetrix Inc.
14926 35th Avenue West
Lynnwood, Washington 98037
voice: [phone]
[phone]
fax: [phone]
1
Symetrix
528
Voice Processor
'
'
.M'^
Owner’s Manual
6/3/fy
Rev 1.2,4/15/94
Part number: 530196
Subject to change at our whim, and without notice.
Copyright (c) 1992-1994, Symetrix Inc. All rights reserved.
Batteries not included. Ground isn’t ground!
Available at finer studios everywhere.
No part of this manual may be reproduced or transmitted in any form or by any
means, electronic or mechanical, including photocopying, recording or by any
information storage and retrieval system, without permission, in writing, from
the publisher.

FOREWORD
This manual contains all the information you need to operate the 528 Voice Processor.
There are seven chapters. The individual sections of each chapter are labeled first with
the chapter number, then with the section number. For example, the first section of the
first chapter is labeled 1.1, and the third section of the fourth chapter is labeled 4.3,
and so on. Use the numbers referenced in the Table of Contents to quickly locate the
information you need.
IF YOU’RE GOING TO JUMP RIGHT IN AND START USING THE 528 WITHOUT READING THE
MANUAL, JUST TAKE AMINUTE TO RUN THROUGH SECTION 3-FAST FIRST TIME SETUP.
Several different notation conventions are used to indicate various facets of the 528’s
features:
CAPS indicate amarked feature on the 528,
like the bypass switch, or the INPUT
connector.
Boldface and ,are used for emphasis. Bold type
italics carries more weight than italic type.
Some of the text in this manual is set apart by one of the headings Note, or Caution:
NOTES convey useful information that’s included to make certain functions more obvious,
and to supply extra information about processes, techniques, connectors etc.
CAUTION indicates apotential danger to the 528 or associated equipment. An example of
aCAUTION can be found below.
CAUTION
Save the original box, packing material, and purchase receipt. If ever
it^s necessary to ship your unit it must be packaged in its original box
to prevent damage, and the receipt may be required as proof of
purchase for warranty repairs. (See Section 7.)
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Table of Contents
1-Introduction -•^
1.2 Microphone Preamplifier 1
1.3 Phantom Power 1
1.4 Downward Expander, Compressor/Limiter 2
1.5 Defining Dynamic Range 3
1.6 Dynamic Range as aSpecification 3
1.7 Dynamic Range of Sounds and Signals -3
1.8 Why Dynamic Range Processrors are Necessary 4
1.9 Compressors are to Expanders as Limiters are to Gates 4
1.10 The Threshold Concept ^
1.11 The VGA ^Voltage Controlled Amplifier ..5
1.12 Linear vs. Downward Expanders 5
1.13 How Expanders Increase Usable Dynamic Range 5
1.14 Sidechain Processing 3
1.15 De-esser. 3
1.16 Parametric Equalizer/Notch Filter —-V
2. Using the 528 8
2.1 Getting Started —-........8
2.2 AWord About the Controls 8
2.3 Block Diagram -.......9
2.4 Input /Output Connections -...........10
2.5 Patching/ Sidechain Connections ................11
2.6 Mic Preamp Controls
2.7 De-esser Controls.
2.8 Dynamic Range Processor Controls ^3
2.9 Parametric Equalizer/Notch Filter Control s13
2.10 Output Gain Control ,Metering —
2.11 Installation
3. Fast First Time Setup -—.......15
3.1 Connections .......15
3.2 Mic Preamp Setup .......16
3.3 De-esser Setup -—
3.4 Dynamic Range Processor Setup -*
3.5 Parametric EQ/ Notch Filter Setup -
3.6 Output Settings .....16
3.7 Meter Readings
4. Applications ^^
4.1 Broadcast Applications
4.2 Using the Parametric EQ/ Notch Filter
4.2. 1Beware Distortion and Noise
4.2.2 Know What You Are Listening To ...18
4.2.3 Use Wide Peaks, Narrow Notches —......18
4.2.4 Tuning the EQ/Notch Filter ........18
4.2.5 Parametric EQ/Notch Filter Examples.... 18
4.3 Announce Mies -Compressing, Limiting, Expanding... 21
4.4 Using the De-esser .... 23
4.5 Cleaning Up News Feeds ..25
4.6 Increasing Gain Before Feedback........... ...................25
4.7 Parametric EQ in the Sidechain................... ....... ..26
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4.8 Using Sidechain EQ to Enhance Expander Action.. 26
4.9 Using Reverb or Effects 27
4.10 Vocal Processing -Recording and Reinforcement 27
4.11 Adding Dynamics, or ’’Punch” 28
4.12 High Level Stage Monitors ~Dynamic Processing 28
5. 528 Specifications 29
6.Troubleshooting Guide 3q
6.1 Troubleshooting Table
7. Service Information/Schematics 31
7.1 In Warranty Service 31
7.2 Out-of-Warranty Service 31
7.3 Schematic Diagrams
7.3.1 201750B -PCB Component Placement 32
7.3.2 191750B -Input Stages 33
7.3.3 191750B -De-esser
7.3.4 191750B -Compressor/Expander 35
7.3.5 191750B -Parametric EQ/Notch Filter 35
7.3.6 191750B Output Driver, Display, Power Supply ...37
7.3.7 191752A -Output Level Display 33
APPENDIX A-Using Electronically Balanced Inputs and Outputs ............39
APPENDIX B-Notes on the 528-01 (Option 1Transformer Coupled Output) 40
WARRANTY STATEMENT.. ......1*11^41
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1. Microphone Signal Processors
LI Introduction
The 528 Voice Processor contains five functions needed for microphone signal processing:
mic preamp (with phantom power), de-esser, downward expander, compressor/limiter, and
parametric equalizer. The 528"s ’'normal” signal chain includes all five functions, but the
de-esser, the dynamics processor (expander/ compressor/ limiter), and the parametric
EQ/ notch filter may be individually bypassed with front panel switches.
In addition, the versatility of the 528 is greatly enhanced by its patching capabilities.
Each section is brought out to its own set of normalled rear panel terminations ,so any
signal routing possibility is provided for, and patch bay installations are supported.
1*2 Microphone Preamplifier
The ultra low noise, low distortion mic preamp provides adirect-coupled balanced input,
for optimum transient response and phase coherency. Its positive going and negative
going slew rates are symmetrical, ensuring sonic intergrity. The mic preamp^s balanced
input gain may be adjusted with the front panel gain trim control, allowing it to handle
very high signal levels —up to -3dBV without overload.
13 Phantom Power
All condenser microphones require some kind of electrical power for operation. This
power may be supplied to the mic by internal batteries, an external power supply that^s
connected to the microphone by aspecial cable, or through the microphone cable by
phantom or ’T” System powering.
The 528 provides phantom powering for condenser microphones. The rear panel PHANTOM
POWER switch applies +48VDC to pins 2and 3 at the mic input XLR connector. Phantom
power is so named because it is "invisible” to audio signals, even though the microphone
cable carries both direct current (DC) phantom power, and alternating current (AC) audio
signals. Specifically, the term phantom power means apositive DC voltage applied to
the microphone via both audio leads, usually pins 2and 3of a3-pin XLR type
connector. This voltage is applied through current limiting resistors, which also serve to
isolate the audio leads from one another.
The phantom power technique uses the mic cable to deliver the power required by the
microphone, eliminating the need for an additional external power supply or internal
batteries. In this situation +48VDC is applied equally to both sides of afloating
balanced circuit, so no current flows through the microphone’s transformer, or through the
microphone element itself. However, if the circuit is unbalanced, current will flow. As
aresult, unbalanced mics can never be used with phantom power.
Phantom powering is not to be confused with ”P' System powering, sometimes called
modulation lead or AB powering. ’T” System powering applies power to only one audio
lead, using the other as power ground. Phantom powering and System powering are not
compatible without special adapters.
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It is often said that the sound of some dynamic microphones is affected by phantom
power, and that ribbon mics cannot be plugged into an input that is phantom powered.
For the most part these are myths that grew out of difficulties that occured as aresult
of some other problem in the mic circuit:
1. When XLR connectors are mated there is no guarantee that both pins 2
and 3will make contact at exactly the same time. It is possible that a
damaging current could flow through the mic for abrief moment under these
conditions. However, this is acon~nector problem, not aproblem with the
mic itself, or phantom power in particular.
2. If the mic’s output transformer has developed leakage, the microphone
may become noisy (crackling, sputtering or even humming) when phantom
power is turned on. The leakage, not the power, is the problem. The
available solutions are to turn off the phantom power, put a1:1 transformer
between the mic and the input, or get the mic repaired.
CAUTION
Do not use phantom power before consulting the microphone
manufacturer's literature. Many condenser microphones have non-
standard power requirements, and may be damaged by +48 volt
powering. Unbalanced microphones must not be used with phantom
powering.
1.4 Downward Expander, Compressor/Limiter
The 528 Voice Processor utilizes Symetrix^ program controlled interactive dynamic range
processing technique to combine the best attributes of both compressor/1imiters,and
expanders, ’’Program controlled” means the 528^s dynamic range processor section
analyzes incoming signals, then adjusts its attack and release times to match the
transient characteristics of those signals.
Levels are kept in check by the compressor/ limiter, which responds quickly to transients,
and gently to normal speech level changes. The downward expander^ soperation is the
inverse of the comp/limiter, so it prevents ’’pumping” and ’’breathing” even when high
ratio compression is necessary. Because the compressor/1imiter and the downward
expander are interactive, the 528 always responds appropriately, while providing
automatic control over awide range of input levels.
Strictly speaking, the terms compressor and limiter refer to two different devices.
However, the two are often combined into asingle device called acompressor/ limiter.
Compressor/1imiters usually perform as either acompressor or alimiter, but not both at
once. Functionally, acompressor /1imiter is adevice that lets the user define, or
predetermine ,the maximum level of an audio signal.
Expanders and gates are the functional opposites of compressors and limiters.
Compressors continuously reduce the dynamic range of signals that are above threshold,
while expanders continuously increase the dynamic range of signals that are below
threshold. Limiters can be thought of as very high ratio compressors, and gates can be
thought of as very high ratio expanders.
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1.5 Defining Dynamic Range
To begin adiscussion of dynamic range processors it's necessary to have aworking
definition of dynamic range. The term is really self-descriptive ,but has two distinctly
different uses:
1. To describe the actual range of signal fluctuations that are going
through the equipment, and
2. To define the maximum allowable range of signal fluctuations that can
be put through the equipment.
The usual unit of measure for audio signals is the decibel (dB).
1.6 Efynamic Range as aSpecification
The maximum usable range of operation for aparticular circuit or piece of gear is the
distance in dB between the noise floor and the maximum output level. In this context,
dynamic range is used as an equipment specification.
Noise floor is defined as the lower limit of acircuit's operating level, and is afunction
of its self—generated electrical noise. Very noisy circuits have ahigh noise floor, quiet
circuits have alow noise floor. The maximum output level is the upper limit of the
operating level, and is the level at which clipping begins. To put levels in perspective
they must be referenced to some nominal operating level, like OdBm. That’s why noise
specs are stated as minus something.
In the case of the 528, noise is refered to the input, and stated as equivalent input
noise (EIN). The noise specification is given this way because the gain of the 528's
input stage is variable, so the actual signal-to-noise performance of the unit becomes a
function of how much gain is used in the preamp. To find the signal—to—noise ratio at
OdBm output, subtract the preamp gain from the EIN.
Since maximum output level is usually greater than OdBm, it's stated as plus something.
The 528's maximum output level is +24dBm, which is 24dB above OdBm. The difference
between the noise floor and the onset of clipping is the dynamic range. To find the
528's dynamic range with 50dB preamp gain, subtract -87 from +24. llldB is the dynamic
range.
L7 Dynamic Range of Sounds and Signals
The other definition of dynamic range describes actual level changes, or the range over
which signals fluctuate. The signals under discussion here are electrical representations
of sounds, so it follows that sound has dynamic range. The dynamic range of the human
voice, from awhisper to ashout, is well over 1OOdB. So amicrophone will convert the
sound pressure of athe voice going from awhisper to ashout into an electrical output
signal with adynamic range of well over lOOdB.
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1.8
Why Dynamic Range Processors are Necessary
For signals to stay below distortion and above noise, their actual dynamic range must be
kept within the specified dynamic range of the circuits through which those signals flow.
Unfortunately ,the actual dynamic range of real world signals often exceeds the available
dynamic range of even the best equipment.
For example, the dynamic range of the best analog tape recorders is around 80dB, while
digital recorders top out at around 96dB. As good as these machines are, there's still
not quite enough room for very wide dynamic range signals. In order to maintain a60dB
signal-to-noise ratio (to keep the signals 60dB above the noise floor), the dynamic range
of signals stored on the analog tape machine would have to be restricted by 20dB, while
the digital recorder would be restricted by 36dB.
Acompressor or limiter is often used to reduce dynamic range by setting an upper limit
on the larger signals. However, in some cases it's better to put processing to work on
the lower end of the dynamic range than on the upper end. In other words, instead of
reducing the amount of change at the upper end of the dynamic range with acompressor
or limiter, increasing the amount of change at the lower end of the dynamic range with
an expander or gate.
1.9 Compressors are to Expanders as Limiters are to Gates
Compressors reduce the dynamic range of their output whenever the input signal is above
threshold, while expanders increase the dynamic range of their output whenever the input
signal is below threshold.
Compressors ,limiters, expanders, and gates increase or decrease signal levels by some
ratio. Compressors usually have an adjustable ratio, that is, the ratio of the input level
to the output level can be changed by the user. Acompressor operating with a2:1 ratio
would allow only aIdB increase in output level for every 2dB increase in input level.
Limiters usually have anon-adjustable ratio that is very high (greater than 10:1). At
10:1 ,the limiter allows only aIdB increase in the output level for every lOdB increase
in the input level. Limiters can be thought of as high ratio ,high threshold compressors.
They are intended to *'stay out of the way” until the level goes above threshold.
However, above threshold their action is very definite,
1.10 The Threshold Concept
The threshold is the level at which adynamic range processor's activity begins. In
operation, the dynamic range processor's sensing circuitry constantly "looks at” the
incoming signal and compares it to areference level, which is called the threshold
level. In practice that reference level is set by the operator with the threshold control
.
Remember, compressors and limiters respond when signals at the input are above
threshold, while expanders and gates respond only when signals at the input are lower
than the defined threshold.
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1.11 The VCA -Voltage Controlled Amplifier
The action of adynamic range processor is determined by one of the amplifier circuits
inside the unit whose gain is controlled by aDC voltage. That part of the circuit is
called avoltage controlled amplifier, or VCA. Inside the 528 aseparate buffered audio
signal is sent to agroup of circuits that comprise the detector. The detector circuits
turn the AC audio signal into aDC control voltage, which is sent to the VCA under the
direction of the front panel controls.
1.12
Linear vs. Downward Expanders
Expander operation is easily misunderstood unless it^s remembered that what's being
expanded is the dynamics, or changes, of signals passing through the circuit. Expanders
come in two very different 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, which is
sometimes user adjustable. Linear expanders can cause distortion, because clipping
occurs when signals just below maximum output level are expanded.
For instance, an unprocessed signal 3dB below clipping that goes up 2dB won't distort,
because it's still IdB below maximum. But if that same signal is passed through an
expander operating at a1:2 ratio, the same 2dB change at the expander's input would
become a4d3 change at its output. However, that signal would be IdB over maximum,
causing distortion. Linear expanders must be used with care, because very few systems
have enough headroom to handle the upward dynamic range increase they produce .
The kind of processor most commonly called an expander is really adownward expander,
because it only affects signals below threshold. This gives the operator control over the
expander's activities, allowing it to be used to expand the usable dynamic range of the
system without running out of headroom.
1.13
How Expanders Increase Usable Dynamic Range
The lower limit restriction of asystem is the noise floor, which is usually well below
the 528's lowest expander threshold (~60dBm). It's important to keep in mind that while
the signal levels may change greatly, the noise usually doesn't change very much. The
action of the expander increases the dynamics of all signals below threshold that do
change. This action increases the apparent loudness of those changing signals, while
decreasing the apparent loudness of the noise.
For example, an expander operating at aratio of 1:2 will cause asignal that falls lOdB
at its input to fall 20dB 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 is reduced 20dB by the action of
expander, which is responding to alOdB drop in the signal with its 1:2 ratio.
1.14
Sidechadn Processing
The sidechain is apatch point in the control circuit of adynamic range processor, which
provides access to the part of the circuitry that tells the VCA what to do. Ilie 528"s
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sidechain is routed through apair of rear panel barrier strip terminations that allow the
control signal to be processed outside the unit (see Section 2.4 for specific hookup
information).
Look at the block diagram in section 2.3. Notice the SIDECHAIN terminations that come
from the comp /limit /expand section. They allow access to the control circuit that is
taken from the audio signal at the dynamic range processor’s input. This control signal
is derived from, but kept totally separate from, the audio signal path. That means the
control signal can be processed outside the 528 without actually processing the signal
that’s going through the VGA (the audio signal itself). This presents some very
interesting possibilities for changing or improving the operation of the dynamic range
processor.
The best use of the sidechain is to make the action of the 528’s comp/ limiter/ expander
frequency dependent, that is, to make it respond more (or less) to certain frequencies.
Because the audio signal and the control signal remain completely separate (even while
the control circuit tells the VGA whether to turn the gain up or down), you can equalize
the sidechain without changing the EQ in the main audio path.
Removing unwanted frequencies from the control signal before it actually reaches the VGA
prevents those frequencies from being used to create gain changes. And perhaps most
importantly, this is accomplished without actually equalizing the signal being processed
through the 528. Applications utilizing the sidechain may be found in Section 4.
1.15 De-esser
Ade-esser is another type of dynamic range controller that’s specially designed to
regulate high frequency content. The technique was originally developed for motion
picture dialogue recording, when it was discovered that speech sounded more natural and
pleasing when the accentuation of sibilants was reduced. By sensing and limiting
certain selected frequencies, the de-esser is intended to provide more specific control
over some of the higher frequency vocal sounds that tend to become over emphasized.
Many sibilant vocal sounds like ”s,” ”sh,” and **t” are very difficult to reproduce
electronically, because they contain alarge percentage of very high frequency harmonics.
But because these sounds are so essential to the intelligibility of speech, they cannot
be simply removed with equalization. In fact, to help maintain articulation many sound
engineers boost the higher frequencies of the vocal spectrum (3kHz to 8kHz), and/or use
microphones with ’’presence curves.” However, in certain individuals sibilant sounds are
already over accentuated, and any kind of high frequency boost only exacerbates the
situation.
The 528’s de-esser controls excessive sibilant and fricative vocal sounds, which can
often be as much as 12dB louder than the rest of the spectrum. It’s activity is similar
to afrequency conscious comp /limiter (with an equalizer boosting the high frequencies in
its sidechain). Unlike acomp/limiter however, it operates only on the frequencies
selected. And unlike an equalizer the de-esser can reduce the offending sounds without
sacrificing intelligibility, because it operates dynamically. It removes only sounds that
are disproportionately loud, and only those that fall within the operator-s elected control
range.
De-essers usually include controls that allow the operator to determine which freqeuncies
are controlled* and how much those frequencies are actually attenuated. The 528/ sde-
6

esser controls are FREQUENCY, which is variable from 800Hz to 8kHz, and RANGE, which
may be set from OdB to 20dB. In other words, the 528’s de-esser will attenuate selected
frequencies between 800Hz and 8kHz as much as 20dB.
1.16 Parametric Equalizer/Notch Filter
The paramteric EQ/notch filter provides both creative and corrective frequency shaping’ —
it can be used to create amore pleasing sound, and to correct amplitude response
problems. It’s designed to provide an asymmetrical +15dB/-30dB boost/cut response to
allow any of its three bands to perform as equalizers or highly selective notch filters.
The term "parametric” simply refers to the fact that the operating parameters of the
equalizer may be altered. Those parameters that are user adjustable are (1) center
frequency (or f^, expressed in Hz), (2) bandwidth (sometimes called "Q," or selectivity,
expressed in octaves), and (3) the amount of cut or boost (expressed in dB).
1. Center Frequency is defined as the frequency (in Hz) at the middle of
the bell shaped response curve formed by afilter.
2.Bandwidth is the width of the bell shaped curve, measured between its
~3dB points. The measure of bandwidth in audio equalizers is usually
given in octaves or parts of an octave.
-3. Cut or Boost is given in dB, at the center frequency.
7

2. Using the 528
’’When all else fails, read the directions.”
2.1 Getting Started
This section of your manual will give you all the control and switch settings you need
to operate the 528. Brief descriptions of the control functions are provided here, while
Section 4includes examples of how the 528 is used, with thorough explanations of the
operation of each of the 528^ sprocessors.
IF YOU^RE GOING TO JUMP RIGHT IN AND START USING THE 528 WITHOUT READING THE
MANUAL, JUST TAKE AMINUTE TO RUN THROUGH SECTION 3-FAST FIRST TIME SETUP.
REMEMBER, THIS ONLY NEEDS TO BE DONE ONCE TO BECOME FAMILIAR WITH THE 528"S
CONTROLS -AFTER THAT IT'S EASY.
2.2 AWord About the Controls
With its variety of functions and associated controls, the 528 can be used effectively in
alarge number of situations. However, the level of performance you are able extract
from the 528 depends entirely on your understanding of the relationship between the
individual functions and controls.
23 Block Diagram
The functional block diagram in Figure 2.1 illustrates the signal flow into, inside of, and
out of the 528. Notice that the audio signal is routed through patch points between each
of the major sections, and that the sidechain of the dy namic range processor section is
available. These connections are all made on the rear panel barrier strips TBl and TB2.
NOTE
THE UNIT WILL NOT WORK WITHOUT ACOMPLETE CIRCUIT PATH
THROUGH ALL REAR PANEL PATCHING TERMINATIONS. Patching and
sidechain connections provide an output/input loop in the circuitry.
For signals to flow from the 528' smic or line input to its output,
the connection through these terminations must remain intact.
Therefore, the patching and sidechain terminations are ”normalled” by
shorting straps installed at the factory. All terminal pairs that must
be normalled are indicated by ”U” shaped chassis markings over the
barrier strips. The shorting straps may be removed when signals are
routed elsewhere for processing, or when individual sections of the
528 are used for signals not originated at the 528' sinput.
8

9

2.4 Input/ Output Connections
CAUTION
When the 528 is used as an input device in any system that includes
power amplifiers and loudspeakers, do not plu§ into either the mic or
line inputs while the system^s power amplifiers are **onJ* The 528 can
contribute substantial §ain to input signals, and very lar§e low
frequency transients may be produced at the 528^soutput when input
connections are made while the unit is **onJ' These transient signals
will not damage the 528, but when amplified, may damage loudspeakers.
MIC INPUT
A3-pin XLR connector is provided for microphone level input signals.
Pin 1=ground Pin 2=high (+) Pin 3=low (-)
Input impedance is balanced bridging (to match all low impedance
professional microphones). Maximum input level is -3dBV.
+48VDC phantom power may be applied through pins 2and 3of the MIC
INPUT connector by depressing the rear panel PHANTOM POWER switch.
CAUTION
Do not use phantom power before consulting the microphone
manufacturer's literature. Many condenser microphones have non-
standard power requirements, and may be damaged by +48 volt phantom
powering. In addition, some dynamic microphones may be damaged by
phantom powering. For more information, please refer to Section 1.3
Phantom Power (on paie 1).
LINE input
A1/4” 3-conductor TRS {Tip-Ring-Sleeve) connector, which is paralleled by
barrier strip terminals. Located on the rear panel, the TRS connector accepts
balanced or unbalanced signals. Use either 2-conductor (mono type) or 3-
conductor (stereo type) connectors. As shown in the block diagram in Figure
2.1 ,the TRS connections are:
Tip =high (+) Ring =low (-) Sleeve =ground (shield).
Terminals 1, 2and 3on barrier strip TBl are connected inparallel with the
1/4” TRS connector. Balanced or unbalanced line level input signals may
be connected here as well.
#1 =high (+)#2 =low (-) #3 ~ground
The balanced LINE INPUT impedance is 46.3k ohms. Unbalanced input
impedance is 23.1k ohms. Maximum input level is +18dBV.
10

STACKING INPUT
Apair of teminations on barrier strip TB2 for signals from another 528 ¥oice
Processor (or any other line level device). This input allows two 528"s to be
operated through asingle output. To stack two 528*s, connect the EQ OUT
patch from one 528 to the STACKING INPUT on the other 528. (The OUTPUT GAIN
controls remain separately active, as "submasters.**)
fn =signal #6 =ground
The STACKING INPUT impedance is >10k ohms, maximum input level is
+18dBm.
OUTPUT
A1/4 2-conductor (mono type) TS (Tip-Sleeve) connector, which is in parallel
with the barrier strip output terminals #8 and 10. Located on the rear panel,
the the 1/4" connector delivers unbalanced low impedance output signals.
Tip =signal Sleeve =ground (shield).
Terminals 8,9, and 10 on barrier strip TB2 deliver balanced output signals.
The connections are:
#8 =ground #9 =low (-) #10 =high (+)
Output impedance is 51 ohms, balanced or unbalanced. Minimum load
impedance is 600 ohms. Maximum output level is +24dBm balanced, +18dBm
unbalanced.
CAUTION
When the output is operated in an unbalanced configuration DO NOT
§round the unused le§. Doin^ so will unnecessarily load the output
driver, resulting in increased distortion and possible damage. See
Appendix A-Using ElectronicallyBalanced Inputs and Outputs.
2.5 Patching/Sidechain Connections
Output /Input patching connections are provided on the rear panel barrier strips TBl and
TB2, as shown in the drawing below. All terminations are unbalanced.
PATCHING
Output impedances are all <100 ohms ,miminum load impedance for all patching
outputs is 600 ohms. Maximum output level is +18dBm.
Input impedances are all >20k ohms. Maximum input level is +18dBV.

SIDECHAIN
The SIDECHAIN connections provide access to the dynamic range processor's
control circuit, via terminals 8, 9and 10 on barrier strip TBl
.
Output impedance of the SIDECHAIN is <100 ohms, minumum load impedance is
600 ohms. Maximum output level is +18 dBm. Input impedance is >20k ohms,
maximum input level is +18dBV.
NOTE
Patching and sidechain connections provide an output/ input loop in
the circuitry. For signals to flow from the 528’ sinput to output, the
connection through these terminations must remain intact. Therefore,
the patching and sidechain terminations are ”normalled” by shorting
straps installed at the factory. All terminal pairs that must be
normalled are indicated by ”U" shaped chassis markings over the
barrier strips. The shorting straps may be removed when signals are
routed elsewhere for processing, or when individual sections of the
528 are used for signals not originated at the 528’s input.
2.6 Mic Preamp Controls
PREAMP GAIN
Sets the gain of the microphone preamplifier, from 10 (3dB) at its most
counterclockwise rotation, to 50dB at its most clockwise rotation.
CLIP
Illuminates when preamp output levels reach +16dBm.
PHANTOM POWER
On the rear panel near the line output jack, this switch turns on +48VDC
phantom power for condenser microphones, applied via pins 2and 3of the XLR
input connector.
2.7 De-esser Controls
DE-ESS FREQUENCY
Selects the frequency range to be placed under the control of the de-esser.
DE-ESS RANGE
Determines how much the selected frequencies will be attenuated. At OdB the
de-esser is essentially out of the circuit, while at 20dB all signals within the
selected frequency range will be attenuated 20dB.
BYPASS
Enables /disables the de-esser.
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2.8 I^namic Range Processor Controls
EXPAND THRESHOLD
Sets the level below which the downward expander’s activity begins.
COMPRESS THRESHOLD
Sets the level above which the compressor/ limiters’ activity begins.
COMPRESSION RATIO
Sets the compressor/ limiter’s ratio from 1.4:1 to 20:1.
BYPASS
Enables/disables the compressor/limiter/ expander.
2.9 Parametric Equalizer/Notch Filter Controls
CUT/BOOST
Adjusts the cut or boost from -30dB to +15dB.
BANDWIDTH
Sets the selectivity (”Q”) of the equalizer, and therefore the amount of the
spectrum affected by the CUT/BOOST control. Calibrated in octaves, from .05 to
3.3 (see Section 1.12, Paramteric Equa1izer/Notch Filter).
FREQUENCY
Determines which frequency lies at the center of the bell-shaped curve that
encompasses the particular frequencies affected by this band of the equalizer.
Calibrated in Hz, the LO,” ”MID'* and *’HI” sections may be overlapped.
EQ BYPASS
Switches the parametric equalizer/notch filter into or out of the circuit path.
2.10 Output Gain Control, Metering
OUTPUT GAIN
Sets the overall gain of the 528 from aminimum of -15dB, to OdB (unity) at top
dead center, to amaximum of +15dB.
OUTPUT LE¥HL
Indicates the unit’s output level in volume units (VU). OVU =1.23 volts across
600 ohms (+4dBm).
CLIP
Illuminates when output levels are within 3dB of the onset of clipping.
GAIN REDUCTION
Indicates the gain reduction provided by either the dynamic range processor
section (compressor/limiter/ expander), or by the de-esser section.
COMPIESS/DE-ESS
Switche sthe GAIN REDUCTION meter to read the gain change at the dynamic
range processor’s VCA, or the de~esser’s VGA.
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2.11 Installation
The unit is designed for mounting in astandard 19** rack, and requires only 1
rack space (1-3/4**). The 528*s INPUTs. OUTPUTS and SIDECHAIN connectors
should be wired to apatch bay (like the Symetrix Patch 32) for ease of
operation. Asuggested arrangement is shown in Figure 2.3. The patching
output/ input connections and the SIDECHAIN output/input connection must remain
intact when not used. When the unit is wired into apatch bay, these
connections must be normalled.
CAUTION
Do not mount the 528 near hi§h power devices like amplifiers and
power supplies. When the unit is rack mounted, take care to keep it as
far from hum fields as possible. Like all devices designed to provide
hi^h §ain for low level signals, the 528'smicrophone preamp is
sensitive to induced hum.
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