This is a post by mastering engineer Barry Gardner who operates
SAS Mastering What is side chain processing? Side chain
compression is often seen as a complicated production technique
but assuming you understand the basics of compression there
should not be any troubles understanding how it works. Most
audio compressors work by controlling the input signal using the
same signals dynamics, so for example when there is a loud
section in a vocal recording the peak in the vocal gets reduced
in volume. This has the effect of evening out the level of the
singing. It is a very common and useful technique for many types
of instrument and most modern music mixes will have a reasonable
amount of compression occurring. Side chain compression requires
that any given compressor has what is known as a side chain
input, key input or external key. This is a hardware or software
facility which allows the compressors detector circuit to be
controlled by an external signal other than the one that is
being compressed. Side chain