7.5

15 Using AudioSuite Plug-Ins
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Compressor AudioSuite Plug-In
The Compressor plug-in reduces the dynamic range of signals that exceed a selected
threshold by a specific amount. The increase of input signal needed to cause a 1-dB increase
in the output signal of the compressor is called the compression ratio. With a ratio of 4:1, for
example, an 8-dB increase of input produces a 2-dB increase in the output.
Audio material often varies in loudness, and can be above the threshold at one moment and
below it the next. The Attack slider sets the Compressor’s response time, or attack. The
Release slider sets the amount of time that it takes for the Compressor’s gain to return to its
original level.
To use compression most effectively:
• Set the attack time so that signals exceed the threshold level long enough to cause an
increase in the average level. This helps to ensure that gain reduction doesn’t decrease
the overall volume.
• Set release times long enough so that if signal levels repeatedly rise above the threshold,
they cause gain reduction only once. If the release time is too long, a loud section of the
audio material could cause gain reduction that persists through a soft section. Of course,
compression has many creative uses that break these rules.
• Use the Compressor’s built-in metering that allows you to monitor the amount of gain
reduction taking place. The Gain Reduction meter usually remains at 0-dB level when
the input signal is below the threshold, and falls to the left to show the amount of gain
reduction in decibels when the input signal exceeds the threshold.
The following table lists the Compressor plug-in parameters.
Parameter Description
Input Indicates the level of the unprocessed input signal to the Compressor.
Output Indicates the output level of the Compressor, including any gain compensation added through
the Gain parameter.
Reduction Indicates the amount of gain reduction in dB.
Gain Provides overall output gain adjustment. It allows you to compensate for heavily compressed
signals.
Threshold Allows you to set the threshold level. Signals that exceed this level are compressed. Signals
that are below it are unaffected. A level setting of 0 dB is equivalent to no compression. Unlike
scales on analog compressors, metering scales on a digital device reflect a 0-dB value, which
indicates full scale (FS) — the full-code signal level. There is no headroom above 0 dB.