LinPlug Spectral - Manual (Page 59)

ratio can be set anywhere between 1:1 (no compression) and 10:1 (heavy
compression).
The Threshold dial is used to set the signal level at which the Compressor
begins operating. The Threshold dial has a range of -24 to 0dB and
automatically adjusts the make-up Gain to give 0dB signal peaks.
The Attack dial is used to set how quickly the compressor responds to
changes in the input signal. This parameter can be adjusted with 0.1 ms
accuracy, its range is 0 to 400.0 milliseconds.
The Release dial sets the amount of time that it takes for the compressor to
return to unity gain after the signal falls below the Threshold level. The
Release time has a range of 1 millisecond to 4 seconds.
The Spectral's compressor features an Auto-Make-Up-Gain, which adjusts
the Volume so that a input of 0 dB Volume will result in an output of 0dB.
However, when you feed in significantly lower or higher signal levels you
might want to manually adjust the volume with the Volume control.