Symetrix 528E User manual

User’s Guide
528E Voice Processor

User’s Guide
528E Voice
Processor
1/32
Before You Begin
What Ships in the Box
RA 528E hardware unit.
RA detachable power cord.
RThis User’s Guide.
Getting Help
If you have questions beyond the scope
of this User’s Guide or the help module,
contact our Customer Support Group in
the following ways:
Tel [phone]
8:00 am to 4:30 pm
Monday through Friday,
Pacific Time
Web support.symetrixaudio.com
Important Safety Instructions.
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near
water. This apparatus shall not be
exposed to dripping or splashing and
no objects filled with liquids, such as
vases, shall be placed on the appara-
tus.
6. Clean only with dry cloth.
7. Do not block any ventilation open-
ings. Install only in accordance with
the manufacturer’s instructions.
8. Do not install near any heat sources
such as radiators, heat registers,
stoves, or other apparatus (including
amplifiers) that produce heat.
9. This apparatus shall be connected
to a mains socket outlet with a
protective earthing connection. Do
not defeat the safety purpose of the
polarized or grounding-type plug. A
polarized plug has two blades with
one wider than the other. A grounding
type plug has two blades and a third
grounding prong. The wide blade or
the third prong are provided for your
safety. If the provided plug does not
fit into your outlet, consult an electri-
cian for replacement of the obsolete
outlet.
10.Protect the power cord from being
walked on or pinched particularly at
plugs, convenience receptacles, and
the point where they exit from the
apparatus.
11. Only use attachments/accessories
specified by the manufacturer.
12.Use only with the cart,
stand, tripod, bracket,
or table specified by
the manufacturer, or
sold with the apparatus.
When a cart is used, use caution
when moving the cart/apparatus com-
bination to avoid injury from tip-over.
13.Unplug this apparatus during light-
ning storms or when unused for long
periods of time.
14.Refer all servicing to qualified service
personnel. Servicing is required when
the apparatus has been damaged in
any way, such as power-supply cord
or plug cord 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.
AVIS:
NE PAS OUVRIR
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
S’adresser a un reparateur compétent.
RISQUE DE CHOC ELECTRIQUE
No user serviceable parts inside. Refer servicing to qualified service personnel.
CAUTION
WARNING:
TO REDUCE THE RISK OF FIRE OR
ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE
DO NOT OPEN
RISK OF ELECTRIC SHOCK
The lightning flash with arrowhead
symbol within an equilateral triangle is
intended to alert the user of the pres-
ence 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 User’s Guide).
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
prongs can be fully inserted.
Power Source. The 528E Voice
Processor hardware is configured at the
factory for domestic or export markets.
Ensure that your AC mains voltage
matches that of your power supply.
Refer to rear panel marking for correct
AC source voltage. Use only the power
cord and connector specified for the
product and your operating locale. A
protective ground connection, by way of
the grounding conductor in the power
cord, is essential for safe operation. The
appliance inlet and coupler shall remain
readily operable once the apparatus has
been installed.
User Serviceable Parts. There
are no user serviceable parts inside the
528E Voice Processor. In case of failure,
customers inside the U.S. should refer
all servicing to the Symetrix factory.
Customers outside the U.S. should refer
all servicing to an authorized Symetrix
distributor. Distributor contact information
is available online at
www.symetrixaudio.com.

User’s Guide
528E Voice
Processor
2/32
Introduction
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 phantom-powered 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.
Fast First Time 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 a Mic or Line level source to the appropriate input connec-
tor on the rear of the 528E. Be sure to set the Mic / Line switch to the
appropriate position and be sure to turn on phantom power if using a
microphone that requires it. Next, connect the appropriate output of the
528E to your monitoring system or mixing console. Finally, connect the
528E to an AC source of the proper voltage and frequency as marked
on the rear of the unit.
Caution: Failure to connect the 528E to the proper AC
mains voltage may cause fire and/or internal damage.
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.
If you are using a condenser microphone, refer to “Phantom Powering Condenser Microphones” before depressing the Phan-
tom Power switch.
Introduction, Fast First Time Setup
Rear Panel Connection/Setting
Output Connect to input of console,
tape recorder, etc.
Line Input Connect line-level source here.
Mic Input Connect microphone here
Phantom Power Depress if mic requires phantom
powering.

User’s Guide
528E Voice
Processor
3/32
Settings
Set the controls and switches on the front of the 528E per the following table:
Front Panel Control Setting Front Panel Control Setting
MIC / LINE As required LOW EQ FREQUENCY 160 Hz (12 o’clock)
-15 PAD Out LOW EQ BANDWIDTH 1.5 octaves (12 o’clock)
MIC GAIN 12 o’clock LOW EQ CUT/BOOST 0 (12 o’clock)
DE-ESS FREQUENCY 3K (12 o’clock) MID EQ FREQUENCY 2.5K (12 o’clock)
DE-ESS THRESHOLD 0 (Full CW) MID EQ BANDWIDTH 1.5 octaves (12 o’clock)
DE-ESS IN / OUT Out MID EQ CUT/BOOST 0 (12 o’clock)
DOWNWARD EXPANDER EXP THRES BYPASS (Full CCW) HIGH EQ FREQUENCY 6.8K (12 o’clock)
COMPRESSOR COMP THRES +20 (Full CW) HIGH EQ BANDWIDTH 1.5 octaves (12 o’clock)
COMPRESSOR COMP RATIO 2 (12 o’clock) HIGH EQ CUT/BOOST 0 (12 o’clock)
EXP/COMP IN / OUT Out EQ IN / OUT Out
VOICE SYMMETRY IN / OUT Out GAIN 0 (12 o’clock)
You can now power on the 528E and it should pass signal. The OUTPUT LEVEL LED display should show some activity and the
POWER LED should be illuminated. We can now move on to fine tuning your settings.
Mic Preamp Gain
Set the MIC GAIN control so that the OUTPUT LEVEL LED display indicates a signal between -10 and 0 VU. The CLIP LED should
almost never light. If it does, decrease the MIC GAIN control until it does not. Any loss in gain can be made up for later in the signal
chain.
De-Esser Settings
The De-Esser is used to reduce the level of objectionable sibilant sounds (S and T sounds). Engage the De-Esser by pressing the
DE-ESS IN / OUT button IN. Set the THRESHOLD control so that the de-esser gain reduction LED display shows about 12 dB of
reduction. Now, “tune” the FREQUENCY control for the maximum sibilance reduction. Finally, reduce the setting of the THRESHOLD
control until you reduce the sibilance to a tolerable level without harming the quality of the audio signal.
Downward Expander Settings
Use the Expander to reduce room noise or other low level or background noise. Set the THRESHOLD control to allow low level
speech sounds to pass while still blocking out room sound or noise.
Compressor Settings
Use the COMP THRES control to determine the level at which the compressor starts to work. As the sound level increases above the
set threshold, you will see the gain reduction LED display start to work indicating the amount of gain reduction taking place. 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 (greater than 8:1) for limiting or in-your-face sorts of sounds.
Equalizer Settings
Equalization is entirely dependent upon many factors and should generally be used to correct or enhance the frequency content of the
signal. For example, the default settings should be close for the male voice. For female voices, the LOW EQ range shifts up to 200 or
300 Hz and the MID EQ range shifts up to 3-5 kHz.
If you are using a microphone that exhibits proximity effect, then you’ll probably need to reduce (cut) the bass (LOW EQ) response
somewhat. 3-6 dB should be fine, but you’ll have to compromise between a big full sound and the overbearing low frequency content.
A bit of MID EQ will help make voices cut through and seem louder. The HIGH EQ can add brightness and intimacy.
It will take some tuning and experimentation based on the signal source, microphone used and personal taste.
Output Settings
For many applications, setting the output GAIN control to 0 dB works fine. If you are adding a lot of EQ, this will tend to cause an over-
all level increase. Thus, you may need to lower the output GAIN appropriately. Likewise, if you are using a fair amount of compres-
sion, you may need to add some gain to compensate for the gain reduction in the compressor section. You should adjust the output
GAIN control so that it provides enough signal level to your connections downstream, yet still prevents the CLIP LED from illuminating.
The output CLIP LED monitors both the equalizer and the output stage. Large amounts of EQ 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 pro-
cessor, inserted via the OUTPUT STAGE INPUT jack, is contributing gain to the overall signal path. In this case, either lower the gain
of the inserted processor or reduce the setting of the output GAIN control.
Fast First Time Setup... continued

User’s Guide
528E Voice
Processor
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Front & Rear Panel Overview
Mic Preamp
MIC/LINE Selects between the Mic input (switch in) and Line input (switch out).
-15 PAD Inserts 15 dB pad for strong mic signals.
MIC GAIN(dB) Sets the gain of the mic preamp for best compromise between signal-to-noise ratio
and headroom.
CLIP 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.
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.
DE-ESS Hard-wire bypasses the de-esser. The de-esser is active when this switch is in.
IN/OUT
LED Display Indicates the amount of de-esser activity at any instant in time.
Downward Expander / Compressor
EXP THRES Sets the threshold level for the downward expander. Signals below this threshold
are downward expanded (reduced in level).
EXPANDER Indicates the amount of de-esser activity at any instant in time.
LED Display
COMP THRES 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
COMPRESSOR Indicates the amount of compressor activity (gain reduction) at any given instant in time.
LED Display
Parametric EQ Low
FREQUENCY Varies the center frequency of the low-frequency equalizer from 16 Hz to 500 Hz.
BANDWIDTH Varies the bandwidth of the low-frequency equalizer from 0.3 to 4 octaves.
(Q = 0.27 to 4.8).
CUT/BOOST Set the degree of boost or cut +/- 15 dB.
Parametric EQ Mid
FREQUENCY Varies the center frequency of the low-frequency equalizer from 160 Hz to 6.3k Hz.
BANDWIDTH Varies the bandwidth of the low-frequency equalizer from 0.3 to 4 octaves.
(Q = 0.27 to 4.8).
CUT/BOOST Set the degree of boost or cut +/- 15 dB.
Parametric EQ High
FREQUENCY Varies the center frequency of the low-frequency equalizer
from 680 Hz to 22 kHz.
BANDWIDTH Varies the bandwidth of the low-frequency equalizer from
0.3 to 4 octaves. (Q = 0.27 to 4.8).
CUT/BOOST Set the degree of boost or cut +/- 15 dB.
EQ IN/OUT Hard-wire bypasses the entire equalizer.
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR

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528E Voice
Processor
5/32
Front & Rear Panel Overview... continued
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 correction into the signal path.
SYMMETRY
OUTPUT LED Indicates the peak output level of the 528E relative to the balanced output.
The 0 VU LED on the display corresponds to +4 dBu 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.
Power
AC INPUT IEC power connector. Connect only to appropriate AC power
source. Refer to rear panel marking for correct AC source
voltage.
POWER Turns the 528E on and off.
SWITCH
SERIAL Please note the serial number
NUMBER for future reference. Should your 528E ever require service,
Symetrix Customer Service will need this information in order to
process your repair request.
Output Stage I/O
BALANCED XLR male connector. Balanced, line level output. This output may be converted
OUTPUT to a mic level output. See Output Level Switch section.
UNBALANCED TRS phone jack (wired for unbalanced operation). Provides a line OUTPUT level
unbalanced output. This jack is unaffected by the Mic Level Output Configuration
switch mentioned above.
OUTPUT TRS phone jack (wired for unbalanced operation). This is the input to the output
STAGE INPUT stage. Inserting a connector into this jack will interrupt any signal coming from
previous (upstream) modules of the 528E.
Equalizer I/O
OUTPUT TRS phone jack (wired unbalanced). This is the output of the equalizer. Inserting a connector
into this jack does not interrupt signal flow to the 528E’s output stage.
INPUT TRS phone jack (wired unbalanced). This is the input to the equalizer. Inserting a connector
into this jack interrupts signal flow from the Expander / Compressor.
Expander/Compressor I/O
OUTPUT TRS phone jack (wired unbalanced). This is the output of the expander / compressor.
Inserting a connector into this jack does not interrupt signal flow to the equalizer.
SIDECHAIN TRS phone jack wired as an insert jack. (Tip = return, Ring = Send). Use this jack
trigger or “key” the compressor / expander from an external source.
INPUT TRS phone jack (wired unbalanced). This is the input to the expander / compressor.
Inserting a connector into this jack interrupts signal flow from the de-esser.
-15
-30
DE-ESS (-dB)
20 800 60 8K
15
CLIP
3K
0BYPASS
DE-ESS
-40
0 +20 110 16
EXP/COMP
.3500 4
9246912
-15
1220 16
-25 -10
36
2160 1.5
EQ
+15
6.3K
+15 160 .3 -15
4680 22K .3 4-15 +15
02.5K 1.5 06.8K 1.5 0
+15-15
-3-6-10-20 -15
0
CLIP30
MIC PRE-AMP
MIC GAIN(dB)
MIC
LINE
PHANTOM
IN
OUT
FREQUENCY THRESHOLD
DOWNWARD EXPANDER (-dB)
OUT
IN
EXP THRES COMP THRES COMP RATIO
HIGH EQLOW EQ
FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST FREQUENCY BANDWIDTH CUT/BOOST IN
OUT GAIN (dB)
OUTPUT LEVEL (VU)
OUT
IN
SYMMETRY
VOICE
MID EQ
20 61216 9 3
COMPRESSOR (-dB)
POWER
dBHz OCT Hz OCT dB Hz OCT dB
-15 PAD
NORM
528E
VOICE
PROCESSOR

User’s Guide
528E Voice
Processor
6/32
Front & Rear Panel Overview... continued
De-esser I/O
OUTPUT TRS phone jack (wired unbalanced). This is the output of the de-esser. Inserting a connector
into this jack does not interrupt signal flow to the 528E’s expander / compressor.
INPUT TRS phone jack (wired unbalanced). This is the input to the expander / compressor.
Inserting a connector into this jack interrupts signal flow from the mic / line inputs.
Preamp Stage I/O
PREAMP STAGE TRS phone jack (wired unbalanced). This is the output of the
OUTPUT mic / line preamp. Inserting a connector into this jack will not
interrupt signal flow to the 528E’s de-esser.
LINE INPUT XLR female connector providing a 10k Ohm balanced bridging
line input intended for signals ranging from -10 dBu to +4 dBu.
MIC INPUT XLR female connector providing a balanced input suitable for low
impedance microphones. 48V phantom powering is available at
this connector.
PHANTOM Pushbutton switch enabling 48V phantom power on the MIC INPUT.
POWER

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528E Voice
Processor
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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 section 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.
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:
To describe the actual range of signal fluctuations that are going through the equipment.
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.
Noise floor is defined as the lower limit of a circuit’s operating level, and is a function of its self-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
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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 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.
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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 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 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.
Refer to the block diagram in a later section. 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

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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 Applications section.
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 in dB).
These terms are defined as follows:
Center Frequency is defined as the frequency (in Hz) of the middle of the bell shaped response curve formed by a filter.
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.
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 octave.
Power and Fullness
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 this range. Harvey Fletcher (of Fletcher-Munson fame) charted the sensitivity of
the ear for various 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.
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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, 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

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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.
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 low-frequency response somewhat.
Some general thoughts on speech equalization:
Try to use wider bandwidths. Narrower bandwidths (1/2 octave and less) are less audible (harder to hear) and are1.

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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).
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.
A wide bandwidth cut is equivalent to a boost at the frequencies surrounding the cut.
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.
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 source-microphone 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
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.
The majority of the material in Section 2.2 is taken from “Equalizing for Spectral Character,” Langevin Corporation, 1966
Catalog.
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.
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.
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61.74
65.41
73.42
82.41
87.31
98.00
110.00
123.47
130.81
146.83
164.81
174.61
196.00
220.00
246.94
261.63
293.66
329.63
349.43
392.00
440.00
493.88
523.25
587.33
659.26
698.46
783.99
880.00
987.77
1046.50
1174.70
1318.50
1396.90
1568.00
1760.00
1975.50
2093.00
2349.30
2637.00
2793.80
3136.00
3520.00
3951.10
4186.00
4698.60
5274.00
5587.60
6272.00
7040.00
7902.20
8372.00
9393.20
10548.00
11175.20
12544.00
14080.00
15804.40
Figure 2-2. Relationships of Musical instruments, Piano, and actual frequencies.
Voice Processing Tutorial... continued

User’s Guide
528E Voice
Processor
15/32
Using the 528E
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
The block diagram below 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.
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).
•
•
•
SS E R P
R P S E S
DOWNWARD
EXPANDER
EQ
LOW
EQ
MID
OUTPUT STAGE
WITH SYMMETRY
CORRECTION CIRCUIT
OUTPUT
THUMP
MUTE
CIRCUIT
OUTPUT LEVEL
SELECTION
CIRCUIT
BALANCED
UNBALANCED
POWER
SUPPLY
EQ
HIGH
COMPRESSOR
DE-ESS
-15dB
PAD PREAMP
+48V/BYPASS IN/OUT
MIC GAIN
CLIP
FREQUENCY
EXP
THRES GAIN
COMP
THRES
COMP
RATIO
OPTIONAL
POWER SWITCH
VOICE
SYMMETRY
IN/OUT
INTERNAL
OUTPUT LEVEL
SELECT SWITCH
OUTPUT LEVEL DISPLAY
EXP/COMP
IN/OUT
THRESHOLD
DE-ESS
IN/OUT
EXP/COMP
OUTPUT
EQ
OUTPUT
EQ
INPUT
OUTPUT STAGE
INPUT
MIC
LINE
EQ
IN/OUT
FREQUENCY FREQUENCY FREQUENCY BANDWIDTH BANDWIDTH BANDWIDTH CUT/BOOST CUT/BOOST CUT/BOOST
EXPANDER/COMPRESSOR
EXTERNAL SIDECHAIN
(RING=SEND. TIP=RETURN)
EQ CLIP DETECTION
OUTPUT
OUTPUT
PHANTOM
POWER
SUPPLY

User’s Guide
528E Voice
Processor
16/32
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 switch-
ing 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.
Operational Details
This section describes the details of operating the 528E. Usage information can be found later in this section.
The 528E accepts monaural analog input signals at mic or line level, processes them, and delivers them back to you as bal-
anced 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.
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... continued
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
RP E SSSESPR

User’s Guide
528E Voice
Processor
17/32
Using the 528E... continued
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
below.
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.
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
section).
Inserting Additional Processing
The illustration shown on the next page 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:
Decide where in the signal path you wish to insert the external processor.
Patch the appropriate output jack on the 528E to the input jack of the external processor. Use either a TRS or TS patch-
cord.
Patch the output jack of the external processor to the corresponding input jack on the 528E. Use either a TRS or TS
patchcord.
1.
2.
3.
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
RP E SSSESPR

User’s Guide
528E Voice
Processor
18/32
Using the 528E... continued
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 compres-
sors, expanders, gates, equalizers, as well as the 528E, are
all series processors that don’t.
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, many engineers prefer the opposite; the com-
pressor receives the output of the equalizer. The figure right
illustrates this patch.
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. The figure right illustrates this patch. You can find
out more about using the sidechain later in the next section.
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 de-
veloping your own settings.
Metering
The 528E has several LED bargraphs that serve as gain reduction and output meters. The gain-reduction 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 understand-
ing of this topic is essential to getting the most from your 528E. A more basic discussion can be found under the heading,
“Level Setting,” in the previous section.
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 De-esser, 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
STAGE
OUTPUT
PRE-AMPDE-ESS
OUTPUT INPUTINPUT
SIDECHAIN
TIP=RETURN
RING=SEND
OUTPUTINPUT
EXPANDER/COMPRESSOR
OUTPUT
UNBALANCED
OUTPUT
OUTPUT STAGE
INPUT
EQUALIZER
EXTERNAL AUDIO PROCESSOR
INPUTOUTPUT
LIN
STAGE
OUTPUT
PRE-AMPDE-ESS
OUTPUT INPUTINPUT
SIDECHAIN
TIP=RETURN
RING=SEND
OUTPUTINPUT
EXPANDER/COMPRESSOR
OUTPUT
UNBALANCED
OUTPUT
OUTPUT STAGE
INPUT
EQUALIZER
LIN
STAGE
OUTPUT
PRE-AMPDE-ESS
OUTPUT INPUTINPUT
SIDECHAIN
TIP=RETURN
RING=SEND
OUTPUTINPUT
EXPANDER/COMPRESSOR
OUTPUT
UNBALANCED
OUTPUT
OUTPUT STAGE
INPUT
EQUALIZER
OUTPUT
INPUT
TO RING
TO TIP
WIRING NEEDED
NOTE: SPECIAL
LIN