Symetrix 258E User Manual

528E Voice Processor

User’ s Guide

528E

Table of Contents

Chapter 1 Introduction 1
Chapter 2 Operator Safety Summary 2
Chapter 3 Fast Setup 3
Chapter 4 Front Panel Overview 4
Chapter 5 Rear Panel Overview 8
Chapter 6 Voice Processing Tutorial 10
Chapter 7 Using the 528E 20
Chapter 8 Applications 28
Chapter 9 Technical Tutorial 32
Chapter 10 Troubleshooting 36
Chapter 11 Specifications 37
Chapter 12 Warranty & Service 39
Appendix A Disassembly Instructions 41

and Output Level Switch

Appendix B Declaration of Conformity 42

© April 2000-01 Symetrix, Inc.
All rights reserved.

Symetrix Part Number 53528-0E00
The information in this guide is subject to

change without notice. Symetrix, Inc. shall not
be liable for technical or editorial errors or
omissions contained herein; nor is it liable for
incidental or consequential damages resulting
from the furnishing, performance, or use of this
material.

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 user guide
may be reproduced or transmitted in any form or

528E

by any means, electronic or mechanical, without
permission in writing from Symetrix, Inc. If,
however, your only means of access is elec­tronic, permission to print one copy is hereby
granted.

Mountlake Terrace, WA 98043 USA

6408 216th St. SW
Tel [phone]

Fax [phone]

www.symetrixaudio.com

IntroductionChapter 1

The Symetrix 528E is a single-channel Voice Processor intended for use in voice-over studios,
broadcast studios, sound-reinforcement, music and speech recording, and post-production. Simply
stated, the 528E consists of a high-quality microphone preamp coupled to a three-band parametric
equalizer, a de-esser, and a dynamic range processor. It is everything you would have at your
disposal in a world-class mixing console. The 528E accepts both mic and line inputs. Of course,
while we use the term “Voice Processor” for the 528E, it is perfectly at home with any signal,
vocal or not.

The microphone input uses a balanced-transformerless design using an integrated circuit specifi­cally developed for this application. The 528E’s microphone input works with any phantom­powered condenser microphone or any low-impedance microphone having a balanced, floating
output. The line input uses a balanced transformerless design. The line input’s design uses matched
resistors to attain a high, wideband, CMRR (common-mode rejection ratio) and multistage RFI
filters to prevent Radio Frequency interference problems.

The de-esser operates by selectively removing the high frequencies from the input signal when
sibilant sounds are present and exceed the threshold level. The filter frequency can be varied over a
wide range to accommodate different speakers and languages.

The dynamic range processor combines an interactive compressor/limiter and a downward ex­pander. Typically, the downward expander helps reduce studio noise as well as the artifacts of
close miking. The compressor/limiter gives you overall control over the dynamic range of the
output signal and helps maintain a high overall signal level. The three-band parametric equalizer is
a reciprocal-curve design. An unusual leapfrog topology minimizes the number of amplifiers in the
signal path while ensuring that each frequency band interacts with its neighbor in a desirable and
musical fashion.

The 528E’s output section can drive balanced loads at line or mic levels. A line-level unbalanced
output is also provided. For broadcast applications, a switchable voice symmetry circuit helps
make speech waveforms more symmetrical, which makes better use of the transmitter’s output
power.

Each of the dynamics processors have individual six-segment LED displays and an eight-segment
display monitors the overall output level. All inputs and outputs are available via XLR connectors
and the connection points between the individual processors can be accessed via TRS phone jacks.
The interstage patching may be used to change the insertion order of the processors or to insert
additional processing.

We recommend that you read this manual from cover to cover. Somewhere between the confines of
the two covers you should find the answers to most (98%) of your questions, both technical as well
as musical. Should you have any comments or questions, please do not hesitate to contact us at the
numbers/addresses below. Your calls are always welcome.

Phone: [phone]
Fax: [phone]
Email: [e-mail]
Web site: www.symetrixaudio.com

COMPRESSOR (-dB)

9

3916 12 620

EXP/COMP

IN

COMP RATIOCOMP THRESEXP THRES

OUT

528

VOICE
PROCESSOR

MIC
LINE

-15 PAD
NORM

MIC PRE-AMP

CLIP

20

MIC GAIN(dB)

PHANTOM

15

3K

DE-ESS (-dB)

12 9 6 4 2

8K60800

DOWNWARD EXPANDER (-dB)

1620 12

-15

DE-ESS

BYPASS

0

-30 -15

IN

THRESHOLDFREQUENCY

OUT

Front panel

15 WATTS MAXIMUM

MANUFACTURED IN THE USA BY

THIS UNIT CONTAINS NO

USER SERVICEABLE PARTS.

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

RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.

BALANCED OUTPUT

POWER

OUTPUT STAGE

UNBALANCED

OUTPUT INPUT

Rear panel

LOW EQ HIGH EQ

1.5160263-10 -25

4500 .3

16101+20 0 -40

EQUALIZER

OUTPUT

INPUT

MID EQ

EXPANDER/COMPRESSOR

SIDECHAIN

TIP=RETURN
RING=SEND

INPUTOUTPUT

OUTPUT

DE-ESS

PRE-AMP

STAGE

INPUT OUTPUT

OUTPUT LEVEL (VU)

-15 -20 -10 -6 -3

EQ

IN
OUT

0

-15 +15

GAIN (dB)

MIC INPUT

0 3 CLIP

VOICE

SYMMETRY

IN

POWER

OUT

PHANTOM

POWER

+48V
BYPASS

528E

dBOCTHzdBOCTHzOCTHz dB

01.56.8K01.52.5K0

+15 -15 4.322K6804 -15 .3160+15 6.3K +15

CUT/BOOSTBANDWIDTHFREQUENCYCUT/BOOSTBANDWIDTHFREQUENCYCUT/BOOSTBANDWIDTHFREQUENCY

LINE INPUT

1

Operator Safety Summary Chapter 2

.

Equipment Markings

WARNING:

AVIS:

SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.

No 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 uninsulated “dangerous voltage” within
the product's enclosure that may be of sufficient
magnitude to constitute a risk of electric shock to
persons. The exclamation point within an equilateral
triangle is intended to alert the user of the presence of
important operating and maintenance (servicing)
instructions in the literature accompanying the product
(i.e. this manual).

Caution To prevent electric shock, do not use the

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

Terms

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

These are:

Note Identifies information that needs

Caution Identifies information that, if not

Warning Identifies information that, if

CAPITALS Controls, switches or other markings

Boldface Strong emphasis.

Important Safety Instructions

Please read and keep these instructions. Heed and
follow all warnings and instructions. Install in
accordance with the manufacturer’s instructions.

Power Source This product is intended to operate
from a power source that does not apply more than
250 V rms between the power supply conductors or

528E

between either power supply conductor and ground.
A protective ground connection, by way of the
grounding conductor in the power cord, is essential

2

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

TO REDUCE THE RISK OF FIRE OR
ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE

RISQUE DE CHOC ELECTRIQUE
NE PAS OUVRIR

S’adresser a un reparateur compétent.

extra emphasis. A Note generally
supplies extra information to help
you to better use the 528E.

heeded, may cause damage to the
528E or other equipment in your
system.

ignored, may be hazardous to your
health or that of others.

on the 528E’s chassis.

for safe operation.

Grounding The chassis of this product is grounded

through the grounding conductor of the power cord.
To avoid electric shock, plug the power cord into a
properly wired receptacle before making any
connections to the product. A protective ground
connection, by way of the grounding conductor in the
power cord, is essential for safe operation. Do not
defeat the safety purpose of the grounding plug.
The grounding plug has two blades and a third
grounding prong. The third prong is provided for your
safety. When the provided plug does not fit your
outlet, consult an electrician for replacement of the
obsolete outlet.

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 cord and
connector specified for the product and your operating
locale. Use only a cord that is in good condition.

Protect the power cord from being walked on or
pinched, particularly at plugs, convenience recep­tacles, and the point where they exit from the
apparatus.

Phantom Power To prevent hazard or damage
ensure that only microphone cables and microphones
designed to IEC-268-15A are connected.

Proper Fuse The user accessible fuse is a part of the
IEC AC inlet connector. The fuseholder accepts 5 x
20 mm diameter fuses. For 117 VAC operation, the
correct value is 0.25A, 250 VAC, standard. For 230
VAC operation, the correct value is 0.125A, 250
VAC, standard.

Operating Location 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. Do not install near any heat source
such as radiators, heat registers, stoves, or other
apparatus (including amplifiers) that produce heat.
Unplug this apparatus during lightning storms or
when unused for long periods of time.

Stay Out of the Box To avoid personal injury (or
worse), do not remove the product covers or panels.
Do not operate the product without the covers and
panels properly installed. Only use accessories
specified by the manufacturer. Clean only with a
damp cloth.

User-serviceable parts There are no user serviceable
parts inside the 528E. In case of failure, refer all
servicing to the factory. Servicing is required when
the 528E has been damaged in any way, such as when
a power supply cord or plug is damaged, liquid has
been spilled or objects have fallen into the apparatus,
the apparatus has been exposed to rain or moisture,
does not operate normally, or has been dropped.

Chapter 3

Fast Setup

Fast Setup

Follow these instructions to get your 528E up-and-running as quickly as possible. The intent of this
section is fast setup. If you need something clarified, then you’ll find the answer elsewhere in this
manual.

Connections

Connect your input source to the appropriate XLR connector. Connect the 528E’s output to line-level
input using the XLR output connector. If you need to feed a mic-level input, refer to Appendix A before
proceeding further. Ignore the interstage patching for now (details in Chapter 7 and 8).

If you are using a condenser microphone, refer to “Phantom Powering Condenser Microphones” in
Chapter 9 before depressing the PHANTOM POWER switch.

Caution Failure to connect the 528E to the proper AC mains voltage may cause fire and/or

internal damage. There are no user serviceable parts inside the chassis. Refer all
service to qualified service personnel or to the factory.

Warning Lethal voltages are present inside the chassis. There are no user serviceable

parts inside the chassis. Refer all service to qualified service personnel or to the
factory.

Connect the AC input to an AC power source of the proper voltage and frequency, as marked on the
rear of the unit.

Settings

Set the controls and switches on the front and rear panel as follows:

lenaPtnorF

lortnoC

ENIL/CIM.dqersa

DAPBD51-TUO

NIAGCIMkcolc'o00:21

ressEeD

YCNEUQERF

ssE-eD

DLOHSERHT

TUO/NISSE-EDNI

rednapxE

DLOHSERHT

rosserpmoC

dlohserhT

gnitteS

woLQE

woLQE

woLQE

kcolc'o00:21

)WCxam(0

)WCxam(0

)kcolc'o00:21(01-

diMQE

diMQE

diMQE

hgiHQE

hgiHQE

lenaPtnorF

lortnoC

YCNEUQERF

HTDIWDNAB

TSOOB/TUC

YCNEUQERF

HTDIWDNAB

TSOOB/TUC

YCNEUQERF

HTDIWDNAB

gnitteS

)kcolc'o00:21(0

sevatco5.1

)kcolc'o00:21(0

kcolc'o00:21

sevatco5.1

kcolc'o00:21

kcolc'o00:11

sevatco5.1

OITARrosserpmoC)kcolc'o00:21(1:2

hctiwsPMOC/PXENITUO/NIQE

ECIOV

YRTEMMYS

hctiws

TUONIAG

hgiHQE

TSOOB/TUC

NI

)kcolc'o00:21(0

)kcolc'o00:21(0

3

528E

Initial Setup

The 528E’s controls and switches are now set according
to the preceding section. All connections listed in
Section 6.1 are now made. The 528E should now pass
signal. The OUTPUT LEVEL LED display and the POWER
LED should be illuminated. Depending upon the signal
levels, the compressor’s gain-reduction display may be
illuminated.

tuptuO

tupnIeniL

lenaPraeRgnitteS

fotupniottcennoC

,redrocerepat,elosnoc

.cte

level-eniltcennoC

.erehecruos

Refining Your Settings

At this point, the 528E should pass signal. There should
be some activity on some of the LED displays.

Mic Preamp Gain

Temporarily put the De-ess, Exp/Comp, and EQ sections into bypass mode, set the MIC GAIN
control so that the OUTPUT LED display indicates a signal level between -10 and 0 VU. The CLIP
LED should almost never illuminate.

De-Esser Settings

Use the de-esser to reduce the level of sibilant sounds (S and T sounds) if they are objectionable.
Set the THRESHOLD control so that the de-esser gain-reduction display shows about 12 dB of gain­reduction. Now “tune” the FREQUENCY control for maximum sibilance reduction. Finally, reduce the
setting of the THRESHOLD control until you reduce the sibilance to a tolerable level. Try to use the
lowest setting of the FREQUENCY control that gets the job done.

Downward Expander Settings

Use the downward expander to reduce room noise and/or mouth noises. Set the THRESHOLD control
to allow low level speech sounds to pass while still blocking the room sound.

Compressor Settings

Use the threshold control to vary the amount of gain reduction, as indicated on the compressor’s
gain-reduction display. Generally, 3 to 6 dB is sufficient, unless you are using a low compression
ratio (below 2:1), or you want a special effect. Pick a ratio suited to the task at hand: low ratios
and low thresholds for unobtrusive level control, medium ratios for overall level control and
consistency, high ratios (> 8:1) for limiting or in-your-face sorts of sounds.

tupnIciM

motnahP

rewoP

.ereh

enohporcimtcennoC

seriuqercimfisserpeD

.gnirewopmotnahp

Equalizer Settings

The settings given will work well with male voices. For women, the low-EQ range shifts up to 200
or 300Hz, the mid-EQ range shifts up to 3-5 kHz.

If you are using a microphone that exhibits proximity effect when you close-talk it, then you’ll
probably need to reduce (cut) the bass (low) response somewhat. 3-6 dB should be fine (don’t do
this if you want a big, ballsy sound). A bit of mid-EQ will help make voices cut and seem loud.
The high-EQ adds brightness and intimacy.

If you are using a microphone that has no proximity effect (like the ElectroVoice RE-20), then
you’ll probably need to increase (boost) the bass response somewhat. 3 to 6 dB should do the job.
The same mid- and high- EQ recommendations given previously still apply. A thorough discussion
of equalization may be found in Chapter 6.

528E

4

Output Settings

For many applications, setting the output GAIN control at 0 dB (12:00 o’clock) works fine. If you
are adding a bunch of EQ (which tends to cause an overall level increase), then you may need to
decrease the GAIN setting. On the other hand, if you are using a fair amount of compression, you
may need to add some gain to compensate for the level lost in compression. Pick a setting that
gives you enough signal downstream, yet still keeps the CLIP LED from illuminating. The output
display is peak responding, so you can’t quite set levels as if it were a VU meter.

The output CLIP LED monitors both the equalizer and the output stage. Large amounts of boost
and/or high signal levels can cause CLIP indications. If this occurs, lower the signal level via the
GAIN control. It is also possible for the output stage to clip if a processor, inserted via the output
stage access jacks, is contributing gain to the overall signal path. In this case, either lower the gain
of the insert processor or reduce the setting of the GAIN control.

528E

5

Mic Preamp

COMPRESSOR (-dB)

3916 12 620

COMP RATIOCOMP THRESEXP THRES

IN
OUT

DOWNWARD EXPANDER (-dB)

2

63

-10 -25

1620 12

9

EXP/COMP

101+20 0 -40

BYPASS

Chapter 4Front Panel Overview

MIC/LINE Selects between the Mic input (switch in) and

Switch Line input (switch out).

-15 dB PAD Inserts 15 dB pad for strong mic signals.
Switch

MIC GAIN Sets the gain of the mic preamp for best compro-

mise between signal-to-noise ratio and headroom.

CLIP LED Monitors inputs (mic and line) for clipping.

Illuminates 3 dB below the actual clip point.

PHANTOM Illuminates when 48V phantom power is present at the

microphone input connector. LED The phantom
power switch is located on the rear panel.

DE-Esser

FREQUENCY Sets the rolloff (cutoff) frequency of

the de-esser.

THRESHOLD Sets the threshold level for the de-esser.

Signals above this level cause de-esser
action, signals below do not.

IN/OUT Switch Hard-wire bypasses the de-esser. The

de-esser is active when this switch is in.

LED Display Indicates the amount of de-esser

activity at any instant in time.

M

DE-ESS (-dB)

12 9 6 4 2

15

3K

8K800

MIC PRE-AMP

MIC
LINE

-15 PAD
NORM

-15

-30

THRESHOLDFREQUENCY

PHANTOM

CLIP

6020

MIC GAIN(dB)

DE-ESS

0

IN
OUT

Downward Expander / Compressor

EXP THRESH Sets the threshold level

for the downward
expander. Signalsbelow
this threshold are
downward expanded
(reduced in level).

COMP THRESH Sets the threshold level

for the compressor.
Signals above this
threshold cause gain
reduction in the

compressor.
COMP RATIO Sets the compression ratio of the compressor.
EXP/COMP Defeats the downward expander / compressor. This is not a hard-wire bypass.

IN/OUT Switch
DOWNWARD Indicates the amount of downward expander activity (gain reduction) at any

EXPANDER instant in time.
LED Display

COMPRESSOR Indicates the amount of compressor activity (gain reduction) at any instant in
LED Display time.

528E

6

Parametric EQ Low

0

FREQUENCY Varies the center frequency of the

low-frequency equalizer from
16Hz to 500 Hz.

BANDWIDTH Varies the bandwidth of the low-

frequency equalizer from 0.3 to 4
octaves. (Q=4.8 to 0.27).

CUT/BOOST Sets the degree of boost or cut;

±15 dB.

Parametric EQ Mid

FREQUENCY Varies the center frequency

of the mid-frequency eq from
160 Hz to 6300 Hz.

BANDWIDTH Varies the bandwidth of the

mid-frequency eq from 0.3
to 4 octaves. (Q=4.8 to 0.27).

CUT/BOOST Sets the degree of boost or

cut; ±15 dB.

Parametric EQ High

FREQUENCY Varies the center frequency

of the equalizer from
680 Hz to 22 kHz.

BANDWIDTH Varies the bandwidth of the

high-frequency equalizer
from 0.3 to 4 octaves.
(Q=4.8 to 0.27).

HIGH EQ

LOW EQ

OCTHz dB

1.5160

4500 .316 -15

MID EQ

4 -15 .3160 6.3K +15

dBOCTHz

01.56.8K

0

+15

CUT/BOOSTBANDWIDTHFREQUENCY

dBOCTHz

01.52.5K

CUT/BOOSTBANDWIDTHFREQUENCY

-2

EQ

CUT/BOOST Sets the degree of boost or

cut; ±15 dB.

IN/OUT Switch Hard-wire bypasses the

entire equalizer.

+15 -15 4.322K680

CUT/BOOSTBANDWIDTHFREQUENCY

Output Section

GAIN Sets the overall gain of the 528E’s output over

a ±15 dB range. Note: the actual adjustment
point is in the expander/compressor's VCA,
which is pre-EQ.

VOICE Inserts speech waveform asymmetry
SYMMETRY correction into the signal path.

OUTPUT LED Indicates the peak output level of the 528E

relative to the balanced output. 0 VU
Display on the display corresponds to
+4dBu at the balanced output. For
unbalanced applications, the actual output
level is 6 dB lower than that shown by the display.

Note If the internal mic-level output switch has been depressed, the output level is

-40 dBu when the display indicates 0 VU.

POWER LED Indicates the presence of AC power.

OUTPUT LEVEL (VU)

-15 -20 -10 -6 -3

0

-15 +15

GAIN (dB)

0 3 CLIP

SYMMETRY

VOICE

IN
OUT

IN
OUT

POWER

528E

7

Rear Panel Overview Chapter 5

E

UNBALANCED

OUTPUT INPUT

OUTPUT STAGE

BALANCED OUTPUT

.
.

15 WATTS MAXIMUM

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

SERIAL NUMBER Note for your records.

OWER INPUT IEC-power connector. Connect only to appropriate AC power source. Refer to

AC P

rear-panel marking for correct AC source voltage.

RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.

MANUFACTURED IN THE USA BY

THIS UNIT CONTAINS NO

USER SERVICEABLE PARTS.

POWER

OUTPUT STAGE

BALANCED XLR-male. Balanced, line-level
OUTPUT output. This output may be

converted to mic-level via an
internal switch. Refer to

Appendix C.
UNBALANCED TRS phone jack (wired for
OUTPUT unbalanced operation) This is the

unbalanced, line-level output of

the 528E. This jack is unaffected

by the internal switch (see

preceding paragraph).

BALANC

528E

OUTPUT TRS phone jack (wired for unbalanced operation). This is the input to the output
STAGE stage and interrupts the signal coming from the remainder of the 528E.
INPUT

Equalizer

OUTPUT TRS phone jack (wired unbalanced). This is the

output of the equalizer. This jack does not interrupt

the signal flow to the 528E’s output stage.
INPUT TRS phone jack (wired unbalanced). This is the

input to the equalizer. This jack interrupts the

signal from the Expander/Compressor.

EQUALIZER

OUTPUT INPUT

EXPANDER/COMPRESSOR

OUTPUT TRS phone jack (wired unbalanced).

This is the output of the Expander/

Compressor. This jack does not

interrupt the signal flow to the 528E’s

equalizer.
SIDECHAIN TRS phone jack wired as an insert jack

(Tip=return, Ring=send). Use this jack

to access the compressor/expander’s

sidechain.

EXPANDER/COMPRESSOR

OUTPUT

SIDECHAIN

TIP=RETURN

RING=SEND

INPUT

8

INPUT TRS phone jack (wired unbalanced). This is the input to the Expander/

P

Compressor. This jack interrupts the signal from the De-Esser.

De-Ess

OUTPUT TRS phone jack (wired unbalanced). This is the

output of the De-Esser. This jack does not
interrupt the signal flow to the 528E’s Expander/
Compressor.

DE-ESS

INPUT TRS phone jack (wired unbalanced). This is the

input to the De-Esser. This jack interrupts the
signal from the Mic/Line inputs.

Preamp

LINE INPUT

PRE-AMP

STAGE

OUTPUT

PREAMP STAGE TRS phone jack (wired unbalanced). This is the output of the Mic/Linepreamp.
OUTPUT This jack does not interrupt the signal flow to the 528E’s De-Esser.

LINE INPUT XLR Connector. 10-kilohm balanced bridging line input intended for

signals ranging from -10 dBu to +4 dBu.

MIC INPUT XLR connector. Balanced input suitable for low-impedance microphones.

48V phantom powering available.

OUTPUT

MIC INPUT

INPUT

PHANTOM

POWER

+48V
BYPASS

PHANTOM POWER Pushbutton switch enabling Phantom Power on Mic Input.

528E

9

Voice Processing Tutorial

Basics

The Symetrix 528E Voice Processor combines Symetrix’ program controlled interactive dynamic
range processing technique with a three-band parametric equalizer. This combination of processors
is similar to a voiceover or vocal signal processing chain as used in a recording or voiceover
studio. “Program controlled” means the 528E’s dynamic range processor section analyzes incom­ing signals, then adjusts its release time to match the transient characteristics of those signals.

This chapter of the manual contains a tutorial on the basics of dynamic range processing and
equalization: the two key ingredients in the 528E. The tutorial information is intended to provide a
background for the information found in the remainder of this manual.

Dynamic Range Processing

Dynamic range processors are used to fit wide-range signals into narrow-range transmission or storage
channels. The dynamic range of acoustical signals found in real life usually 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 a 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 which prevents “pumping” and “breathing” even when high ratio compression
is necessary. Because the compressor/limiter and the downward expander are interactive, the 528E
always responds appropriately, while providing automatic control over a wide range of input
levels.

Chapter 6

Strictly speaking, the terms compressor and limiter refer to two different devices. Oftentimes the
two are combined into a single device called a compressor/limiter. Compressor/limiters usually
perform as either a compressor or a limiter, but not both at once. Functionally, a compressor/
limiter is a device 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.

In addition to their roles as remedial signal processors, compressors also have a creative role. You
can use a compressor to increase the apparent sustain of a guitar, increase apparent loudness,
improve the consistency of a bass by removing or reducing level changes, and many other things.
Generally speaking, the settings for these applications are somewhat extreme, so experimentation is
the name of the game.

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 distinctly different uses:

1. To describe the actual range of signal fluctuations that are going through the equipment.

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).

Dynamic Range as a Specification

The maximum usable range of operation for a particular 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.

528E

Noise floor is defined as the lower limit of a circuit’s operating level, and is a function of its self-

10

generated electrical noise. Very noisy circuits have a high noise floor, quiet circuits have a low
noise floor. All circuits have a noise floor, unless they are operating at -460 degrees Fahrenheit
(absolute zero). The maximum output level of a circuit is the upper limit of the operating level,
and is the level at which clipping begins and is a function of the internal power supply voltage. To
put levels in perspective they must be referenced to some nominal operating level, like 0 dBm.
That’s why noise specs are stated as negative numbers.

In the case of the 528E, noise is referred to the input, and stated as equivalent input noise (EIN).
The noise specification is given this way because the gain of the 528E’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 0 dBm output, algebraically add the preamp gain to
the EIN.1

Since maximum output level is usually greater than 0 dBm, it’s stated as plus something. The
528E’s maximum output level is +18 dBm into a 600-ohm balanced load, which is 18 dB above 0
dBm. The difference between the noise floor and the onset of clipping is the dynamic range. To
find the 528E’s dynamic range with 50 dB preamp gain, subtract -89 from 18. The result (113 dB)
is the dynamic range.

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 a whisper to a
shout, is well over 100 dB. Thus, the microphone converts the sound pressure of a voice going
from a whisper to a shout into an electrical output signal having the same dynamic range.

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 80 dB, while digital
recorders top out at around 96 dB. As good as these machines are, there’s still not quite enough
room for very wide dynamic range signals. In order to maintain a 60 dB signal-to-noise ratio (to
keep the signals 60 dB above the noise floor), the dynamic range of signals stored on the analog
tape machine would have to be restricted by 20 dB, while the digital recorder would be restricted
by 36 dB.

A compressor or limiter is often used to reduce 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 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, increasing the amount of change at the
lower end of the dynamic range with a downward expander or gate.

Compressors are to Downward Expanders as Limiters are to Gates

Compressors reduce the dynamic range of their output whenever the input signal is above thresh­old, while downward 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, the ratio of the input level to the output level, which
is generally user-adjustable. 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 usually have a nonadjustable ratio that is very high (greater than 10:1). At 10:1, the limiter

528E

11

allows only a 1 dB increase in the output level for every 10 dB 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.

The Threshold Concept

The threshold is the level at which a dynamic range processor’s activity begins. In operation, the
dynamic range processor’s sensing circuitry constantly “looks at” the incoming signal and com­pares it to a reference level, which is called the threshold level. In practice that reference level is
set by the operator via the threshold control. Remember, compressors and limiters respond when
signals at the input are above threshold, while downward expanders and gates respond only when
signals at the input are lower than the defined threshold.

The VCA - Voltage Controlled Amplifier

The action of any dynamic range processor depends on some method of changing the gain based
on some external signal. Typically this takes the form of a special sort of amplifier whose gain is
controlled by a DC voltage. That part of the circuit is called a voltage controlled amplifier, or
VCA. Inside the 528E a separate buffered audio signal is sent to a group of circuits that comprise
the detector (envelope follower to you synthesists). The detector circuits turn the AC audio signal
into a DC control voltage, which is sent to the VCA under the direction of the front panel controls.

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. In the real world, linear expanders aren’t too practical because clipping occurs when signals
just below maximum output level are expanded.

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 is passed 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.
However, that signal would be 1 dB 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 a downward 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.

Note: in the interests of clarity and brevity, the term expander will be defined as a downward
expander from this point forward in this manual.

How Expanders Increase Usable Dynamic Range

The lower limit restriction of a system is the noise floor, which is usually well below the 528E’s
lowest expander threshold (-50 dBu). 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 dynamic range of all signals below threshold. This action increases the apparent
loudness of signals, while decreasing the apparent loudness of the noise.

For example, an expander operating at a ratio of 1:2 will cause 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

528E

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 20 dB by the action of expander, which is responding to

12

a 10 dB drop in the signal with its 1:2 ratio.

De-essers

A de-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 overemphasized especially when the talker is close-miked.

Many sibilant vocal sounds like “s,” “sh,” and “t” are very difficult to reproduce electronically,
because they contain a large percentage of very high frequency harmonics. But because these
sounds are 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 (3 kHz to 8 kHz), 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 528E’s de-esser controls excessive sibilant and fricative vocal sounds, which can often be as
much as 12 dB louder than the rest of the spectrum. It’s activity is similar to a frequency conscious
compressor/limiter (with an equalizer boosting the high frequencies in the sidechain). Unlike a
compressor/limiter however, the de-esser operates only on the frequencies selected and above.
Unlike an equalizer, the de-esser can reduce the offending sounds without sacrificing intelligibility,
because it operates dynamically, removing only sounds that are disproportionately loud, and only
those that fall within the operator-selected control range.

De-essers usually include controls that allow the operator to determine which frequencies are
controlled, and how much those frequencies are actually attenuated. The 528E’s de-esser controls
are frequency, which is variable from 800 Hz to 8 kHz, and threshold, which may be set from 0 dB
to -30 dB. In other words, the 528E’s de-esser will attenuate selected frequencies between 800 Hz
and 8 kHz as much as 20 dB.

Sidechain Processing

The sidechain is a patch point in the control circuit of a dynamic range processor, which provides
access to the part of the circuitry that tells the VCA what to do. The 528E’s sidechain routes
through a rear panel TRS jack that allows the control signal to be processed outside the unit (see
Figure 7-6 for specific hookup information).

Refer to the block diagram in Figure 7-1. Notice the sidechain connections that come from the
compressor/limiter/expander section. They allow access to the audio input of the control circuit (a
fancy envelope follower by any other name) for the dynamic range processor. 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 528E without actually processing the signal that’s going through the
VCA (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 connections is to make the action of the 528E’s dynamics processor
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 VCA 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 VCA
prevents those frequencies from being used to create gain changes. Applications utilizing the
sidechain may be found in Chapter 8.

528E

13

Equalization

Equalization is one of the most powerful tools available to the audio engineer. It is, quite possibly,
the first signal modification device that most people experience (aside from the volume control).
This experience takes the form of using the tone controls found on most consumer audio equip­ment. Even in this primitive form, simple tone controls can shape and alter a sound, giving us
pleasure or pain, evoking emotion, or simply enhancing our listening pleasure.

The parametric EQ in the 528E provides both creative and corrective frequency shaping - it can be
used to create a more pleasing sound, and to correct frequency response problems. The equalizer
has a symmetrical ±15 dB boost/cut response.

The term “parametric” simply refers to the fact that the primary operating parameters of the
equalizer may be altered by the user. The user adjustable parameters are:

• center frequency (or fc, expressed in Hz),

• bandwidth (sometimes called “Q,” or selectivity, expressed in octaves), and

• the amount of cut or boost (expressed indB).

These terms are defined as follows:

1. Center Frequency is defined as the frequency (in Hz) of the middle of the bell shaped response

curve formed by a filter.

2. Bandwidth is the width of the bell shaped curve, measured between its -3 dB 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.

Equalization Tutorial

Equalization is nothing more than selectively (or not) amplifying a signal based on frequency.
Since audio signals consist of combinations of fundamental signals and their harmonics, changing
the tonality or the spectral balance of a signal involves nothing more than altering the relationship
of the fundamental to its harmonics, and of the harmonics to themselves. Each harmonic is
responsible for 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.

The audio spectrum has several critical portions that are responsible for our perceptions of sounds
that we hear:

Range Frequencies Musical Location

Very Low Bass 16-64 Hz 1st and 2nd octaves.
Bass 64-256 Hz 3rd and 4th octaves.
Midrange 256-2048 Hz 5th, 6th, and 7th octaves.
“Lisping” Quality 3000 Hz Between the 7th and 8th octaves.
Presence Range 4750-5000 Hz Between the 8th and 9th octaves.
Brilliance 6500-16 kHz Part of the 9th through the 10th

Power and Fullness

2

octave.

In the very low bass region lies the threshold of feeling, where the lowest sounds, like wind, room
effects, and distant thunder, are felt, rather than heard. In the upper half of the first octave of this
range, research has shown that the fundamentals of piano, organ and even the harp reach well into

528E

this range. Harvey Fletcher (of Fletcher-Munson fame) charted the sensitivity of the ear for various

14

parts of the spectrum at levels that are lower than those of reality. Fletcher’s compensation curves
(the well known Fletcher-Munson curves) show that for equal loudness in this range at lower
recorded and reproduced levels shows requirements for tremendous boosts, on the order of 10 to
30 dB. Aside from the subjective effects of this range, the ability to control unwanted sounds in
this range is equally important to subdue stage rumble and outside traffic noise (especially impor­tant where there are subways beneath buildings!). Overemphasis caused by close cardioid micro­phone placement can cause muddiness in the overall sound; attenuating (cutting) the very-low-bass
region can greatly improve overall clarity.

Rhythm and Musical Foundation

In the bass region, most of the low, grave tones of the drum and piano can be found. Here we can
also find the fundamentals of the rhythm section, as well as the foundation of all musical structure.

It was Leopold Stowkowski who said “If I had a thousand bass viols I could use them all!” This is
not as extreme as it may sound. A bass viol, even though it is reinforced by its sounding board,
generally plays single notes and possesses little dynamic range. In a large orchestra, as many as
eight bass viols may be used. A total of 1000 bass viols in this case would only give an additional
21 dB of level, which is not an inordinate amount given a glance at Mr. Fletcher’s equal loudness
curves. Pay attention to this range because the overall musical balance of your program can be
controlled by equalizing or attenuating the 100 Hz range.

Telephone Quality

The ear is reasonably sensitive in the midrange frequencies, and sound restricted to this range has a
telephone-like quality (which is generally why telephone-quality frequency response covers the
300-3 kHz range).

If you make the 6th octave (500-1024 Hz) louder with respect to the other octaves, the subjective
result is a horn-like quality. If you emphasize the 7th octave (1000-2000 Hz), the effect is one of
tinniness.

The fundamental tones in most music lie equally above and below middle C (261 Hz), from 128 to
512 Hz. As most instruments are rich in the first overtones, the majority of sound energy is found
up to the 2.5 kHz range. Music editors and others engaged in listening to music over long periods
find that listening fatigue can be reduced by attenuating the 5th, 6th, and 7th octaves by about 5 dB.

Lisping Quality

The 3 kHz range delivers a generous stimulus to the ear. At very loud levels the region of greatest
ear sensitivity shifts downward from 5 kHz; this is why many “PA” speakers have broad peaks in
this region. A characteristic of low-level signals peaked at 3 kHz is a “lisping” quality, and the
total inability to distinguish labial sounds such as m, b, and v.

In wide-range lower level systems, a peak in the 3 kHz region has a masking effect on important
recognition sounds, and on others which lie above 4 kHz. Brilliance and clarity are lost and
without attenuation of this region, an unconscious strain with increasing fatigue is felt according to
the amount of 3 kHz boost.

Presence Range

The usual band affecting clarity in male speech is 3000 to 6000 Hz. In a woman’s voice, the
fundamentals are roughly an octave higher than a man’s, and a woman’s range of consonant clarity
lies between 5000 and 8000 Hz (the high-end of this range approaches a region of hearing insensi­tivity in humans). Furthermore, the total range of a woman’s voice is about half that of a mans,
stimulating fewer hearing nerves, and for this reason, is consequently still weaker upon reception.

Wide range sounds, especially those of singing voices, have fundamentals with harmonics in the 5
kHz region of good ear sensitivity. Voices that are powerful or rich with harmonics at 5 kHz sound
especially pleasing, clear and full. Male opera singers are particularly favored with 5 kHz sounds,

528E

15

women less so. In popular music, this range shifts downward somewhat. It follows that voices
deficient in the 5 kHz range can be enhanced in listening value by a generous boost on the order of
5 to 8 dB at 5 kHz. A secondary benefit of this boost is an apparent increase in level; a 6 dB rise at
5 kHz frequently gives an apparent increase of 3 dB to the overall signal.

Attenuating the 5 kHz range on instruments gives a “transparent” quality to the sound, providing,
of course, that the remainder of the signal is otherwise wide range. Microphones having a dip in
this region lack the “punch” or “presence” to which we (Americans) are accustomed.

Brilliance

Unvoiced consonants attributed to tooth, tongue and lip sounds are high in frequency, and reach
the 10 kHz range. These frequencies account for some clarity and most brilliance, even though
they contain less than 2% of the total speech energy. This also holds true for musical instruments;
especially percussion. Boosting or cutting this range affects clarity and naturalness. In speech, the
9th and 10th octaves impart intimacy although too much emphasis can make secondary speech
sounds (lip smacking, etc.) objectionable (a good case for a expander).

Some microphones having a rise at the higher frequencies (especially omni microphones) benefit
from some attenuation in this region. Those microphones having under damped diaphragms may
ring at these frequencies, causing an annoying sibilant distortion on speech. On musical forms
using hand percussion, boosting this range frequently results in an astonishing and pleasing feeling
of clarity.

Conclusions

When the article containing the above excerpts was written (probably around 1963), stereo was
just becoming a commercial reality (you could still purchase mono and stereo versions of an LP
and there were still more FM stations broadcasting in mono than stereo), and as many mixers
contained rotary mix pots as those that used slide pots. The value of individual channel equaliza­tion was known, but it was both technologically and financially prohibitive. The article concludes
thusly:

“With the advent of stereo and three-channel recording, nearly three times the equipment, with
more elaboration, seems indicated, and expansion of console area in the horizontal plane offers the
only direction in which to proceed. But a single engineer has arms only so long.”

How times have changed!

Using the Parametric Equalizer

Great care must be exercised when using equalization. The following paragraphs give some general
hints and precautions for using the 528E’s parametric equalizer (or any other equalizer, for that matter).

Beware of Distortion and Noise

When a frequency or group of frequencies are boosted, the overall operating level is boosted as
well. For example, 12 dB of boost (no matter what the frequency) increases the 528E’s output
level 12 dB (at that frequency). This kind of boost reduces headroom by 12 dB in every circuit
from the 528E’s own line driver to the last device in the signal chain (transmitter, tape machine, or
what have you). Unless signal levels are very low to begin with, the 528E’s output gain will have
to be reduced to compensate for increased levels whenever the equalizer is used for boost.

The Clip LED in the Output LED meter monitors levels in the equalizer as well as at the output of
the 528E. If the Clip LED glows, try switching the equalizer to Bypass. If the LED still glows,
reduce the setting of the Output Gain control. If switching the equalizer to Bypass eliminates the
clip indication, then the input level must be reduced via the Mic Gain control or by lowering the
level of the line input.

528E

16

On the other hand, if the levels within the 528E are too low to start with, using the equalizer for
boost may increase noise to unacceptable levels.

If levels are too low, increase the preamp gain (or the output level of the device feeding the line input).

Know What You Are Listening To

Low frequency boost may increase the level of some frequencies that cannot be heard, for one
reason or another. Many high quality microphones are capable of generating substantial output at
very low frequencies (below 50 Hz) which cannot be adequately reproduced by most monitor
speakers or headphones. Be aware that the true effects of low frequency boost may not be audible,
and may actually result in a “muddy” or distorted sound.

Use Wide Peaks, Narrow Dips

In general, the human ear prefers wide bandwidth peaks and narrow bandwidth dips. Boosting a
narrow bandwidth produces a sound usually perceived as “offensive,” while 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’s missing when a narrow bandwidth (.3 octave
or less) is cut, even when it’s cut as much as 30 dB. But, cut a wide bandwidth and the resulting
sound quality is often called “empty.”

Tuning the EQ/Notch Filter

To “tune” the equalizer, use full boost. For both boost and cut, the 528E’s parametric equalizer is
intended to be put to work on specific frequencies. To find a particular frequency “by ear” (the
method used by everyone who doesn’t have a real-time analyzer), turn the cut/boost control all the
way up to +15 dB (be very careful of feedback if you are monitoring on a loudspeaker!). Set the
bandwidth for about .3 octave (max CCW). Tune the frequency control until you distinctly hear the
part of the sound you wish to control. Then, adjust the cut/boost control for the appropriate amount
of change, and readjust the bandwidth control if necessary.

Equalizing for Speech

In broadcast, equalizers are often used to create a sonic personality for the station’s on-air talent. In
production applications, it is practical to write down each person’s settings. In broadcast applica­tions (on-air), most stations try to find a single composite setting that works for all of their on-air
talent. If your station’s on-air talent is comprised of both men and women then finding a single,
compromise setting becomes more difficult. A possibly more workable solution might be to use a
single-D3 microphone (so it has proximity effect) and to vary the working distance to alter the low­frequency response somewhat.

Some general thoughts on speech equalization:

1. Try to use wider bandwidths. Narrower bandwidths (1/2 octave and less) are less audible
(harder to hear) and are generally only useful for remedial work. Broader bandwidths are
less obnoxious, more pleasing sounding, and easier to work with (especially if you’re
boosting a range of frequencies).

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 is equivalent to a boost at the frequencies surrounding the cut.

4. A quick way to figure out what’s going on is to set the level of one band of the equalizer
to full boost (+15 dB), then switch to the frequency control and vary the frequency of that
band of the equalizer while listening to program material fed through the unit. This usually
makes quick work out of finding the region that you want to work on. Now reduce the level
setting to something tasteful.

528E

17

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 the numbers that make
equalizers happy. The following table list some commonly used adjectives and their corresponding
frequency ranges.

Range Description (women) Range Description (men)

100-250 Hz Fullness 75-200 Hz “Balls”, rumble, heaviness
250-400 Hz Bassiness, bigness 200-300 Hz Bassiness, bigness
400-600 Hz Warmth 400-600 Hz Chesty
600-1 kHz Volume 600-1 kHz Volume
2 kHz-4 kHz Clarity 2 kHz-4 kHz Clarity
3 kHz - 5 kHz Nasal, yell, presence 3 kHz-5kHz Nasal, yell, presence
5 kHz-8 kHz Enunciation, intimacy 5 kHz-8 kHz Enunciation, intimacy
10 kHz up Air, mouth noises 10 kHz up Air, mouth noises
To tailor your station’s announce sound, begin with an idea of what general sound you want. Since

you only have three general locations that you can equalize at, you’ll need to begin with the
aspects of your sound that are most important. The choice of microphone is very important, since
every microphone imparts its own equalization to any sound that it hears. If you want a large,
“ballsy” sound, you ought to think about single-D cardioid microphones such as those made by
AKG, Shure, Neumann, Sennheiser, and EV (like the RE38N/D or ND series) or a ribbon micro­phone such as the RCA 77DX. The built-in bass boost caused by close talking a single-D micro­phone (proximity effect) can be tailored or tamed with careful equalization, which also reduces
room rumble at the same time. Last, since the proximity effect increases with decreasing source­microphone distance, a skilled user can substantially change their sound simply by moving in or
out from the microphone.

If clarity is your goal, then a variable-D4 microphone such as the EV RE-20, RE-27 or RE-18 or
an omnidirectional type such as the EV RE50 or AKG414 (with the pattern set to omni) is a good
choice as these types do not emphasize the bass frequencies when you close-talk them. On the
negative side, any room rumble present with the microphone will be boosted along with the voice
if you try to equalize at the lower frequencies.

Next, add or remove low frequencies in the 100-300 Hz range until you get a weight or fullness
that is pleasing. 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
10000+ Hz range to get the sense of brilliance that you want.

The chart on the next page shows the relationships of many different instruments, and a piano
keyboard along with the frequencies involved.

Notes

1

Equivalent input noise (EIN) is a method of modeling the noise performance of a preamp as the signal
level of an equivalent noise source connected to the input of a noiseless preamplifier. The thermal noise
of a 150-ohm resistor is about -133dBV; this represents the theoretical best case.

2

The majority of the material in Section 2.2 is taken from “Equalizing for Spectral Character,”

Langevin Corporation, 1966 Catalog.

3

A single-D microphone is a directional microphone having its rear-entry port(s) spaced at a single
distance from the diaphragm. Single-D microphones are always characterized by proximity effect, a rise
in the bass response at short working distances.

4

528E

A variable-D cardioid microphone has multiple rear entry ports spaced at varying distances from its
diaphragm. Variable-D microphones have little or no proximity effect. Variable-D is a trademark of
Electro-Voice Inc.

18

9

B

PICCOLO

FLUTE

OBOE

WIND

INSTRUMENTS

CLARINET

TRUMPET

FRENCH HORN

TROMBONE

BASS CLARINET

BASSOON

15804.40

9393.20

8372.00

7902.20

7040.00

6272.00

5587.60

5274.00

4698.60

4186.00

3951.10

3520.00

3136.00

2793.80

2637.00

2349.30

2093.00

1975.50

1760.00

1568.00

1396.90

1318.50

1174.70

1046.50

987.77

880.00

783.99

698.46

659.26

587.33

523.25

493.88

440.00

392.00

349.43

329.63

293.66

261.63

246.94

220.00

196.00

174.61

164.81

146.83

130.81

123.47

110.00

98.00

87.31

82.41

73.42

65.41

61.74

55.00

49.00

43.65

41.20

36.71

32.70

30.87

27.50

24.50

21.83

20.60

18.35

16.35

14080.00

12544.00

11175.20

10548.00

TREBLE

BASS

528E

9

A

9

G

9

F

9

E

9

D

9

C

8

VIOLIN

SOPRANO

VIOLA

ALTO

TENOR

CELLO

BARITONE

BASS

BASS TUBA

KETTLE DRUM

BASS VIOL

STRING

INSTRUMENTS

HUMAN

VOICE

B

8

A

8

G

8

F

8

E

8

D

8

C

7

B

7

A

7

G

7

F

7

E

7

D

7

C

6

B

6

A

6

G

6

F

6

E

6

D

6

C

5

B

5

A

5

G

5

F

5

E

5

D

5

C

4

B

4

A

4

G

4

F

4

E

4

D

4

C

3

B

3

A

3

G

3

F

3

E

3

D

3

C

2

B

2

A

2

G

2

F

2

E

2

D

2

C

1

B

1

A

1

G

1

F

1

E

1

D

1

C

0

B

0

A

0

G

0

F

0

E

0

D

0

C

19

Using the 528E Chapter 7

This section is intended for more advanced users. If you are a first-time user, we recommend that
you start out by using the procedure found in “Fast Setup.”

Block Diagram

Figure 7-1 on the next page is the block diagram for the 528E. Please take a moment and take note
of the following:

• The equalizer and de-esser are hard-wire bypassed by their IN/OUT switches.

• The interstage patch points use TRS jacks wired for unbalanced operation.

• The interstage patch points are half-normalled. The send jack does not break the signal flow.

The output level of the 528E can be set to either line level or mic level. The switch for this
function is internal to the unit. Refer to Appendix A.

Installation

The 528E may be installed freestanding or rack mounted. Rubber feet are included for freestanding
use. No special ventilation requirements are necessary. Table 7-1 lists the 528E’s requirements for
installation.

Installation Requirements

Mechanical One rack space (1.75 inches) required, 12.5 inches depth (including connector

allowance). Rear chassis support recommended for road applications.

Electrical 105-125V ac, 12.5 Watts maximum. 210-250V ac, 50 Hz, 12.5W maximum

(export).

Connectors XLR-3 female for inputs, XLR-3 male and TRS 1/4-inch female for outputs, Pin 2

of the XLR connectors is “Hot.”
The sidechain access jack output uses a TRS jack wired as an insert jack (tip=return, ring=send).
The interstage patch points use TRS jacks with the ring and sleeve connections connected to

circuit ground. The jacks are half-normalled (only input breaks normal).

Level Setting

For optimum noise performance, correct level settings are a must, especially for microphone
sources. You should operate the 528E’s mic preamp at the highest gain possible without overload.
Extremely hot signals may require using the -15 dB pad switch.

The 528E expects line level signals to fall in the +4 dBu region. Lower signal levels are okay, but
the noise performance may suffer as there is no gain trim control for the line input.

The CLIP LED in the mic input section of the 528E actually monitors the output of the MIC-LINE
switch. If the LED glows, and you are using the MIC input, then reduce the setting of the MIC GAIN
control until the LED no longer glows. If you are using the LINE input, reduce the level of the
device driving the 528E.

The CLIP LED in the OUTPUT LED meter monitors levels in the equalizer as well as at the output of
the 528E. If the CLIP LED glows, try switching the equalizer to BYPASS. If the LED still glows,
reduce the setting of the OUTPUT GAIN control. If switching the equalizer to BYPASS eliminates the
clip indication, then the input level must be reduced via the MIC GAIN control or by lowering the
level of the line input.

528E

20

DE-ESS

IN/OUT

EQ

INPUT

OUTPUT

EXP/COMP

GAIN

EXPANDER/COMPRESSOR

EXTERNAL SIDECHAIN

(RING=SEND. TIP=RETURN)

OUTPUT STAGE

INPUT

EQ

OUTPUT

BALANCED

OUTPUT

OUTPUT

UNBALANCED

REV-F

THRESHOLD

FREQUENCY

CLIP

MIC GAIN

+48V/BYPASS IN/OUT

DE-ESS

PREAMP

PAD

-15dB

POWER

PHANTOM

EQ

IN/OUT

IN/OUT

EXP/COMP

COMPRESSOR

RATIO

COMP

EQ

EQ

EQ

HIGH

MID

LOW

THRES

COMP

EXPANDER

EXP

THRES

MIC

LINE

SUPPLY

DOWNWARD

CUT/BOOST CUT/BOOST CUT/BOOST

BANDWIDTH BANDWIDTH BANDWIDTH

FREQUENCY FREQUENCY FREQUENCY

INTERNAL

OUTPUT LEVEL

SELECT SWITCH

EQ CLIP DETECTION

OUTPUT LEVEL DISPLAY

VOICE

IN/OUT

SYMMETRY

OPTIONAL

POWER SWITCH

CIRCUIT

SELECTION

OUTPUT LEVEL

MUTE

THUMP

OUTPUT

CIRCUIT

OUTPUT STAGE

WITH SYMMETRY

CORRECTION CIRCUIT

SUPPLY

POWER

SS
E

R
P

S
S
E
R
P

Figure 7-1. 528E Block Diagram

528E

21

Operational Details

FRONTPANEL

MIC INPUT

BYPASS

+48V

POWER

PHANTOM

LINE INPUT

PRE-AMP

OUTPUT

STAGE

INPUTOUTPUT

SIDECHAIN

RING=SEND

TIP=RETURN

INPUT

DE-ESSEQUALIZER

INPUTOUTPUT

BALANCED OUTPUT

OUTPUT

UNBALANCED

INPUT

OUTPUT STAGE

OUTPUT

EXPANDER/COMPRESSOR

`MIC' POSITION

SWITCH IN

INPUT SELECT

RPESSSESPR

FRONTPANEL

SWITCH IN `LINE'

(OUT) POSITION

INPUT SELECT

RETURN INPUT

TO CHANNEL PATCH

PATCH SEND OUTPUT

FROM CHANNEL

MIC INPUT

BYPASS

+48V

POWER

PHANTOM

LINE INPUT

PRE-AMP

OUTPUT

STAGE

INPUTOUTPUT

SIDECHAIN

RING=SEND

TIP=RETURN

INPUT

DE-ESSEQUALIZER

INPUTOUTPUT

BALANCED OUTPUT

OUTPUT

UNBALANCED

INPUT

OUTPUT STAGE

OUTPUT

EXPANDER/COMPRESSOR

RPESSSESPR

This section describes the details of operating the 528E. Usage information can be found later in
this chapter.

The 528E accepts monaural analog input signals at mic or line level, processes them, and delivers
them back to you as balanced line, unbalanced line or balanced mic level signals.

Stand-alone Operation

A vast majority of users use the 528E as a stand-alone device. Here the 528E replaces their usual
microphone preamp and either feeds their tape machine or workstation directly, in essence
becoming a one-input, one-output console. Figure 7-2 illustrates the connections needed.

Figure 7-2. Hookup for stand-alone operation

Figure 7-3. Using the 528E as a channel insert device

528E

22

For best results, the 528E should replace the mic preamp in your console or recording chain. If you
have to plug the 528E into a microphone input (-40 dBu nominal level), then you’ll need to pad
(attenuate) the output of the 528E down to microphone level. An internal jumper connection
reduces the 528E’s output to this level. Although a far preferable connection would be to bypass
your console’s mic preamp, this will work. When configured for mic-level output, the 528E’s
circuitry doesn’t care if phantom powering is or isn’t present at the console’s mic input. Appendix
A contains instructions for altering the output level of the 528E.

Note: Padding (attenuating) the output of the 528E back to microphone level is a workable
solution towards interfacing the 528E into a console or system having only microphone level
inputs. However workable, the ultimate performance of the 528E will be limited by the perfor­mance of your system’s existing microphone preamps. If you can find a way to bypass the existing
microphone preamps in your system, do so. It’ll be worth the trouble.

Using the 528E as a Channel Insert Device

The 528E can also be used as a channel-insert device with your console. Use the 528E’s line input
and line output as shown in Figure 7-3.

Using the 528E in an Effects Loop

Signal processors used in a console’s effects (send-receive) loop should not be insert or series
processors. A series processor means that you have to break the signal path to insert the processor.
Since using the effects loop does not break the signal path, we don’t recommend that you connect
the 528E here. Use the channel-insert jacks as described under the previous heading or insert the
528E between your console and your tape machine.

1

Using the Patch Points

Located on the rear panel are several TRS jacks. These jacks are the connections between the
various processors that make up the 528E. The jacks are half-normalled, which means that without
any plugs inserted, the signal flows through them via internal switching contacts. The term “half
normal” means that only the input or return jack has switching contacts; inserting a plug into the
output or send jack does not break the signal path. This allows you to access the signal at various
points in the 528E’s signal path for use with external processors.

The patch point jacks can be used to insert additional processing into the signal path or perhaps to
rearrange the sequence in which the individual processors receive the input signal. Still another
possibility would be to use the parametric equalizer in the sidechain of the compressor/downward
expander (for additional information on using the sidechain, see the end of this chapter).

Inserting Additional Processing

Figure 7-4 shows an external processor inserted between the 528E’s equalizer and its output stage.
To insert additional (external) processing into the 528E’s signal path:

1. Decide where in the signal path you wish to insert the external processor.

2. Patch the appropriate output jack
on the 528E to the input jack of the
external processor. Use either a
TRS or TS patchcord.

3. Patch the output jack of the external
processor to the corresponding
input jack on the 528E. Use either a
TRS or TS patchcord.

OUTPUT STAGE

UNBALANCED

OUTPUT

INPUT

EQUALIZER

OUTPUT

EXPANDER/COMPRESSOR

SIDECHAIN

OUTPUTINPUT

TIP=RETURN

RING=SEND

INPUTOUTPUT

EXTERNAL AUDIO PROCESSOR

OUTPUT INPUTINPUT

PRE-AMPDE-ESS

STAGE

OUTPUT

LIN

1

An insert or series processor is one that is inserted in series with the signal to be modified. Generally speaking,
series processors have a wet-dry mix control, however compressors, expanders, gates, equalizers, as well as the
528E, are all series processors that don’t.

Figure 7-4. Inserting additional processing

23

528E

Changing the Sequence of Processing

You may wish to change the sequence of processing within the 528E to allow the signal processors
to work on the input signal in a particular way (your way). A good example of this is the compres­sor: should the equalizer precede or
follow the compressor. Most studio
engineers would have the equalizer
follow the compressor, like it nor­mally does in the 528E. In broadcast,

OUTPUT STAGE

UNBALANCED

OUTPUT

INPUT

EQUALIZER

OUTPUT

EXPANDER/COMPRESSOR

SIDECHAIN

OUTPUTINPUT

TIP=RETURN
RING=SEND

OUTPUT INPUTINPUT

PRE-AMPDE-ESS

STAGE

OUTPUT

many engineers prefer the opposite;
the compressor receives the output of
the equalizer. Figure 7-5 illustrates
this patch.

Figure 7-5. Changing the sequence of processing

Using the Equalizer in the Sidechain

For some applications, you may want
the 528E’s equalizer in its sidechain
rather than in the signal path. Doing
so makes both the compression and
downward expansion frequency
conscious. Figure 7-6 illustrates this
patch. You can find out more about
using the sidechain in Chapter 8.

OUTPUT STAGE

UNBALANCED

OUTPUT

INPUT

EQUALIZER

OUTPUT

EXPANDER/COMPRESSOR

SIDECHAIN

OUTPUTINPUT

TIP=RETURN
RING=SEND

NOTE: SPECIAL
WIRING NEEDED

INPUT
TO RING

OUTPUT
TO TIP

OUTPUT INPUTINPUT

PRE-AMPDE-ESS

STAGE

OUTPUT

LIN

LIN

Figure 7-6. Using the equalizer in the dynamics
processor’s sidechain

528E

24

Tips and Techniques for Using the 528E

Following are some tips and techniques for using the 528E. You should consider any settings given
as starting points for developing your own settings. More general discussions of these topics may
also be found in Chapter 6 of this manual.

METERING

The 528E has several LED bargraphs that serve as gain reduction and output meters. The gain­reduction meters indicate the change, from unity gain, for their respective function and the LEDs
read (and move) from right to left. When operating as a level meter, the LEDs read (and move)
from left to right. Each meter has its own scale markings, as shown on the front panel.

GAIN SETTING

There are two places to adjust the gain of the 528E: at the mic input, before any processing, and at
the output. An understanding of this topic is essential to getting the most from your 528E. A more
basic discussion can be found under the heading, “Gain Setting,” in Chapter 7.

First, the mic input gains. You make best use of the 528Es signal-to-noise ratio by ensuring that
your mic-level input signals are adjusted to fit within the headroom of the mic preamp. Doing so
ensures optimum dynamic range through the mic preamp and succeeding processors. With the De­esser, Expander/Compressor, and EQ sections temporarily set to BYPASS and the OUTPUT GAIN
control set to 0 dB (12:00 o’clock), set the MIC GAIN control so that the OUTPUT LEVEL display
indicates levels in the -10 to 0 VU range. The CLIP LED should never illuminate on signal peaks.
Remember to restore the settings of the various bypass switches.

Finally, the OUTPUT GAIN. After adjusting all of the other processors, set this control so that the 0
VU LED on the OUTPUT LEVEL meter illuminates. The red CLIP LED should never illuminate.

The output CLIP LED also monitors the EQ section. If the CLIP LED illuminates, reduce the OUTPUT
GAIN control setting slightly. You may need to increase the gain of some device following the 528E
to achieve the same overall level.

EQUALIZATION

Bandwidth specs, in octaves, for some popular equalizers.

Name BW (min) BW (max)

API 550 1.6 n/a
Focusrite 0.6 1.8
Neve V3 0.2 3.0
SSL G 1.4 2.8
SSL E 0.5 2.5

The 528Es parametric equalizer has three overlapping bands. Each band can operate as a peaking
or dipping equalizer. The boost and cut range for each band is ±15 dB. The bandwidth may be
varied from 0.3 to 4-octaves wide.

Since the bands overlap, it is possible to apply equalization at the same frequency in two places.
Doing so could conceivably increase the signal level by 30 dB at one frequency. You may need to
reduce the INPUT or OUTPUT GAIN to avoid distortion. Likewise, large amounts of boost in any one
band may require reducing the setting of the OUTPUT GAIN control to prevent overload. Let the
OUTPUT CLIP LED be your guide.

Electronic considerations aside, one of the contributing factors to an equalizer’s sound is its
bandwidth. The table above lists the bandwidths (octaves) for several (possibly) familiar equaliz­ers, as found on their respective mixing consoles. While we make no promise that the 528E will
sound the same, these settings may be a good starting point if one of these equalizers is within your
frame of reference.

528E

25

A parametric equalizer offers perhaps the greatest flexibility of any type of equalizer, however it
can be more difficult to arrive at a setting than with other equalizers. A good strategy for setting
any equalizer is to set the level control for maximum boost, then vary the Frequency and Band­width until you locate the portion of the spectrum that you wish to modify. Then refine the setting
of the Level control for that band. Next refine the setting of the Bandwidth control. You may have
to go back and forth between Level and Bandwidth to find the magic setting. Toggling the EQ
Bypass switch between in and out can help too.

As a rule, it is much easier to hear changes in amplitude (level) than it is to hear bandwidth
changes. It is also easier to hear the abundance of something rather than the absence of the same
thing. Even if you intend to apply cut (negative level) to a particular frequency, it is still easier to
find that frequency by boosting first, tuning second, and resetting the boost/cut last according to
taste or need. Finally, you may find that more natural sounds result when you use wider band­widths for boosting, narrower bandwidths for cutting. Regardless, there are no hard and fast rules
and in the end, whatever works for you is best.

It’s generally easier to apply boost to a sound for shaping (and that’s how many engineers start).
Many times, however, you may want to experiment with removing an offending sound (as opposed
to drowning it out with something else). In a complex mix, this may work better because it may
require less overall EQ to remove the offending sound; the end result will sound more natural.

DE-ESSER

The de-esser uses a variable-frequency crossover whose outputs are mixed. The high-frequency
path through the mixer is controlled by a VCA whose gain is a function of the sibilance content of
the input signal. In sibilant speech, the dominant frequency component is the sibilance itself.
Reducing the level of high-frequencies during periods of sibilance reduces the level of the sibilant.

Set the de-esser by adjusting the THRESHOLD level until the de-esser’s gain reduction display
indicates around -12 dB. Now “tune” the FREQUENCY control until the sibilance is no longer
objectionable. Finally, modify the THRESHOLD control setting until you have the desired degree of
de-esser action.

COMPRESSION

The compressor generally controls peak levels and helps to maintain a high overall average signal
level. Used in this manner, the compressor’s action is generally inaudible. Compressors can also
be used creatively, to make a source sound louder than it really is, or to create a special effect.

For most level control applications, moderate settings yield the best results. We recommend a
starting point of: COMP THRESHOLD control setting sufficient to cause about 6 to 8 dB of gain
reduction on peaks using a COMP RATIO setting of 4:1.

For a highly compressed sound (you know, the used car salesman during the 3AM movie), use a
10:1 ratio setting and 10 dB or more of gain reduction.

DOWNWARD EXPANDER

The downward expander reduces its gain for any signal level below its threshold setting. Typically,
downward expanders are used to remove noise or unwanted signal from an audio signal by simply
lowering the gain when the overall level falls below threshold.

Think about using the expander when you are faced with a noisy signal (not necessarily hiss) or
when heavily compressing a voice and you want to remove some of the less desirable artifacts
(false teeth rattling, lip smacking, tongue noise, etc.) You can also use the expander to help remove
microphone leakage from a signal.

Start by setting the threshold so that the expander causes gain reduction (left LED meter) as the
signal falls in level. Increasing threshold levels (less negative numbers) cause further reductions in
the overall gain as the signal level falls.

528E

26

USING THE SIDECHAIN

The sidechain is a patch point in the control circuit of a dynamic range processor, which provides
access to the part of the circuitry that tells the VCA what to do. The 528E’s sidechain routes
through a rear panel TRS jack that allows the control signal to be processed outside the unit (see
Figure 7-6 for specific hookup information).

Refer to the block diagram at the beginning of this chapter. Notice the sidechain connections that
come from the compressor/downward expander section. These connections allow access to the
audio signal at the input to the control circuit that drives the dynamics processor. This control
signal is derived from, but kept totally separate from, the audio signal path, which means that the
control signal can be processed outside the 528E without actually processing the signal that’s going
through the VCA (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 528E’s compressor/downward 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 VCA 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 VCA prevents those frequencies from being used to create gain changes.
Applications utilizing the sidechain may be found in the next chapter of this manual.

THE VOICE SYMMETRY SWITCH

Human speech, especially male human speech, contains a great deal of asymmetry. In broadcast
(especially AM broadcast), this wastes transmitter power because the asymmetrical waveforms do
not utilize the full power of the modulator. The bottom line is that you risk negative
overmodulation if you don’t correct speech asymmetry before the modulator. The VOICE SYMMETRY
switch corrects asymmetric speech waveforms before they get to your board; an added bonus is
that you can apply the correction only to the announce mics without affecting the music.

In recording applications, this switch may help give slightly higher overall levels by improving the
symmetry of speech signals which may allow lightening up on the compression. Non-speech
signals may be adversely affected by the VOICE SYMMETRY switch. Let your ears be your guide.

528E

27

Applications Chapter 8

The 528E Voice Processor was designed to make the same kind of specialized processing that’s
applied to voice-overs and vocal tracks in recording studios available for use in broadcasting,
paging, public address and sound reinforcement. In a recording studio, four or five separate pieces
of equipment are usually patched together to obtain the kind of processing provided by the 528E.

For the highest level of versatility, we recommend making the output/input patching and sidechain
connections available by wiring the unit to a patch bay. Be sure that the interstage patch points are
normalled together (we recommend half-normalling) and that the sidechain connection terminates
in two half-normalled jacks. This allows access to the individual sections of the 528E, provides for
easy use of the sidechain, and allows the processing order to be changed at will (to place the
parametric in the sidechain, for instance).

The following discussions illustrate some of the more useful applications for the 528E. Because of
its versatility, combinations of the applications described here will normally be used.

Broadcast Applications

With the 528E, a variety of common problems can be corrected, and overall sound quality can be
greatly improved. In addition to its “normal” use with announce mics, there are several more
specialized uses for the Voice Processor. This section provides general operating guidelines for the
various parts of the 528E, and also describes typical applications used in the production room for
special effects, in the news room for cleaning up actualities and phone feeds, and in television for
PA feed to a studio audience.

The applications that follow are merely operational guidelines for the Voice Processor. The
particular kind of processing applied in any given situation must be determined by the problems
encountered, and by the dictates of the format. What’s necessary or appropriate in one case, may
not be at all proper in another.

Announce Mics - Compressing, Limiting, Expanding

The 528E’s dynamic range processor is used to control both over-modulation and noise. Noise, in
this case, may be electrically induced (hum, buzz, etc.), or acoustically transferred (paper rattling,
cart solenoids, air conditioning, etc.), since the downward expander attenuates all below threshold
signals without regard to origin. Careful adjustment of the two threshold controls allows the
operator to put the 528E to work on any portion of the dynamic range. The expand threshold
control governs the 528E’s activity in the lower part of the dynamic range, while the comp
threshold governs activity in the upper part of the range.

For smooth overall dynamic range processing that will tend to “homogenize” the sound and
remove only very low level noises, use a gentle compression ratio with a relatively high comp
threshold, and a relatively low expand threshold.

The soft-knee transition characteristic of the interactive processor allows the use of much higher
compressor/limiter ratios with much lower thresholds. The expander’s rapid rise below its thresh­old, combined with the compressor’s smooth transition through its threshold, makes processing go
unnoticed. Use this application to “tighten up” voice-overs. The expander eliminates noise and
adds “punch.”

The expander may be used without the compressor to remove background noise. Be sure the
expand threshold is set low enough to allow even the lowest level speech sounds to pass, and the
compression ratio is set to 1 (so the compressor/limiter is essentially out of circuit).

Likewise, the compressor/limiter may be used without the expander to control only the upper end
of the dynamic range. For general purpose overall gain control, use compression. Set the ratio
between 2:1 and 3:1, with a comp threshold setting that results in 6dB to 10dB attenuation.

Limiting is used for very definite control of the maximum level. As the name implies, limiting sets
the upper limit, but is not intended for general purpose oveall gain control. For limiting, set the

528E

ratio at 10:1, with the comp threshold control set to provide no more than 3dB to 6dB attenuation.

28

Bear in mind that limiting is an extreme dynamic control action intended to prevent overload
farther down the line. Limiting may be more pleasing to the ear than clipping distortion, but it
doesn’t sound good enough to be used for more than 6dB attenuation.

Using the De-esser

De-essers are used to reduce the level of certain high frequency vocal sounds like sibilance,
overemphasized fricatives, and lip smacking. The 528E’s de-esser provides control over much
lower frequencies than would normally be considered “essing.” The additional control range
greatly enhances the versatility of the de-esser.

Cleaning Up News Feeds

Use the de-esser to reduce unnatural high frequencies, the compressor/limiter to prevent overload,
the expander to eliminate noise, and the parametric to make the feed sound better and/or get rid of
interference (hiss, noise, extraneous sound, etc.).

Actualities carts1 that are prepared with the 528E produce an end product with better intelligibility
and improved signal to noise ratio. The object of the processing is to keep dynamic range within
the real limits of the recording equipment, to eliminate extraneous noise, and to get better sound.

Increasing Gain Before Feedback

To optimize a PA system’s response for minimum feedback, tune out the feedback using the
parametric equalizer. To find and eliminate resonances that can become feedback problems, turn
the system on, with the microphone(s) and speaker(s) in place as they will normally be used, then
follow the sequence below. Gain before feedback should increase about 6dB (perhaps as much as
15dB) with this technique.

1. Note the settings of each of the compressor controls.

2. Temporarily set the compressor ratio to 10:1. Increase system gain very carefully until a
feedback frequency becomes slightly audible.

3. With the bandwidth set at about .3 octave, and the cut/boost control set for about -15dB, tune
the frequency control of one section until the feedback is no longer audible.

4. Increase system gain until feedback becomes slightly audible again.
A. If it’s the same frequency that was heard first, readjust the same frequency and bandwidth

controls until it again subsides.

B. If it’s a new frequency, repeat Step 2 using another of the EQ sections.

5. Increase gain again to find the third most prominent feedback frequency. Repeat Step 2 using
yet another of the EQ sections.

6. Reduce system gain to normal operating levels.

Parametric EQ in the Sidechain

The parametric equalizer can be placed in the sidechain of the dynamic range processor to make
compression, limiting, or expanding action frequency sensitive. The equalizer is patched into the
sidechain, so the audio signal that will ultimately become the VCA’s control voltage can be
equalized before being fed to the detector circuitry (see Chapter 6 for additional information and
Chapter 7 for hookup details).

To make the 528E’s compressor/limiter more sensitive to high frequencies, boost the high frequen­cies on the equalizer. This increases the sensitivity of the compressor’s control circuits to those
particular frequencies, so the compressor/limiter responds more to those frequencies than any
others (in effect, the threshold setting is lowered by the extent that the high frequencies have been
boosted). Juggling the relationship between the amount of boost and the threshold setting can have
the effect of only compressing when the signal contains significant energy in the region boosted by

528E

29

the equalizer. Likewise, cutting or attenuating certain frequencies desensitizes the compressor to
those frequencies.

Keep in mind that the COMP THRESHOLD becomes a function of the amount of overall gain through
the equalizer, including the boost. This technique can be used with any frequency that can be
controlled by the equalizer.

Using Sidechain EQ to Enhance Expander Action

Since the expander can only discriminate between different levels (not different sounds), it can be
fooled by signals whose levels are nearly the same, even if the frequency content of those signals is
fundamentally different. When the 528E’s expander is used to shut out unwanted sounds, any
signal that exceeds threshold will trigger the expander. When unwanted signals trigger the system,
it’s often possible to eliminate the false triggering by equalizing the control signal.

For example, if low frequency signals transmitted through a desk or podium are triggering the
528E’s expander unnecessarily:

With an equalizer in the sidechain, remove the low frequencies from the control signal, and/or
boost the higher voice range frequencies.

When the offending frequencies are removed, and the relative level of the desired frequencies is
increased, the expander can tell the difference between the wanted and unwanted signals. Use this
technique in any situation where levels are nearly the same, but the fundamental frequencies
involved are different.

Note The ability of the expander to discriminate between wanted and unwanted signals is

determined in part by mic technique. Be particularly careful of high frequency sounds
entering the side or rear pattern of a cardioid mic. Most cardioids exhibit a sharply rising
off-axis response characteristic at higher frequencies. Check the off-axis curve (the lower
one) in the manufacturer’s literature. If there’s only a 3dB to 6dB difference between the
on-axis (front) response and the off-axis (side or rear) response in the 5kHz to 10kHz
region, high frequency sounds will be picked up by the side or back of your mic.

Use the mic’s directional pattern to keep other sources as far off-axis as possible - do
everything you can to extract all the source-to-source discrimination possible through
good mic technique. The sounds picked up by individual mics must be primarily the
sound of the desired signal, or the expander won’t be able to tell the difference.

Using Reverb or Effects

Effects usually require another mixer input for effects return. However, the 528E’s patching
connections can be used to feed a signal to the effects unit, and the output stage input can be used
to return the effects signal to the 528E’s output. The only requirement is that the effects device
have a mix control to set the direct/effects signal mix. If you need a hookup diagram, you’ll find
one in Figure 7-4.

Vocal Processing - Recording and Reinforcement

The 528E handles a wide variety of program material with ease. When recording vocals, the
undesirable side effects that usually result from high ratio comp/limiting, like headphone leakage
and room noise, can be reduced with the 528E’s interactive expander processing. During
mixdown the 528E not only provides compression, but also eliminates the noise that often accom­panies vocal tracks that are processed with high frequency EQ, compression, or both.

In sound reinforcement situations, if the threshold has been set correctly, the expander will
attenuate whenever a mic is not in use, eliminating extraneous pickup of stage sounds, and reduc­ing feedback from monitor speakers. The operating principle is the same for both the recording
and reinforcement situations.

528E

30

Adding Dynamics, or “Punch”

By setting the expand threshold above the level of the program material, the 528E can be made to
behave like a linear expander (see Chapter 6). With this technique, the 528E can simultaneously
create a more dynamic feel, add compression, and reduce noise. Use this kind of processing for
special effects, and to increase the dynamic feel of percussive instruments like electric bass, snare
drum, rhythm guitar, etc.

Set the expander threshold above the signal level. The compressor/limiter is used to control peaks
(and with certain instruments like electric bass, to put in a little more “bottom” by creating extra
sustain). Set the comp threshold so the maximum compression is about 6dB with ratios below 2:1,
or 3dB with ratios above 2:1.

Since this kind of processing reduces overall output level, use the output gain control to bring
levels back up to normal.

High Level Stage Monitors - Dynamic Processing

Public address and sound reinforcement situations that require compression/limiting are often
plagued by feedback problems. Usually the “make up gain” used with compression causes an
overall increase in level which in turn, can cause feedback in the absence of signal, when the
compressor releases and brings the gain back up to normal.

The 528E’s interactive dynamics processor allows the use of large amounts of comp/limiting
without serious side effects. When compression is applied to “normal” signal levels, the compres­sor returns to unity gain when the signal goes away. This action increases overall system gain. The
528E’s expander, on the other hand, decreases gain whenever signals fall below threshold. Careful
setting of the two threshold controls tells the 528E how and when to adjust the gain.

Stage monitors can be made much “tighter” with compression, but feedback problems often make
even gentle, low ratio compression impossible. The 528E’s interactive processor performs exceed­ingly well in this situation, because the expander decreases gain to compensate for the gain
increase that results from compression.

Careful adjustment of the expander threshold control will prevent feedback in the absence of
signal, even with substantial compression. Note that in most cases the expander threshold must be
set higher than the compressor threshold.

1

An actualities cart is a recording (on a Fidelipac cart) of an actual broadcast. An aircheck by any other

name. Actualities carts are typically used to give someone else a warm fuzzy feeling.

528E

31

Chapter 9Technical Tutorial

This section discusses a multitude of things, all related to getting signals in and out of the 528E.

Matching Levels vs Matching Impedances

In any audio equipment application, the question of “matching” inevitably comes up. Without
digging a hole any deeper than absolutely necessary, we offer the following discussion to (hope­fully) clarify your understanding of the subject.

Over the years, we have all had impedance matching pounded into our heads. This is important
only for ancient audio systems, power amplifiers, and RF. Technically speaking, the reason is
power transfer, which reaches a maximum when source and load are matched. Modern audio
systems are voltage transmission systems and source and load matching is not only unnecessary,
but undesirable as well.

• Ancient audio systems operate at 600 ohms (or some other impedance value), and must be
matched, both at their inputs and at their outputs. Generally speaking, if you are dealing with
equipment that uses vacuum tubes, or was designed prior to 1970, you should be concerned
about matching. These units were designed when audio systems were based on maximum
power transfer, hence the need for input/output matching.

• Power amplifiers are fussy because an abnormally low load impedance generally means a visit
to the amp hospital. Thus, it’s important to know what the total impedance of the pile of
speakers connected to the amplifier really is.

• RF systems are matched because we really are concerned with maximum power transfer and
with matching the impedance of the transmission line (keeps nasty things from happening).
Video signals (composite, baseband, or otherwise) should be treated like RF.

Some folks seem to believe that balanced/unbalanced lines and impedances are related; or even
worse that they are associated with a particular type of connector. Not so. Unbalanced signals are
not necessarily high-impedance and balanced signals/lines are not necessarily low-impedance.
Similarly, although 1/4-inch jacks are typically used for things like guitars (which are high­impedance and unbalanced), this does not predispose them to only this usage. After all, 1/4 inch
jacks are sometimes used for loudspeakers, which are anything but high-impedance. Therefore, the
presence of 3-pin XLR connectors should not be construed to mean that the input or output is low­impedance (or high-impedance). The same applies to 1/4-inch jacks.

So, what is really important? Signal level, and (to a much lesser degree), the impedance relation
between an output (signal source) and the input that it connects to (signal receiver).

Signal level is very important. Mismatch causes either loss of headroom or loss of signal-to-noise
ratio. Thus, microphone inputs should only see signals originating from a microphone, a direct
(DI) box, or an output designated microphone-level output. Electrically, this is in the range of
approximately -70 to -20 dBm. Line inputs should only see signals in the -10 to +24 dBm/dBu
range. Guitars, high-impedance microphones, and many electronic keyboards do not qualify as
line-level sources.

The impedance relation between outputs and inputs needs to be considered, but only in the
following way:

Always make sure that a device’s input impedance is higher than the output source impedance of
the device that drives it.

Some manufacturers state a relatively high-impedance figure as the output impedance of their
equipment. What they really mean is that this is the minimum load impedance that they would like
their gear to see. In most cases, seeing a output impedance figure of 10,000 (10K) ohms or higher
from modern equipment that requires power (batteries or AC) is an instance of this type of rating.
If so, then the input impedance of the succeeding input must be equal to or greater than the output
impedance of the driving device.

528E

Symetrix equipment inputs are designed to bridge (be greater than 10 times the actual source
impedance) the output of whatever device drives the input. Symetrix equipment outputs are

32

designed to drive 600-ohm or higher loads (600-ohm loads are an archaic practice that won’t go
away). You don’t need to terminate the output with a 600-ohm resistor if you aren’t driving a 600­ohm load. If you don’t understand the concept of termination, you probably don’t need to anyway.

The two facts that you need to derive from this discussion are:

1. Match signal levels for best headroom and signal-to-noise ratio.

2. For audio, impedance matching is only needed for antique equipment and power amplifier
outputs. In all other cases, ensure that your inputs bridge (are in the range of 2 to 200 times the
output source impedance) your outputs.

Signal Levels

The 528E is designed around studio/professional line levels: +4 dBu or 1.23 volts. The unit is quiet
enough to operate at lower signal levels such as those found in semi-pro or musical-instrument
(MI) equipment (-10 dBu or 300 millivolts).

The microphone input is designed to accept low-impedance microphones. Switchable 48V phan­tom powering is provided for suitable condenser microphones. The microphone input accepts
signal levels from -60 to -5 dBV (+10 dBV with the -15 dB pad).

The line input is designed to accept nominal line level: +4 dBu.
The output line driver delivers +4 dBm into 600-ohm or higher balanced loads. An internal switch

converts the line level output to microphone level, or -36 dBu. An unbalanced output is also available
via a 1/4" TRS phone jack. This jack is always line-level and is unaffected by the internal switch.

I/O Impedances

The 528E is designed to interface into almost any recording studio or sound reinforcement applica­tion. This includes:

• 600 ohm systems where input and output impedances are matched.

• Unbalanced semi-professional equipment applications.

• Modern bridging systems where inputs bridge and outputs are low source impedances

(voltage transmission systems).

The 528E’s microphone input is intended to bridge a 150-ohm balanced source. The actual input
impedance is approximately 8-kilohms. 48V phantom powering for condenser microphones is
present if the PHANTOM POWER switch has been depressed. Refer to the discussion of phantom
powering on the next page for additional information.

The 528E’s line input impedance is 10-kilohms balanced, and 10-kilohms unbalanced. The inputs
may be driven from any source (balanced or unbalanced) capable of delivering at least -10 dBu
into the aforementioned impedances.

The 528E’s output impedance is 200 ohms balanced, 100 ohms unbalanced. The output line driver
delivers +18 dBm into a 600-ohm balanced load or +18 dBm into 600-ohm unbalanced loads.

Polarity Convention

The 528E uses the international standard polarity convention of pin 2 hot. Therefore:

XLR Tip-Ring-Sleeve Signal

1 Sleeve Ground
2 Tip High
3 Ring Low

If your system uses balanced inputs and outputs, and uses the 528E this way, then the polarity
convention is unimportant. If your system is both balanced and unbalanced, then you must pay
attention to this, especially when going in and coming out through different connector types (like
input on an XLR, output on a phone jack).

528E

33

Input and Output Connections

Figure 9-1 illustrates how to connect the 528E to balanced and unbalanced sources and loads.
To operate the 528E from line level unbalanced sources, run a 2-conductor shielded cable (that’s

two conductors plus the shield) from the source to the 528E’s line input. At the source, connect the
low/minus side to the shield, these connect to the source’s ground; connect the high/plus side to the
source’s signal connection. At the 528E, the high/plus wire connects to pin 2, the low/minus wire
connects to pin 3, and the shield (always) connects to pin 1. This is the preferred method as it
makes best use of the 528E’s balanced input (even though the source is unbalanced). The other
alternative shown in Figure 3-1 converts the 528E’s balanced input into an unbalanced input at the
input connector. This works, but is more susceptible to hum and buzz than the preferred method.
There is no level difference between either method.

The 528E has two output connectors: XLR-male and TRS female. The XLR connector may be
configured for either microphone-level or line-level output. The TRS connector is always line
level. Refer to Appendix A for conversion instructions.

You can drive unbalanced loads with the 528E’s outputs by using the XLR connector with pin 3
left open. In an emergency (the show must go on), you can ground pin 3, but if you have the
choice...leave it open. If you must ground pin 3, it must be grounded at the 528E, rather than at the
other end of the cable. The price, regardless of whether or not pin 3 is grounded is 6dB less output
level. This can be easily made up via the output gain controls. If your system is wired with pin 3
hot, pin 2 must float if you are driving an unbalanced load.

The 1/4-inch unbalanced output uses a TRS female jack with the ring contact wired to circuit
ground. This jack is unaffected by the internal output level switch. Unlike the XLR connector,
using this jack corrects the gain so that it is unity. The interstage patching jacks are half-normalled
(only the input jack breaks normal) TRS jacks wired for unbalanced operation. This means that the
tip is the signal connection, ring and sleeve are ground. This method of connection allows either
TRS or TS plugs to be used, with either balanced or unbalanced inputs or output on the remote
equipment. Aside from that, the TRS jack grabs the plug better. Ensure that your plug is fully
inserted into the jack.

The sidechain access jack for the dynamics processor uses a TRS jack wired as an insert jack. This
means that the ring connection is the send to and the tip connection is the return from the remote
processor. Figure 9-2 shows the wiring for the plug as well as the connections to/from the external
processor.

Phantom Powering Condenser Microphones

Most modern condenser microphones have provisions for being remotely powered via the micro­phone cable. The dominant system in use today is the phantom power system which is compatible
with both condenser and non-condenser microphones (dynamics, ribbons, etc.). If your
microphone’s data sheet says that it is phantom powered, the 528E can power it1.

Another remote powering system exists called A-B powering, modulation lead powering, or T
system. A-B powering is incompatible with phantom powering as well as other non-powered
microphones.

The technical requirements for operation and/or compatibility are:

• The microphone must have a balanced, low-impedance output.

• The balanced output must be floating with respect to ground. If there is a center tap, it must

also float with respect to ground. (In the past, it was common to ground the center tap of the
microphone’s output transformer. This was especially true of ribbon microphones.)

1

The DIN specification (DIN 45 596) covering phantom powering specifies the phantom powering voltage

528E

as an open-circuit measurement. If you attempt to measure the phantom voltage, make sure that you do
so with the microphone disconnected.

34

FROM BALANCED OUT

FEMALE XLR

PIN 1 = GROUND

PIN 2 = HIGH

PIN 3 = LOW

TO BALANCED IN

2
3

1

2
3

1

MALE 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

TIP = HIGH

SLEEVE = GROUND +

FROM NON-TRANSFORMER (ELECTRONIC)

PIN 1 = GROUND + LOW

PIN 3 = NOT USED

LOW

FROM BALANCED OUT

TERMINAL STRIP

(+) = HIGH

(-) = LOW

= GROUND

FROM UNBALANCED OUT

TERMINAL STRIP

(+) = HIGH

(-) = NOT USED

= GROUND

BALANCED OUTPUT

(TYPICAL OF SYMETRIX PRODUCTS)

FEMALE XLR

PIN 2 = HIGH

TO UNBALANCED IN FROM

TIP

RING

SLEEVE

2
3

1

TRANSFORMER COUPLED OR

FLOATING BALANCED OUTPUT

TO BALANCED IN

TIP

RING

SLEEVE

TO BALANCED IN

TO UNBALANCED IN

MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +

LOW

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

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

= GROUND

MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +

LOW

REV-B

Figure 9-1. Input and output connector wiring. These diagrams represent the majority of connectors used in
modern audio equipment. Locate the source connector in the left column and match it up with the destination
connector in the right column. Wire your cable according to the diagrams.

LIN

OUTPUT STAGE

UNBALANCED

OUTPUT

INPUT

EQUALIZER

OUTPUT

Return

EXPANDER/COMPRESSOR

SIDECHAIN

OUTPUTINPUT

TIP=RETURN
RING=SEND

Return
Send

OUTPUT INPUTINPUT

PRE-AMPDE-ESS

STAGE

OUTPUT

Ground

EQ

(from EQ output)

Send

(to EQ input)

Figure 9-2. Sidechain insert jack connections

528E

35

Troubleshooting Chapter 10

Troubleshooting Chart

SYMPTOM PROBABLE CAUSE

No output Check cables and connections.

Are inputs driven by outputs, and outputs driving inputs?
Verify cables, source and load by patching input and output

connections together at the unit.
Check for AC power presence. Power LED on?
Check output by plugging headphones into output connector

(use an adapter).
Are the LED displays operating?
Is the 528E set for mic-level output?
Is the MIC/LINE switch set correctly?

Hum or buzz in output Check input and output connector wiring (refer to Figure 9-1).

Ground loop. Check related system equipment grounding. Are
all system components on the same AC ground?

Distortion Check input signal. Is it too hot, or is it already distorted?

Is the OUTPUT display indicating clipping?
Is the input clipping?
Check output loading. Should be above 600 ohms?
Are the power amplifiers clipping?
Is something else clipping?
Is the 528E set for mic-level output, driving a line-level input,

with the 528E’s gain set fairly high and upstream devices
contributing a significant amount of gain?

Noise (hiss) Check input signal levels and level control settings.

The OUTPUT display should indicate signal up to but not
including the CLIP LED.

Check gain settings on upstream equipment.
Is the input signal already noisy?
The system gain structure should be such that the 528E

operates at or near unity.
Is the 528E set for mic-level output, driving a line-level input,

with the 528E’s gain set fairly high and upstream devices
contributing a significant amount of gain?

No LED displays Is the unit plugged in and turned on?

Is the AC outlet OK?

No nothing If you are using a condenser microphone, is the phantom

power switched on?
Do you have the proper input selected?
Is everything downstream really live?
If you are using the patching jacks, unpatch everything

temporarily to see if it is in your patch.
Is the DOWNWARD EXPANDER THRESHOLD set too high?

528E

36

528E Specifications

SpecificationsChapter 11

Inputs

Controls and Switches Mic Gain, Phantom Power, Mic/Line
Mic and Line Input Connectors XLR-female (2)
Clip LED Fires at +17 dBu output level

Microphone Input Type Balanced Transformerless,
Phantom Power (DIN 45 596) +48V, nominal

Microphone Preamp Gain 22 to 60 dB (pad out),
Microphone Input Maximum Input Level -3 dBu (pad out)

Equivalent Input Noise (EIN) -126 dBV (150-Ohm source,
THD+Noise (Preamp only) 0.05% (2 kHz, 50 dB gain,
Mic Preamp CMRR > 50 dB (20 Hz to 20 kHz)

Line Input Type and Impedance 10 kilohm Transformerless
Line Input Maximum Input Level +24 dBu

Line Input Nominal Input Level +4 dBu
Line Input CMRR > 50 dB (0 dBu, 20 Hz to 20 kHz)

Parametric Equalizer

Type Three-band Parametric Equalizer
Bands Low: 16 to 500 Hz, Mid: 160 to 6300 Hz

Peak/Dip Bandwidth 0.3 to 4 octaves, measured at
Maximum Boost/Cut ±15 dB

Metering

Type Multi-segment LED bar graph
Output Level -20 to +3 VU (0 VU = +4 dBu), VU calibrated,

Gain Reduction Separate displays for:

from mic preamp or line input amplifier

Low Impedance

7 to 45 dB(pad in)

20 Hz to 20 kHz)
+17 dBu output)

Balanced Bridging

High: 680 Hz to 22 kHz

maximum boost

peak responding

de-esser, downward expander,

and compressor

0 to 20 dB per display

Overall Performance Data

Frequency Response 20 Hz to 20 kHz (+0, -0.5 dB), EQ out

THD+Noise 0.05%, 20 Hz to 20 kHz, +4 dBm output
Noise Floor Better than -89 dBu, 20-22 kHz

Dynamic Range Processor

Type Interactive Comp/Limiter-Downward Expander
Comp/Limiter Ratio 1:1 to 10:1
Downward Expansion Ratio (max) 1:1.8
De-esser Type Program controlled high-cut filter, 12 dB/octave
Frequency Range 800 Hz to 8000 Hz
Threshold -30 to 0 dBu
Output Section Type Balanced, Transformerless
Maximum Output Level +24 dBm Balanced, +18 dBm Unbalanced
Connector XLR-male
Output Clip LED Fires 3 dB below clipping
Output Source Impedance 200 Ohms, balanced
Minimum Load Impedance 600 Ohms Balanced or Unbalanced
Voice Symmetry Switch Improves modulation symmetry

Output Gain ±15 dB

Physical

Size (hwd) 1.72 x 19 x 7.25 inches,
Weight 7.6 lbs (3.5kg) net, 10 lbs (4.6kg) shipping

Electrical

Power Requirements 117V nominal, 105 to 125V AC,

230V nominal, 205 to 253V AC, 50 Hz, 15 watts maximum

Note The maximum operating ambient temperature is 25 degrees C.

Specifications subject to change without notice.

compressor out, downward

expander out, de-esser out

of speech signals

4.37 x 48.26 x 18.415 centimeters

50 to 60 Hz, 15 watts maximum

528E

37

528E Architects and Engineers Specifications

The voice processor shall be capable of all signal processing functions commonly found on a
mixing console input channel, including microphone signal preamplification, line input buffering,
simultaneous de-essing, downward expansion, compression/limiting, and parametric equalization.

The unit shall have a low-noise, low distortion microphone preamplifier with variable gain (22 dB
to 60 dB) and switchable (on/off) +48V phantom power. A 15 dB pad shall be provided to
accommodate high output microphone signals. A balanced-bridging line input suitable for +4 dBu
input signals shall also be provided along with a switch to select either the microphone or line
inputs.

The voice processor shall have an integral de-esser which shall offer up to 20 db of attenuation
within a manually sweepable frequency range of 800 Hz to 8 kHz. There shall be front panel
controls for range, frequency, and a bypass switch.

The dynamics processing section shall contain an interactive compressor/limiter and downward
expander. There shall be front panel controls for compression ratio (1:1 to 10:1), compressor
threshold (-50 dBm to +20 dBm), expander threshold (-30 dBm to 0 dBm), and a bypass switch.

There shall be a three-band parametric equalizer. Each band shall have ±15 dB maximum boost/
cut, and continuously variable bandwidth (.3 octaves to 4 octaves). The equalizer bands shall have
substantially overlapping frequency ranges, with a combined range of 16 Hz to 22 kHz. There
shall be a front panel bypass switch.

The voice processor shall be equipped with the following LED displays: An eight-segment LED
display shall be provided for monitoring the overall output level, six-segment displays for monitor­ing the de-esser, compressor/limiter, and downward expander. All displays shall be independent.
There shall also be a single LED clip indicator to indicate clipping within either of the input
preamplifiers or buffers.

The microphone input shall be an active balanced bridging design terminated with 3-pin XLR­female connector (AES/IEC standard wiring). The microphone preamp shall be capable of an
equivalent input noise specification of at least -126 dBu (150-Ohm source, 60 dB gain, 20 Hz to
20 kHz). The line input shall be a balanced, transformerless design using a 3-pin XLR-female
connector (AES/IEC standard wiring). All input circuitry shall incorporate RFI filters of the LC
low-pass type.

The output shall be an active balanced design terminated with a 3-pin XLR-male connector (AES/
IEC standard wiring). The output signal level shall be switchable to accommodate subsequent line
or microphone inputs. The output section shall provide a switchable phase rotator for the purpose
of improving the asymmetry of speech waveforms.

Access to the dynamics processing sidechain shall be provided via a ¼" TRS jack. Access to the
interstage connections between all processing sections (mic/line preamp, de-esser, compressor/
limiter/downward expander, equalizer, output stage) shall be provided via half-normalled tip-ring­sleeve (TRS) jacks.

The voice processor shall be capable of operating by means of its own built-in power supply
connected to 117V AC nominal (105 to 130V), 50/60 Hz or 230V AC nominal (207 to 253V ),
50 Hz.

The unit shall be a Symetrix Incorporated model 528E Voice Processor.

528E

38

Warranty & ServiceChapter 12

Warranty

Following are the terms and limitations of the Symetrix
warranty.

Symetrix, Inc. expressly warrants to the original
purchaser ( Buyer ), subject to the terms and
conditions set forth below, that the Product will be free
from defects in material and workmanship as a result
of normal commercial use for (18) months from the
date of shipment.

Some Symetrix products contain embedded software
and may also be accompanied by control software
intended to be run on a personal computer. Said
software is specifically excluded from this warranty.

Symetrix's warranty obligation is limited to the repair,
replacement, or refund at Symetrix's sole discretion, of
the part or parts of the Product which may thus prove
defective in materials or workmanship within one year
from date of purchase under normal use and which our
examination discloses to our satisfaction to be thus
defective, provided that Buyer gives Symetrix prompt
notice of its warranty claim and satisfactory proof
thereof.

Symetrix will make every reasonable effort to ensure
that parts are available to support the repair of our
products under warranty. In the event that a product or
component part thereof becomes obsolete, unavailable
or irreparable, Symetrix reserves the right to refund a
prorated portion of the purchase price in full satisfac­tion of all warranty claims.

In order to serve you better we require that the Buyer
shall, prior to shipping Product to Symetrix for warranty
service, contact Symetrix and secure a Return
Authorization Number that shall be included with the
returned Product. This will facilitate our efforts to keep
track of your Product and process your warranty repair
as quickly as possible. Buyer will prepay all freight
charges to ship the Product to Symetrix for warranty
inspection and service. This warranty is subject to
Symetrix's inspection of the Product at its facilities and,
upon Symetrix's request, satisfactory proof of purchase
(dated copy of original retail dealer's invoice.)

Symetrix reserves the right to effect repairs to the
product with reconditioned components/parts.
Products once repaired under warranty will be shipped
to Buyer freight prepaid by Symetrix via United Parcel
Service (surface) or any similar shipper, to any location
designated by buyer within the Continental United
States. At Buyer's request and expense Product will be
returned via airfreight. Outside the continental United
States, repaired or replaced products will be returned
freight collect.

AUTHORIZE ANY OTHER PERSON TO ASSUME
FOR US, ANY OTHER LIABILITY IN CONNECTION
WITH THE SALE OF THE PRODUCT. THIS WAR­RANTY SHALL NOT APPLY TO THIS PRODUCT OR
ANY PART THERE OF WHICH HAS BEEN SUBJECT
TO ACCIDENT, NEGLIGENCE, ALTERATION,
ABUSE, OR MISUSE. WE MAKE NO WARRANTY
WHATSOEVER IN RESPECT TO ACCESSORIES OR
PARTS NOT SUPPLIED BY US. THE TERM

ORIGINAL PURCHASER, AS USED IN THIS
WARRANTY SHALL BE DEEMED TO MEAN THAT
PERSON OR COMPANY THAT ORIGINALLY
PURCHASED THE PRODUCT.

This Symetrix product has been designed and
manufactured for use in professional/industrial systems
and is not intended for other usage. This warranty only
applies to Buyers using the Product in professional/
industrial systems. With respect to others, including but
not limited to consumers for personal, family, or
household use, Symetrix expressly disclaims all
warranties, including but not limited to warranties of
merchantability and fitness for a particular purpose and
the express warranties as otherwise provided herein.

Symetrix reserves the right to modify the design or
make additions to, or improvements to, its product lines
without making similar upgrades to Product purchased
by Buyer. Symetrix does not authorize any third party,
including any dealer or sales representative, to assume
any liability, effect any repairs or modifications to the
Product, or make any additional warranties or
representation regarding the Product or Product
information on behalf of Symetrix.

Symetrix's total liability 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 Product will not exceed the purchase price of the
Product or any part thereof which gives rise to the
claim. In no event will Symetrix be liable for any
incidental or consequential damages including but not
limited to damage for lost 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 as a result of Product failure.

This limited warranty gives Buyer certain rights. Buyer
may have additional rights under applicable law.

THIS WARRANTY IS EXPRESSLY IN LIEU OF ALL
OTHER WARRANTIES EXPRESS OR IMPLIED,
ARISING BY LAW OR OTHERWISE (INCLUDING,
WITHOUT LIMITATION ANY OBLIGATIONS OF THE
SELLER WITH RESPECT TO CONSEQUENTIAL
DAMAGES) INCLUDING THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR USE AND
OF ALL OTHER OBLIGATIONS OR LIABILITIES ON
OUR PART, AND WE NEITHER ASSUME, NOR

528E

39

Where to Get Service

If outside of the USA

If you have determined that your 528E
requires repair services and you live outside of
the United States, please contact your local
Symetrix dealer or distributor for instructions
on how to obtain service.

If inside the USA

Symetrix will perform in-warranty or out-of­warranty service on any product it has manu­factured for a period of three years from date of

discontinued manufacture. If you reside in the
USA, then proceed as follows:

In-Warranty Repairs

Repairs made in-warranty will cost you only
one-way freight charges. We'll prepay the
return (surface) freight. Of course, if the repair
is due to operator error, parts and labor will be
charged. If there are charges for the repair
costs, you will pay for the return freight. All
charges will be COD unless you have made
other arrangements (prepaid, Visa, or
MasterCard).

3 Write the RA number on the outside of

the box.

4 Ship the unit to Symetrix, freight prepaid.

We do not accept freight collect ship­ments.

Symetrix, Inc.

6408 216th St. SW

Mountlake Terrace, WA 98043

If You Don’t Have Factory Packaging
Materials

If you send us your product in substandard
packaging, we will charge you for factory
shipping materials. If you don't have the
factory packaging materials, do the following:

1 Select an oversized carton.

2 Wrap the unit in a plastic bag, and

surround it with bubble-wrap.

3 Pack the box full of Styrofoam peanuts.

Be sure there is enough clearance in the
carton to protect the rack ears.

We will return the unit in Symetrix packaging.

Out-of-Warranty Repairs

If the warranty period has passed, you'll be
billed for all necessary parts, labor, packaging
materials, and freight charges.

To Get Your 528E Unit Repaired
(USA Customers Only)

1 Call our Technical Services Group for a

return authorization (RA) number.

[phone],
Monday through Friday,

8:00 am to 4:30 pm Pacific Time.

Have your serial number ready to give to
the service representative.

2 Pack the unit in its original packaging

materials.

Include your name, address, daytime
telephone number, and a brief statement of
the problem.

528E

40

Appendix A Disassembly Instructions and Output Level Switch

Caution These servicing instructions are for use by qualified personnel only. To avoid

electric shock do not perform any servicing other than that contained in the
operating instructions portion of this manual unless you are qualified to do so.
Refer all servicing to qualified service personnel.

Warning Lethal voltages are present inside the chassis. Perform all service work with the

unit disconnected from all AC power.

Tools Required

#2 phillips-head screwdriver.

Top Cover Removal

1. Ensure that the 528E is disconnected from the AC power source.

2. Remove two 6-32 x 1/2 inch flat-head screws from the top panel.

3. Remove three 6-32 x 1/2 inch screws from each side of the chassis.

4. Lift the top cover free of the chassis.

Changing the XLR Output to Microphone-Level

The 528E ships from Symetrix with the XLR output configured for a line-level output. If you must
have a microphone-level output, get our your soldering iron. The following steps lead you through
the process of converting the line-level output to microphone-level.

1. Disconnect power from the 528E.

2. Remove the top cover.

3. Locate the XLR output connector.

4. Find the “Output Level” solder pads J17 and J18 directly behind the XLR connector.

5. Fill the space between the J17 pads with solder.

6. Fill the space between the J18 pads with solder.

7. Locate the two circuit board traces next to J18 marked by the word “Cut”.

8. Cut these two traces with a small, sharp knife.

9. Replace the top cover.

10. Reinstall the 528E and connect the input and output connectors.

528E

41

Declaration of Conformity Appendix B

Declaration of Conformity

We, Symetrix Inc.,

6408 216th St. SW, Mountlake Terrace, Washington, USA,

declare under our sole responsibility that the product:

528E 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 55103-2

Electromagnetic compatibility - Generic immunity standard

Part 1: Residential, commercial, and light industry.

The technical construction file is maintained at:

Symetrix, Inc.

6408 216th St. SW

Mountlake Terrace, WA, 98043

USA

The authorized representative located within the European Community is:

World Marketing Associates

P.O. Box 100

St. Austell, Cornwall, PL26 6YU, U.K.

Date of issue: March 15, 1999

Place of issue:Mountlake Terrace, Washington, USA

Authorized signature:

Dane Butcher, President, Symetrix Incorporated.

528E

42

528E

43

528E

44

Symetrix, Inc.

6408 216th St. SW

Mountlake Terrace, WA, 98043

USA

Tel: [phone]

Fax: [phone]

Web site: www.symetrixaudio.com

Email: [e-mail]