Reference Manual
CHAPTER 21. LIVE AUDIO EFFECT REFERENCE 289
21.7 Compressor
The Compressor Effect.
A compressor reduces gain for signals above a user-settable threshold. Compression re-
duces the levels of peaks, opening up more headroom and allowing the overall signal level
to be turned up. This gives the signal a higher average level, resulting in a sound that is
subjectively louder and punchier than an uncompressed signal.
The latest incarnation of the Compressor effect merges the functionality of the former
Compressor I and Compressor II devices into a single unit, and adds additional functionality
such as external sidechaining, adjustable knee, more EQ options, an improved peak mode,
and a new feedback model, which is lovingly based on some classic hardware compressors.
The new Compressor is fully backward-compatible with Compressor I and Compressor II
presets.
A compressor's two most important parameters are the Threshold and the compression
Ratio:
The Threshold slider sets where compression begins. Signals above the threshold are
attenuated by an amount specied by the Ratio parameter, which sets the ratio between
the input and output signal. For example, with a compression ratio of 3, if a signal above
the threshold increases by 3 dB, the compressor output will increase by only 1 dB. If a signal
above the threshold increases by 6 dB, then the output will increase by only 2 dB. A ratio of
1 means no compression, regardless of the threshold.
The Knee control adjusts how gradually or abruptly compression occurs as the threshold
is approached. With a setting of 0 dB, no compression is applied to signals below the
threshold, and full compression is applied to any signal at or above the threshold. With very