In
audio,
sidechain refers to a
signal which has branched
away from the
audio path of a device, and will not appear on the
output. It usually controls a processor which
does affect
the audio path directly.
For example, a
compressor or
gate takes a sidechain, and determines its level,
using this to control a
VCA which directly affects the output.
Amplifier
Signal |\
Audio In -----+----------------------| >------ Output
| |/
| ^
| +--------------+ |
Sidechain +---|level detector|----+
+--------------+
Some devices bring the sidechain to the
panel, to allow an
external signal to control the processor, or to have a processed sidechain sent to another device. Examples of such devices are
DBX 1066 and
BlueMAX stereo compressor, which allow a signal to be compressed according to the output of another signal.