So, side-chain compression. What is it and how does it work right? First of all, lets take it back a little to make sure that you understand compression first of all. There are several elements to a compressor, these include the threshold, ratio, attack, release and knee. The threshold of a compressor allows you to set which the point the compressor ‘kicks in’. The ratio then allows you to set the amount of compression you will actually get. The attack, release and knee are all tools which allow for adjustments to how quickly the compressor reacts to the signal as it approaches the threshold.
So now you know the general ins and outs of a compressor, what is the purpose of a side-chain compressor and how does side-chaining work? To summarise it, side-chaining is the process of “using the output of one track to control the action of a compressor on a completely different track” (Colletti, 2013). So the compressor is monitoring one thing and is now controlling another. When the other channel gets louder, the compressor clamps down on the channel that its applied to and the other signal comes through as louder. This diagram shows how it works on a very general scale. A compressor is put on the bass track and side-chained to the kick so that, when the kick noise comes in, the bass sound is ducked down in volume by a set amount in order to let the kick punch through.
A very simple example of this is used by a lot of DJs. It is possible for them to add a compressor to the track playing music. From here, they will side-chain this track to a microphone input. By doing so, whenever their microphone is talked into and turned on, the music volume will duck to allow for the DJ to be heard.
Side-chaining is also a very common technique used in electronic music so as to allow the kick drum to punch through the bass-line. Because both instruments produce low frequencies, sometimes, the both of them can get muddied up together, leaving a mix sounding too heavy and muddy on the low end of the frequency spectrum. This technique allows for the bass to duck down in volume ever so slightly whenever the kick drum is played so that the two aren’t clashing and competing with each other.
Here is an example of a kick drum and two lots of bass played at the same time. You can hear that the kick is not really relevant and that the bass takes over compared to all other elements.
With a little bit of side-chaining, this is fixable. First, we set up our compressor on both bass tracks, from here, I adjust the threshold and ratio to enable the kick to pass through and compress the bass-line whenever it hits.
The end result sounds like this:
I hope this taught you a little bit about side-chaining and compression in general! It is a really useful tool in mixing and can improve the sound and quality of mixes tenfold if done correctly!
Colletti, J. (2013). Retrieved from https://sonicscoop.com/2013/06/27/beyond-the-basics-sidechain-compression/
Mayzes, R. (2018). 4 Simple Sidechain Compression Tricks for Better Mixes TODAY. Retrieved from https://www.musicianonamission.com/sidechain-compression-guide/