There are two main use for sidechain compression, the first is as an effect, where you have extreme pumping and off beat feel. The second use is to clear up your mix. When you have two instruments competing for the same space, such as a kick and a bass, you can use sidechaining to attenuate one and let the other one breathe.
What is sidechain compression?
Sidechain compression is where you trigger the compressor on one track from a signal from another track.
I will use three tracks, the 1st is a kick drum, 2nd is a snare and the 3rd is a bass line.
The first thing I do is add a compressor to the bass track then set my sidechain up, by going to the side chain box and clicking on the key button. What this does is it tells the compressor, external signal to trigger the compression. Now I need to tell it where to get the key signal from. To do that, I will set the key input over to bus 1, which will carry my kick signal over, and use that to trigger the compressor.
Now I need to set up a send on the kick drum track to bus 1 and raise the volume to unity. Set the send to pre-fader, what this means is if I mute the kick drum track or solo the bass track, I won’t lose the key input for the compressor.
After soloing the bass track, I noticed a click from listening to it at the very beginning. So I edited by cutting the first transient and moving it forward like so…
After doing that I moved every bass note up slightly and it worked no more click. So let’s play that…without the compressor…
it sort of sounds like the kick drum is scooping out ever so slightly from the bass track.
If you look at the peaks, of the compressed they are more rounded off instead of sharp to let the kick drum breathe through. Also sort of leveled off too.
Now lets here it with the kick drum and snare without compression…
Now with compression…
What is called ducking, I have made the bass stand out more prominently. Where there are bass notes the kick drum is turned down, but the release is longer. Ducking the kick behind the bassline.