Symetrix 528 - Downward Expander, Compressor;Limiter Function

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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.
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