Glenn Fricker has posted a super-useful introduction to sidechain compression, as part of his Audio Basics series:
Sidechain compression is one of those audio mixing techniques that makes a huge difference to your own recordings. As Glenn explains, it’s used to make a bit of space in your mix whenever you have two instruments competing for the same set of frequencies.
The classic use is to carve out a space for the kick drum. The kick drum is used as a trigger for a compressor on the bass guitar. The compressor reduces the volume of the bass guitar a little bit, so that the kick drum is easier to hear.
I use sidechain compression on my guitar tracks too. I like to turn down my rhythm guitars a little bit when there’s a lead guitar part or a vocal part. I find that it makes it easier to hear the lead / vocal parts, and it helps keep the overall master output volume from jumping too much during those parts.
Please head over to YouTube to leave a like and a supportive comment if you found Glenn’s video helpful.