LA Audio GCX20 - Manual (Page 13)

Page 13
5.0 APPLICATIONS
5.1 COMPRESSOR APPLICATIONS
A compressor works by applying increasing levels of attenuation
(compression) to signals which exceed a set volume level. The level above
which the compression occurs is called the Threshold and the amount by
which the signal is compressed is governed by the Ratio. For example -
With an input signal at nominal level (+4dB or -10dB according to which
input connector is used), Threshold set to -10dB and Ratio set to 2:1, the
signal will be compressed by 5dB. And the RATIO setting of 2:1 ratio
means that for every 2dB the input signal increases above the Threshold,
the output will increase by only 1dB.
By enabling low level signals to be increased without a corresponding
increase in the high level signals, a compressor is able to increase the
average sound level without risk of high level distortion. This fundamental
principle of compression can be used for many applications.
Limiting PA systems
This is a basic application of compression as described above known as
limiting. Inserting the GCX20 compressor before the main PA amplifiers
will allow the system to be driven harder without driving the amp into
clipping, producing unpleasant and damaging distortion. In this application
it is necessary to apply high degrees of compression at a high Threshold
level.
Set the RATIO to 10:1 or 20:1. Set the THRESHOLD to minimum
sensitivity (fully CW). Reduce the THRESHOLD until around 15-20dB of
compression is achieved (around 3dB below the amplifier clipping point).
N.B Compressing program material with a high energy bass beat can
result in the beat triggering rhythmic compression or 'pumping'.
To avoid this effect use an external Hi pass filter in the Sidechain insert set
to around 200-300Hz. This prevents the low frequencies from dominating
the amount of compression.
Preventing tape and digital overload
Analogue tape is quite tolerant to overloading, producing its own tape
compression effect. However sending too much level to tape will result in
tape saturation distortion and track bleeding. This can be effectively
controlled with the GCX20 .
Use the GCX20s compressor with a RATIO setting of 10:1 or higher and
THRESHOLD set to produce compression just below clipping.
Digital recorders, although handling a much wider dynamic range, are
highly intolerant to excessive levels and produce unpleasant distortion
when overdriven.
Use a RATIO of 20:1 and THRESHOLD set to reduce signal levels just
before the recorder reaches clipping. Start with AUTO set to fast mode.