8-410 July 1998
Compressor
Figure 8-2
Compressor component.
A compressor (see Figure 8-2) is used in situations where the input
signal has a greater dynamic range, or ratio of loudest to softest, than is
desired in the output signal. Compression is accomplished by preventing
the output signal from changing in level as much as the input signal, and
can be thought of as a form of automatic gain riding.
Familiar Controls
Most of the controls in the ISP-100 Compressor are common to
nearly all traditional dynamic range compressors. These controls
should be familiar to anyone with experience in the operation of any
compressor.
Compression Ratio
The Compression Ratio control adjusts the amount by which the
output signal level changes for a given change in input signal
level. When compressing, the output level change in dB will be
equal to the input level change in dB divided by the compression
ratio:
rationcompressio
changelevelinput
changeleveloutput =
For example, if the compression ratio is 2:1 and the input level
changes by +10 dB, then:
dB5
2
dB10
rationcompressio
changelevelinput
changeleveloutput +=
+
==
Any compressor is essentially a limiter once the compression
ratio is increased beyond approximately 6:1.
Compression Ratio is selectable from {1.2:1, 1.5:1, 2:1, 3:1, 4:1,
6:1, 8:1, 12:1, 16:1, 24:1}, though any compressor is essentially
a limiter once the compression ratio is increased beyond
approximately 6:1.
Threshold
The Threshold control adjusts the input signal level above which
compression is used. When the input signal level is below the