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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.
