Symetrix 528 User manual

www.SteamPoweredRadio.Com
528 Voice Processor
Operating Manual
Revision 1.0 1 January, 1987

www.SteamPoweredRadio.Com
528 Voice Processor
Operat _g _ anual
R_ vLion LO 1 Janu ry. 1987
Symetri . ln ,c ..
4211 24, th Ave. We t
Se t le WA 98199
TI phon [phone]
elex 703282 SY RI _ UD
0
1987 Symetnx. Inc

www.SteamPoweredRadio.Com
I
I
I
I
I
I
I
FOREWORD
This manual contains all the information you need to operate the 528 Voice Processor.
There are seven chapters. The individual sections of each chapter are labeled first with
the chapter number, then with the section number. For example, the first section of the
first chapter is labeled 1. 1, and the third section of the fourth chapter is labeled 4.3,
and so on. Use the numbers referenced in the Table of Contents to quickly locate the
information you need .
IF YOU'RE GOING TO JUMP RIGHT IN AND START USING THE 528 WITHOUT READING THE
MANUAL, JUST TAKE A MINUTE TO RUN THROUGH SECTION 3 - FAST FIRST TIME SETUP.
Several different notation conventions are used to indicate various facets of the 528's
features:
CAPS
Boldface and
italics
indicate a marked feature on the 528,
like the bypass switch, or the INPUT
connector.
are · used for emphasis. Bold type
carries more weight than italic type.
Some of the text in this manual is set apart by one of the headings Note, or Caution:
NOTES convey useful information that's included to make certain functions more obvious,
and to supply extra information about processes, techniques, connectors etc.
CAUTION indicates a potential danger to the 528 or associated equipment . An example of
a CAUTION can be found below.
CAUTION
Save the oriRinal box, packinR material, and purchase receipt. If ever
it's necessary to ship your unit it must be packaRed in its original box
to prevent damage, and the receipt may be required as proof of
purchase for warranty repairs . (See Section 7.)
1

www.SteamPoweredRadio.Com
Table of Contents
1. Introduction ...................... ......... .... .............. ... .. ...... .. .............. .. .... .. ...... . 1
1.2 Microphone Preamplifier .. .......... .. . ... ...... .... .. . .................... . ..... ... .. .. .. 1
1.3 Phantom Power .......... . ..... . ...... ..... .. . .. . .... ... .. ..................... .. .... .. .... .. 1
1.4 Downward Expander, Compressor/Limiter ............................... .. ... . .... . .. 2
1.5 Defining Dynamic Range ................................................ .... .. .... ........ 3
1. 6 Dynamic Range as a Specification .... ... ........ . ...•. .. .. .. ............ ............. 3
1. 7 Dynamic Range of Sounds and Siiinals .... ... ........... .... ......................... 3
1.8 Why Dynamic Ranae Processrors are Necessary .... ........ ... .... .... ........... 4
1.9 Compressors are to Expanders as Limiters are to Gates ......... . ...... ... .... 4
1.10 The Threshold Concept ......... ..... . ...... ..... ................................ . ..... ... 4
1.11 The VCA - Voltaire Controlled Amplifier .................... . ..... . ..... . ..... ... .... 5
1.12 Linear vs. Downward Expanders ...... ..... .............................. . .......... .. . 5
1.13 How Expanders Increase Usable Dynamic Ranae .. . ................ ............... 5
1.14
Sidechain Processina .. .... .. ...... .... ... .. . ... .. .. .. ... . ........ ... ..•.................. 5
1.15
De-esser ... ... .. ............................ .. ....... ..... ...... .. ...... .. ... ... .. ............ 6
1.16
Parametric Equalizer/Notch Filter .............. .. ..... . ... .. ..... . .. ... .... . .......... 7
2.
Uaina
the 528 .................... .............. . .... .......... . ..... .. ... .. .... . .... . .... ...... . ..... 8
2.1
Gettina Started ............... ................................ ..... ....... ......... .. .... .... 8
2.2 A
Word About the Controls ................. .. .... . ..... ...... ..... .. .. .................. 8
2.3
Block Diaaram .. .. ................ ... .. .... ......... ... ..... ... ............ . ................. 9
2.4
Input/Output Connections ............ . ..... . .... .. .... . ................................. 10
2.5
Patchina / Sidechain Connections ..... ..... .. ....... ........ ...•....................... 11
2.6 Mic Preamp Controls ........ ... .. . .... .... . ....................................... .. ..... 12
2.7
De-esser Controls ... . ......... .. ..........................•........................ ... .... 12
2.8 Dynamic Range ProcessQr Controls ....••..................... . ....................... 13
2.9
Parametric Equalizer /Notch Filter Controls ...•.... .... ..... . ........ ....... ..... .. 13
2.10 Output Gain Control, Metering .. . ........................ .. ... .. . .... .... .............. 13
2.11 Installation . .. .......... .. ........... . .... •...... ......•.................................... 14
3. Faat Firat Time Setup ...... .. .. ......... ... ....................................................... 15
3.1 Connections .. ...................................... ......... . ................................ 15
3.2 Mic Preamp Setup .......................... . .. ........... . .... .. . .... . .................... 16
3.3 De-esser Setup ...... . ............. . ...... .... . ........ .... ......... .. .... . ..... .. ......... 16
3.4 Dynamic Ranae Processor Setup ... . .. .... ..... .. . .... .. ... ...... ..... . ... .. .... ...... 16
3.5 Parametric EQ/Notch Filter Setup ....... ..... .. .. .......... .. ... .. .... . ... . ........... 16
3. 6 Output Settinas ........................ . .... .. .. .... .. ... . ..... .. .. .... .. ......... .. . ...... l 6
3. 7 Meter Readings ................ ... ......... ..... ... . ..... .. ..... . ... ... ... .. ... .. ...... .. .. 16
4. Applications ............ . ............ . ........ ...... .. ............ . .... .. ... ............. .. ...... .. ... 17
4.1 Broadcast Applications ... .. .... .. .. ... .. .... .... .. ............... . ..... .. ... .. ... ... ... . 17
4 .2 Using the Parametric EQ/Notch Filter ... ......... ... ... .. .... .. ... . ... ..... .. ...... . 17
4 .2.1 Beware Distortion and Noise ... .. .... . ... . .... ... .... ........ . .... .. .... . .. ..... .. .... 17
4.2.2 Know What You Are Listenina To .. .... ... ..... . .. ...... ... .. . .... ...... . ........ ... 18
4.2.3 Use Wide Peaks, Narrow Notches ... .. . ..... .. ... .. .... ... .... .... .... .. . ........... 18
4 .2 .4 Tuning the EQ/Notch Filter .. ... ...... . .. .... :.. ..... . ......... . .......... ........ . .... 18
4.2.5 Parametric EQ/Notch Filter Examples ............................................. .. 18
4.3 Announce Mies - Compressina, Limitina, Expandina ............................ 21
4.4 Usina the De-easer ............................... .. ... . ........... . .... .... .............. 23
4. 5 Cleaning Up News Feeds .... . ..... ................. .. ............... .. .. .......... . ... .. 25
4.6 Increasing Gain Before Feedback ...... . .... ......... .. ..... .. ...... . ...... . .......... 25
4. 7 Parametric EQ in the Sidechain .... . .......... ........ ... .... .. . ...... .. . .... ......... 26
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
4.8 Usiq Sidechain EQ to Enhance Expander Action ............... .... . ......... ... 26
4.9 Usinir Reverb or Effects ..... ..... ............ . ..... ......... .. ...................... ... . 27
4.10 Vocal Processinir - Recordinir and Reinforcement ............................... 27
4.11 Addinsr Dynamics, or "Punch" .. .... ... .. .... . ...........•... ... . ... .................... 28
4.12 Hisrh Level Stasre Monitors - Dynamic Processinii ....... ... .... .. . ... .......... 28
5. 528 Speciflcationa .. ........................... ..... ................................................ 29
6. Troubleahootina Guide ..... .. ......... ... ..................... .. . ..... .... ................... ..... 30
6.1 Troubleahootinii Table .......................... ..•...... ................................ 30
7. Service Information/ Schematic• .... . ....... ......... .......... ................................ 31
7
.1 In Warranty Service . ........... ....... .... . .............. .... .. ... .... ... . ........... . .. . 31
7 .2 Out-of-Warranty Service ... ..... ....................... ......... .............. . .... ... ..31
7.3
Schematic Diallt'ams . ........... ..... .................. .. ......... ... . ............... ..... 31
7.3.1 201750B - PCB Component Placement .......... ...... ........................ .... . 32
7. 3. 2 191750B - Input Staires .............................................................. 33
7 .3.3 191750B - De-esser .. .. ........... .......... ... .. ..................................... 34
7.3.4 191750B - Compressor/Expander ............... ... . ... .... .. .................. .... . 35
7 .3.5 191750B -Parametric EQ/Notch Filter ........ ................................ . ... 36
7.3.6 191750B - Output Driver, Display, Power Supply . ..... . .................. .... . 37
7.3.7 191752A - Output Level Display .......... . ......... .. .... ..... .... . ........... .... 38
APPENDIX A - Usinii Electronically Balanced Inputs and Outputs ......................... 39
APPENDIX B - Notes on the 528-01 (Option 1 Transformer Coupled Output) ....... . .. .40
WARRANTY STATEMENT ............. ... .... ... ................... ... ............................ ..... 41
l.
iii

www.SteamPoweredRadio.Com
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
1. Microphone Signal Processors
1.1 Introduction
The 528 Voice Processor contains five functions needed for microphone signal processing:
mic preamp (with phantom power), de-esser, downward expander, compressor/limiter, and
parametric equalizer. The 528's "normal" si~al chain includes all five functions, but the
de-easer, the dynamics processor (expander/ co mpre ssor/limiter), and the parametric
EQ/notch filter may be individually bypassed with front panel switches.
In addition, the versatility of the 528 is a-reatly enhanced by its patching capabilities.
Each section is brought out to its own set of normalled rear panel terminations, so any
si~al routing possibility is provided for, and patch bay installations are supported.
1.2 Microphone Preamplifier
The ultra low noise , low distortion mic preamp provides a direct-coupled balanced input,
for optimum transient response and phase coherency. Its positive going and negative
iroinir slew rates are symmetrical, ensurinir sonic intergrity. The mic preamp's balanced
input .rain may be adjusted with the front panel gain trim control, allowing it to handle
very hi1rh signal levels -- up to -3dBV without overload.
1.3 PhantomPower
All condenser microphones require some kind of electrical power for operation. This
power may be supplied to the mic by internal batteries, an external power supply that's
connected to the microphone by a special cab le, or through the microphone cable by
phantom or "T" System powerin1r.
The 528 provides phantom powering for condenser microphones. The rear panel PHANTOM
POWER switch applies +48VDC to pins 2 and 3 at the mic input XLR connector. Phantom
power is so named because it is "invisible" to audio signals, even though the microphon e
cable carries both direct current (DC) phantom power, and alternating current (AC) audio
si~als. Specifically, the term phantom power means a positive DC volts.re applied to
the microphone via both audio leads, u sua ll y pins 2 and 3 of a 3-pin XLR type
connector. This volta.re is applied thrOUIZ'h current limiting resistors, which also serve to
isolate the audio leads from one another.
The phantom power technique uses the mic cable to deliver the power required by the
microphone , eliminatinri the need for an additional external power supply or internal
batteries. In this situation +48VDC is applied equally to both sides of a floating
balanced ci rcuit , so no current flows throurih the micr ophone's transformer, or through the
microphone element itself. However, if the circuit is unbalanced, current will flow. As
a
result, unbalan ced mies can never be used with phantom power.
Phantom powerinri is not to be confused with ''T'' System powering, sometimes called
modulation lead or AB pow erinri. ''T'' System powerinri applies power to only one audio
lead, usin1r the other as power a-round. Phantom powerin4 and 'T" Syste m powerin4 are noc
compatible without special adapters.

www.SteamPoweredRadio.Com
It is often said that the sound of some dynamic microphones is affected by phantom
power , and that ribbon mies cannot be plugged into an input that is phantom powered.
For the most part these are myths that ~ew out of difficulties that occured as a result
of some other problem in the mi c circuit:
1. When XLR connectors are ma ted there is no ~arantee that both pins 2
and 3 will make contact at exactly the same time. It is possible that a
damaging current could flow through the mic for a brief moment under these
conditions. However, this is a con-nector problem , not a problem with the
mic itself, or phantom power in particular.
2. If the mic's output transformer has developed leakage, the microphone
may become noisy (crackling, sputtering or even humming) when phantom
power is turned on. The l eakage, not the power, is the problem. The
available solutions are to tum off the phantom power, put a 1 :1 transformer
between the mic and the input, or get the mic repaired.
CAUTION
Do not use phantom power before consultin4 the microphone
manufacturer's literature. Many condenser microphones have non-
standard power requirements, and may be dama4ed by +48 volt
powerin4 . Unbalanced microphones must n ot be used with phantom
powerins.
1.4 Downward Expander, Compressor/Limiter
The 528 Voice Processor utilizes Symetrix' pro~am controlled interactive dynamic range
processing technique to combine the best attributes of both co mpressor / limiters , and
expanders. ''Pro~am controlled" means the 528's dynamic range processor section
analyzes incoming signals, then adjusts its attack and release times to match the
transient characteristics of those signals.
Levels are kept in check by the compressor/limiter, which responds quickly to transients,
and gently to normal speech level changes . The downward expander's operation is the
inverse of the comp/limiter, so it prevents "pumping" and "breathing" even when high
ratio compression is necessacy. Because the compressor/limiter and the downward
expander are interactive, the 528 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.
However, the two are often 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 vecy high ratio compressors, and gates can be
thought of as vecy high ratio expanders.
2
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
1.5 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, and
2. To define the maximum allowable range of signal fluctuations that can
be put through the equipment.
The usual unit of measure for audio signals is the decibel (dB).
1.6 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. The maximum output level is the upper limit of the
operating level, and is the level at which clipping begins . To put levels in perspective
they must be referenced to some nominal operating level, like OdBm. That's why noise
specs are stated as minus something.
In the case of the 528, noise is refered to the input, and stated as equivalent input
noise (EIN). The noise specification is ll'iven this way because the gain of the 528's
input stage is variable, so the actual signal-to-noise performance of the unit becomes a
function of how much gain is used in the preamp . To find the signal-to-noise ratio at
OdBm output, subtract the preamp gain from the EIN.
Sinoe maximum output le vel is usually lrJ'eater than OdBm, it's stated as plus something.
The 528's maximum output level is +24dBm, which is 24d8 above OdBm. The difference
between the noise floor and the onset of clipping is the dynamic range. To find the
528's dynamic ranll'e with SOdB preamp gain, subtract -87 from +24. llldB is the dynamic
range.
1.7 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 lOOdB. So a microphone will convert the
sound pressure of a the voice ll'Oing from a whisper to a shout into an electrical output
signal with a dynamic range of well over lOOdB.

www.SteamPoweredRadio.Com
1.8 Why Dynamic Range Processor s are Necessary
For siirnals to stay below distortion and above noise, their actual dynamic rani'e must be
kept within the specified dynamic rani'e of the circuits through which those siirnals flow.
Unfortunately, the actual dynamic range of real world siirnals often exceeds the available
dynamic range of even the best equipment.
For example, the dynamic range of the best analog tape recorders is around 80d8, while
dii'ital recorders top out at around 96d8. As good as these machines are, there's still
not quite enough room for very wide dynamic range siirnals. In order to maintain a 60dB
siirnal-to-noise ratio (to keep the signals 60dB above the noise floor), the dynamic range
of sipals stored on the analog tape machine would have to be restricted by 20dB, while
the digital recorder would be restricted by 36d8.
A compressor or limiter is often used to reduce dynamic range by setting an upper limit
on the lal"i'er sipals. However, in some cases it's better to put processing to work on
the lower end of the dynamic range than on the upper end. In other words, instead of
reducinir the amount of chani'e at the upper end of the dynamic rani'e with a compressor
or limiter, increasinir the amount of chanire at the lower end of the dynamic range with
an expande r or gate.
1.9 Co mpr esso rs are to Expan ders as Limiters are to Gates
Compressors reduce the dynamic range of their output whenever the input signal is above
threshold, while expanders increase the dynamic range of their output whenever the input
sipal is below threshold.
Compressors, limiters, expanders, and gates increase or decrease signal levels by some
ratio. Compressors usually have an adjustable ratio, that is, the ratio of the input level
to the output level can be changed by the user. A compressor operating with a 2:1 ratio
would allow only a ldB increase in output level for every 2dB increase in input level.
Limiters usually have a non-adjustable ratio that is very high (greater than 10:1). At
10:1, the limiter allows only a ldB increase in the output level for every l0dB increase
in the input level. Lim iters can be thought of as high ratio, high threshold compressors .
They are intended to "stay out of the way" until the level goes above threshold.
However, above threshold their action is very definite.
1. 10 The Th re sh ol d Concept
The threshold is the level at which a dynamic range processor's activity begins. In
I
I
I
I
I
I
I
I
I
I
I
I
operation, the dynamic range processor's sensing circuitry constantly "looks at" the I
incoming siirnal and compares it to a reference level, which is called the threshold
level. In practice that reference level is set by the operator with the threshold control.
Rem ember, co m pressors and limiters respond when siirnals at the input are above
threshold, while expanders and gates respond only when signals at the input are lower I
than the defined threshold.
4
I
I
I

www.SteamPoweredRadio.Com
I
I
I
I
'
I
I
I
I
1.11 The VCA -Voltage Controlled Amplifier
The action of a dynamic range processor is determined by one of the amplifier circuits
inside the unit whose gain is controlled by a DC voltage. That part of the circuit is
called a voltage controlled amplifier, or VCA. Inside the 528 a separate buffered audio
sillQal is sent to a group of circuits that comprise the detector. The detector circuits
tum the AC audio sillQal into a DC control voltage, which is sent to the VCA under the
direction of the front panel controls.
1.12 Linear vs. Downward Expanders
Expander operation is easily misunderstood unless it's remembered that what's being
expanded is the dynamics, or changes, of sillQals 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 alt changes greater by some ratio, which is
sometimes user adjustable . Linear expanders can cause distortion, because clipping
occurs when sillQals just below maximum output level are expanded.
For instance, an unprocessed sillQal 3dB below clipping that goes up 2dB won't distort,
because it's still ldB below maximum. But if that same sillQal is passed through an
expander operating at a 1:2 ratio, the same 2dB change at the expander's input would
become a 4dB change at its output. However, that sillQal would be ldB over maximum,
causi~ 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 sillQals below threshold. This gives the operator control over the
expander's activities, allowing it to be used to expand the usable dynamic range of the
system without running out of headroom.
1.13 How Expanders Increase Usable Dynamic Range
The lower limit restriction of a system is the noise floor, which is usually well below
the 528's lowest expander threshold (-60dBm) . It's important to keep in mind that while
the sillQal levels may change greatly, the noise usually doesn't change very much. The
action of the expander increases the dynamics of all signals below threshold that do
change. This action increases the apparent loudness of those changing signals, while
decreasing the apparent loudness of the noise .
For example, an expander operating at a ratio of 1:2 wilt cause a signal that falls lOdB
at its input to fall 20dB at its output. The downward action of the expander reduces th e
noise floor by the same ratio applied to the signal. Since the relationship between the
sillQal and the noise stays the same, the noise is reduced 20dB by the action of
expander, which is responding to a lOdB drop in the signal with its 1 :2 ratio.
1.14 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 528's
5

www.SteamPoweredRadio.Com
sidechain is routed through a pair of rear panel barrier strip terminations that allow the
control signal to be processed outside the unit (see Section 2.4 for specific hookup
information).
Look at the block diaiiram in section 2.3. Notice the SIDECHAIN terminations that come
fro m the comp/limit/expand section. They allow access to the control circuit that is
taken fro m the audio si1P1al at the dynamic range processor's input. This control si1P1al
is derived from, but kept totally separate from , the audio si1P1al path. That means the
contro l si1P1al can be processed outside the 528 without actually processing the signal
that's going thro u gh the VCA (the audio sigoal itself). This presents some very
interesting possibilities for changing or improving the operation of the dynamic range
processor.
The best use of the sidechain is to make the action of the 528's co m p/limiter/expander
frequency dependent, that is, to make it respond more (or less) to certain frequencies.
Beca u se the audio si1P1al and the control si1P1al remain completely separate (even while
the control circuit tells the VCA whether to tum the gain up or down), you can equalize
the sidechain without chanaing the EQ in the main audio path.
Removing unwanted frequencies from the control si1P1al before it actually reaches the VCA
prevents those frequencies from beina used to create gain changes. And perhaps most
importantly, this is accomplished without actually equalizing the signal being processed
through the 528. Applications utilizing the sidechain may be found in Section 4.
1.1 5 De-es ser
A de-easer is another type of dynamic range controller that's specially desigoed to
re2t1late hitih frequency content. The technique was originally developed for motion
pictu re dialogue recording, when it was discovered that speech sounded more natural and
pleasing when the accentuation of sibilants was reduced. By sensing and limiting
certain selected frequencies, the de-esser is intended to provide more specific control
over some of the higher frequency vocal sounds that tend to become over emphasized.
Many sibilant vocal sounds like "s," "sh," and "t" are very difficult to reproduce
electronically, because they contain a large percentage of very high frequency harmonics .
But because these sounds are so essential to the intelligibility of speech , they cannot
be simply removed with equalization. In fact, to help maintain articulation many sound
enaineers boost the higher frequencies of the vocal spectrum (3kHz to 8kHz), and / or use
microphones with "presence curves." However, in certain individuals sibilant sounds are
already over accentuated, and any kind of high frequency boost only exacerbates the
situation.
The 528's de-esse r controls excessive sibilant and fricative vocal sounds , which can
often be as much as 12dB louder than the rest of the spectrum. It's activity is similar
to a frequency conscious co m p/limiter (with an equalizer boosting the high frequencies in
its sidechain). Unlike a comp/limiter however, it operates only on the frequencies
selected. And unlike an equalizer the de-easer can reduce the offending sounds without
sacrificing intelligibility. because it operates dynamically. It removes only sounds that
are disproportionately loud, and only those that fall within the operator-selected control
range .
De-essers usually include controls that allow the ope r ator to determine which freqeunci es
are controlled, and how much those frequencies are actually attenuated. The 528's de-
6
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
'
I
I
I
I
r
I
I
I
I
I
I
I
I
I
'
esser controls are FREQUENCY, which is variable from 800Hz to 8kHz, and RANGE, which
may be set from 0dB to 20dB. In other words, the 528's de-easer will attenuate selected
frequencies between 800Hz and 8kHz as much as 20dB.
1.16 Parametric Equalizer/Notch Filter
The paramteric EQ/notch filter provides both creative and corrective frequency shapinR -
it can be used to create a more pleasinR sound, and to correct amplitude response
problems. It's desiRDed to provide an asymmetrical +l 5dB/-30dB boost/ cut response to
allow any of its three bands to perform as equalizers or hiRhly selective notch filters.
The term "parametric" simply refers to the fact that the operatinR parameters of the
equalizer may be altered. Those parameters that are user adjustable are (1) center
frequency (or fc• expressed in Hz), (2) bandwidth (sometimes called "Q," or selectivity,
expressed in octaves), and (3) the amount of cut or boost (expressed in dB).
1. Center Frequency is defined as the frequency (in Hz) at the middle of
the bell shaped response curve formed by a filter.
2. Bandwidth is the width of the bell shaped curve, measured between its
-3dB points. The measure of bandwidth in audio equalizers is usually
Riven in octaves or parts of an octave.
3. Cut or Boost is Riven in dB, at the center frequency.
7

www.SteamPoweredRadio.Com
2. Using the 528
"When all else fails, read the directions."
2.1 Getting Started
This section of your manual will give you all the control and switch settings you need
to operate the 528. Brief descriptions of the control functions are provided here, while
Section 4 includes examples of how the 528 is used, with thorough explanations of the
operation of each of the 528's processors.
IF YOU'RE GOING TO JUMP RIGHT IN AND START USING THE 528 WITHOUT READING THE
MANUAL, JUST TAKE A MINUTE TO RUN THROUGH SECTION 3 - FAST FIRST TIME SETUP .
REMEMBER, THIS ONLY NEEDS TO BE DONE ONCE TO BECOME FAMILIAR WITH THE 528'5
CONTROLS - AFTER THAT IT'S EASY .
2.2 A Word About the Controls
With its variety of functions and associated controls, the 528 can be used effectively in
a large number of situations. However, the level of performance you are able extract
from the 528 depends entirely on your understanding of the relationship between the
individual functions and controls.
2.3 Block Diagram
The functional block dia2tam in Figure 2.1 illustrates the signal flow into, inside of, and
out of the 528. Notice that the audio signal is routed through patch points between each
of the major sections , and that the sidechain of the dy namic range processor section is
available. These connections are all made on the rea r panel barrier strips TBl and TB2.
NO TB
THE UNIT WILL NOT WORK WITHOUT A COMPLETE CIRCUIT PATH
THROUGH ALL REAR PANEL PATCHING TERMINATIONS. Patching and
sidechain connections provide an output / input loop in the circuitry.
For signals to flow from the 528's mic or line input to its output,
the connection through these terminations must remain intact.
Therefore, the patching and sidechain terminations are "normalled " by
shorting straps installed at the factory. All terminal pairs that must
be normalled are indicated by "U" shaped chassis markings over the
barrier strips. The shorting straps may be removed when signals are
routed elsewhere for processing, or when individual sections of the
528 are u se d for signals not originated at the 528's input.
8
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
HlC
It-PUT r
LJ
i 2 I
LINE
INl"UT
HICIUPHCJNE
,.,.EAl'PL
If'
I
E,.
LJ
4 8
,-ATCH
LJ
8 ,
,-ATCH
-
u I
1!11
9
••
SID£
CHAIN
-
I 2 a
,-ATCH
,-Rl'tAHET,.IC
EO
NOTCH
l'ILTEl't
LJ LJ
4 8 8 1
P'ATCH
STACKING d
111
g
Ii
OUT,-UT
DOUT,.UT
I

www.SteamPoweredRadio.Com
2.4 Input/ O utput Connections
CAUTION
When the 528 is used as an input device in any system that includes
power amplifiers and loudspeakers, do not pluA into either the mic or
line inputs while the system's power amplifiers are "on." The 528 can
contribute substantial Aain to input siAnals, and very larAe low
frequency transients may be produced at the 528 ' s output when input
connections are made while the unit is "on." These transient siAnals
will not damaAe the 528 , but when amplified, may damage loudspeakers.
MIC INPUT
A 3- pin XLR connector is provided for microphone level input signals.
Pin 1 • ground Pin 2 • high (+) Pin 3 • low (-)
Input impedance is balanced bridging (to match all low impedance
professional microphones). Maximum input level is -3dBV.
+48VDC phantom power may be applied through pins 2 and 3 of the MIC
INPUT connector by depressing the rear panel PHANTOM POWER switch.
CAUTION
Do not use phantom power before consultinA the microphone
manufacturer's literature. Many condenser microphones have non -
standard power requirements , and may be damaAed by +48 volt phantom
powerinA. In addition, some dynamic microphones may be damaged by
phanto m powerinA. For more information, please refer to Section 1.3
Phanto m Power (on paAe 1).
LINB INPUT
A 1/ 4" 3-conductor TRS (Tip-Ring- S leeve) connector, which is paralleled by
barrie r strip te rm inals . Located on the rear panel , the TRS connector accepts
balanced or unbalanced signals . Use either 2-conductor ( mono type) or 3-
conductor (stereo type) connectors . As shown in the blo ck diagram in Figure
2. 1, the TRS connections are :
Tip • high (+) Ring • low (- ) Sleeve • ground (shield) .
Termi n als 1, 2 and 3 on barrier strip TBl are connected inparallel with the
1/ 4" TRS connector . Balanced or unbalanced line level input signals may
be connected here as well.
11 • high (+) 12 • low (-) 113 • ground
The balanced LINE INPUT impedance is 46.3k ohms . Unbalanced input
impedance is 23.lk ohms . Maximum input level is +18dBV.
10
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
'
'
r
STACKING INPUT
A pair of teminations on barrier strip TB2 for signals from another 528 Voice
Processor (or any other line level device). This input allows two 528's to be
operated through a single output. To stack two 528's, connect the EQ OUT
patch from one 528 to the STACKING INPUT on the other 528. (The OUTPUT GAIN
controls remain separately active, as "submasters.")
16 • ground
The STACKING INPUT impedance is > 10k ohms, maximum input level is
+18d.Bm.
OUTPUT
A
1/4" 2-conductor (mono type) TS (Tip-Sleeve) connector, which is in parallel
with the barrier strip output terminals #8 and 10. Located on the rear panel,
the the 1/ 4" connector delivers unbalanced low impedance output signals.
Tip • signal Sleeve • ground (shield).
Terminals 8, 9, and 10 on barrier strip TB2 deliver balanced output signals.
The connections are:
18 • ground 19 • low (-) 110 • high (+)
Output impedance is 51 ohms, balanced or unbalanced. Minimum load
impedance is 600 ohms. Maximum output level is +24dBm balanced, +18dBm
unbalanced.
CAUTION
When the output is operated in an unbalanced confi,uration DO NOT
,round the unused le,. Doin, so wiJJ unnecessarily load the output
driver, resultin' in increased distortion and possible dama,e. See
Appendix A - Usin, ElectronicaJJy Balanced Inputs and Outputs.
2.5 Patching/Sidechain Connections
Output/Input patching connections are provided on the rear panel barrier strips TBl and
TB2, as shown in the drawing below . All terminations are unbalanced .
PATCHING
Output impedances are all < 100 ohms, m1m1num load impedance for all patching
outputs is 600 ohms. Maximum output level is +18dBm .
Input impedances are all >20k ohms. Maximum input level is +18dBV.
11

www.SteamPoweredRadio.Com
SIDBCHAIN
The SIDECHAIN connections provide access to the dynamic range processor's
control circuit, via terminals 8, 9 and 10 on barrier strip TBl.
Output impedance of the SIDECHAIN is < 100 ohms , minumum load impedance is
600 ohms. Maximum output level is + 18 dBm. Input impedan ce is > 20k ohms,
maximum input level is +18dBV.
NOTE
Patching and sidechain connections provide an output / input loop in
the circuitry. For signals to flow from the 528's input to output, the
connection through these termina t ions must remain intact. Therefore,
the patching and sidechain terminations are "normalled" by shorting
straps installed at the factory . All terminal pairs that must be
normalled are indicated by "U" shaped chassis markings over the
barrier strips. The shorting straps may be removed when signals are
routed elsewhere for processing, or when individual sections of the
528 are used for signals not originated at the 528 ' s input.
2.6 Mic Preamp Controls
PREAMP GAIN
Sets the . gain of the microphone preamplifier, from 10 (3dB) at its most
counterclockwise rotation, to S0dB at its mo s t clockwise rotation .
CLIP
Illuminates when preamp output levels reach +16dBm.
PHANTOM POWER
On the rear panel near the line output jack, this switch turns on + 48VDC
phantom power for condenser microphones, applied v ia pins 2 and 3 of the XLR
input connector.
2.7 De-esser Controls
DB-BSS FREQUENCY
Selects the frequency range to be placed under the control of the de-esser .
DB-BSS RANGE
Determines how much the selected frequ e ncies will be attenuated . At 0dB the
de - easer is essentially out of the circui t , while at 20dB all signals within the
selected frequency range will be attenuated 20dB.
BYPASS
Enables / disables the de-esser .
12
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
2.8 Dynamic Range Processor Controls
EXPAND THRESHOLD
Sets the level below which the downward expander's activity begins.
COMPRESS THRESHOLD
Sets the level above which the compressor/limiters' activity begins.
COMPRESSION RATIO
Sets the compressor/limiter's ratio from 1.4:1 to 20:1.
BYPASS
Enables/disables the compressor/limiter/expander.
2.9 Parametric Equalizer/Notch Filter Controls
CUT/BOOST
Adjusts the cut or boost from -3 0dB to +lSdB.
BANDWIDTH
Sets the selectivity ("Q") of the equalizer, and therefore the amount of the
spectrum affected by the CUT/BOOST control. Calibrated in octaves, from .OS to
3.3 (see Section 1.12, Paramteric Equalizer/Notch Filter).
FREQUENCY
Determines which frequency lies at the center of the bell-shaped curve that
encompasses the particular frequencies affected by this band of the equalizer.
Calibrated in Hz, the LO," "MID" and "HI" sections may be overlapped.
EQ BYPASS
Switches the parametric equalizer/notch filter into or out of the circuit path.
2.10 Output Gain Control, Metering
OUTPUT GAIN
Sets the overall gain of the 528 from a minimum of -lSdB, to OdB (unity) at top
dead cente r, to a maximum of +lSdB.
OUTPUT LEVEL
lndicates the unit's output level in volume units (VU). OVU • 1.23 volts across
600 ohms (+4dBm).
CLIP
Illuminates when output levels are within 3dB of the onset of clipping .
GAIN REDUCTION
Indicates the gain reduction provided by either the dynamic range processor
section (compressor/limiter/expander), or by the de-esser section.
COMPRESS/DE-ESS
Switches the GAIN REDUCTION m eter to read the gain change at the dynamic
range processor's VCA, or the de-easer's VCA.
13

www.SteamPoweredRadio.Com
2.11 Installation
The unit is deaisrned for mountit12 in a standard 19" rack , and requires only 1
rack apace (1-3/4"). The 528's lNPUTs, OUTPUTs and SlDECHAIN connectors
should be wired to a patch bay (like the Symetrix Patch 32) for ease of
operation. A su22eated arran2ement is shown in Fi20re 2.3. The patchin2
output / input connections and the SlDECHAIN output / input connection must remain
intact when not used. When the unit i ■ wired into a patch bay, these
connection ■ mu ■ t be normalled.
CAUTION
Do not mount the 528 near hieh power devices like amplifiers and
power supplies. When the unit is rack mounted, take care to keep it as
far from bum fields as possible. Like all devices desiened to provide
bieb eain for low level sienals, the 528's microphone preamp is
sensitive to induced hum.
14
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

www.SteamPoweredRadio.Com
'
'
I
l
r
3. Fast First Time Setup
Follow this sequence to get the 528 up and running quickly - the connections and
settings are intended to get si1?11al into and out of the 528, and to create obvious
activity in each processor section. The drawings at the end of this section illustrate
the setup. FOR QUICK SETUP, DO NOT DEPRESS ANY OF THE BYPASS SWITCHES.
CAUTION
Wbea the 528 is used as an input device in any system that includes
power amplifiers and loudspeakers, do not plUR into either the mic or
line inputs while the system's power amplifiers are "on." The 528 can
contribute substaatial Raia to input siQnals, and very IarRe low
frequency transients may be produced at the 528's output when input
conaections are made while the unit is "on." These transient siRnals
wiIJ not damaRe tbe 528, but when amplified, may damaRe loudspeakers.
3.1 Connections
MIC INPUT
Plug the microphone's male XLR into this connector.
LINB INPUT
Use either the 1/4" TRS input, or terminals 1, 2 and 3 on barrier strip TBl, to
feed line level signals to the 528.
OUTPUT
Use either the 1/ 4" TS connector for an unbalanced output, or terminals 8, 9
and 10 on barrier strip TB2 for a balanced output, to feed si1?11als to the input
of the following device.
3.2 Mic Preamp Setup
PRBAMP GAIN
For dynamic mies, set the slot at "12 o'clock" (approx. 35dB gain).
For condenser mies, set the slot at "9 o'clock" (approx. 25d8 gain).
PHANTOM POWBR (rear panel)
For dynamic microphones, do not depress this switch.
For condenser microphones that require +48VDC phantom powering, depress this
switch (See Section 1.3 Phantom Power).
15