There’s a hyperinflation of side-chain compression in popular music. And sometimes it sounds – more or less – like loose cables or dropouts. Still, used properly, side-chain compression could be the factor to a floor-filler.
So about compression, it’s a big part of today’s music. It keeps the volume levels at bay and making sure shit sounds tight. And loud (without increasing its peak amplitude). At the same time the dynamic range is reduced, and dare I say, music do tend to sound less, well, dynamic, than classics from yesterday. Whatever.
In normal compression, the incoming audio signal is used as source for the threshold and ratio. Side-chaining (or keying) is a technique that uses a different audio signal to trigger/key the compressor. Whilst the incoming audio is still affected, it’s the side-chained audio signal that determines the compressor’s response; that is, how strongly it will reduce the gain on its output signal.
The premise is basically a kick drum that triggers the compressor of a bass, i.e. bass ducking. This allows the kick through – on the same low frequencies as the bass – without phase interference or a too muddy low-end. You can get a rhythmically pumping or pulsating effect if you duck out other instruments in the mix as well.
Remember that you can have other shit than the kick to trigger the compressor. Or, if you prefer, you can even program a specific pattern for this.
It’s kinda hard to generally guide to how to achieve a side-chain compression due to the many different DAWs out there. But briefly you should rig a compressor to your bass (or mix bus), and connect a different audio source to the side-chain input. Then set the compressor to a very low threshold (around -35 dB) and a high ratio (60:1), combined with a short attack (1 ms) and a longer release time (600 ms). But go ahead and experiment with these settings, adjust to taste. Also the length of the audio source, e.g. kick drum sample, will have some affect.