Symetrix SX208 User manual

Symetrix
SX208
STEREO
COMPRESSOR/LIMITER
User Manual
Ver, 1.0 Ocl. 1, 1990
Seville, WAiiBtOS
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«iSymc»h April 1992

Foreword
Thankyou for purchasingthe Symetrix SX208.
The following Information In this manual may
help you achieve optimum performance from
your Stereo Compressor/Llmlter.
Even If you are very experienced with signal
processing equipment and techniques, we
encourage you to read and make use of this
manual.
Anycommentsonourproductsorthlsmanual
are more thsui welcome.

Table of Contents
Section Page
1. Introduction 1
1.1 Product Description 1
1.2 Dynamic Range 1
1.3 Threshold 2
1.4 Compression and Limiting 2
2Connections, Controls and Switches 4
2.1 Block Diagram 4
2.2 Rear Panel Connections 5
2.3 Front Panel Controls and SwHches 6
3. Troubleshooting 8
4. Service Information 9
4.1 Return Aulhodzallon 9
4.2 ln*warranty Repair 9
4.3 Out-ot-warranty Reapair 9
5. SX208 Specifications 10
6. Limited Warranty 11
7. PCS Layout 12
8. 8X208 Schematics 13
-u-

1. Introduction
1.1
Product
Description
Tlie Symetrix SX208 Stereo Compressor/
LimiterIs aprecision dynamic range controller
Intended for use In professional audio applica-
tions.
Four front panel controls, and aprecise 3LED
threshold Indicator allow signal manipulation
to solve problems found in both studio and live
environments, while retaining ease of opera-
tion. Balanced or unbalanced signals may be
applied to the 1/4“ TRS InputJacks. Outputs
may be utilized as balanced or unbalsunced
signal connections.
The heart of the SX208 is built around an
industiy standard high peifonnance VGA en-
abling adynamic range In excess of llOdB
with atypical distortion of less than .03%.
Paging systems, recording, broadcast and re-
inforcement sound ^sterns are Just afew of
the areas where the Symetrix SX208 will ofler
flawless transparent operation handling awide
variety of gain reduction tasks.
1.2
Dynamic
Range
When dealing with audio signals, the term
“dynamic range" describes actual level
changes, or the range over which signals
fluctuate. The dynamic range of the human
voice, from a wisper to ashout Is well over
lOOdB. So amicrophone will convert the
sound pressure of avoice going from a wisper
to ashout Into an electrical output signalwith
adynamic range of well over lOOdB.
For signals to stay below distortion and above
noise, their actual dynamic range must be
kept within the speclfled dynamic range ofthe
circuits through which those signals flow.
Unfortunately, the actual dynamic range of
1

real world signals often exceed the available
dynamic range of even the best equipment.
1.3
Threshold
1.4
Compression
&Limiting
The dynamic range of the best analog record-
ers Is around 70dB; still not quite enough
room for very wide dynamic range signals. In
order to keep the signals going to the recorder
well above its noise floor, and at the same time
not exceed It’s limit before distortion occurs,
signal processing Is sometimes neccessaiy to
"squeeze" the signal Into that slgnal-to-nolse
"window."
Often. In order to place high dynamic range
signals into acircuit ofnormal dynamic range
capability, acompressor or limiter Is used to
reduce signal dynamic range by setting an
upper limit on the signal peaks.
The threshold is the level at which adynamic
range processor’s activity begins. In opera-
tion, the dynamic range processor’s sensing
clcuitry constantly "looks at" the incoming
signal and compares It to areference level,
which Is called the threshold point. Compres-
sors and limiters respond when signals are
above threshold. The threshold point of the
SX208 Is internally set at -lOdB.
Compression and limiting are both derived
from the same signal processing famlty ofgain
reduction. The heart of this process Is based
on amplifier circuitry in which the gain Is
dependent on the signal level passing through
it. These ampUflers are knownasVGA's(Voltage
Controlled Ampllfler). By changing the gain,
based onsignal conditions, the dynamic range
of that signal can be automatically altered.
2
The amountofgainreductionIs determinedby
the RATIO control. The ratio is the number of
declbles ofchange in the Input level, compared