What Is A Side Chain?

Last month I showed you how I make drama loops using a vocoder. Keeping it in the box we had to utilise a thing called a side chain to get a ‘carrier’ signal into the vocoder synth. On researching “side chain” the internet gave me very little. The specifics of what you can do with a side chain yes, but what an ACTUAL side is? Nada. So here’s a brief article that I hope will define what a Side Chain is and then illustrate what you can do with it.

The side chain signal acts as a reference to the modulator and therefore links the two signals. Hence the use of the word “chain”. If you look at the shot of the Neve above, the side chain button is an arrow, depicting that the signal sits to the side of the signal to be modulated purely as a means of informing the modulator what to do.

Side Chain Compression

As mentioned above, a dynamic modulator or compressor is set to suppress a signal by a certain amount, according to its settings when certain criteria are met, again according to its settings. By inserting a side chain, this governs how the compressor affects the raw signal in keeping with these criteria. An excellent use of side chain compression is ducking. So when a side chain signal comes in, the original ‘raw’ signal gets out of the way a little bit. Great, say, for use on the radio. The music is slamming away through the compressor and isn’t bothered, the announcer speaks, and her microphone is bussed into the side chain, and the music obediently gets out of the way. When she stops speaking, the music doesn’t slam back in because the compressor’s release is set to a slow time, so over a second or so, the music gently glides back in. Where music is concerned, side chain compression can work on the same principle of moving stuff out of the way. Great if you really want the kick drum to take precedence for the short moments of time that it is playing. Another approach is to wrap instruments around each other. In this first of three quick tips, I show how I create cool ‘pumping’ synth parts with the help of a Chili Pepper and a side chain.

Side Chain Gating

This really is the original home of the gate, and I love doing this on the computer because it suddenly turns your DAW into a modular synth. Whilst gating stages are common on many synths, they’re not so on orchestral plugins, but by whipping out a side chain you can rhythmically gate material that wouldn’t usually be treated this way! So in this case, the signal goes into the dynamic modulator or gate and its criteria are set so that this gate doesn’t open until the side chain signal has reached -6db. The signal itself may be banging the gate down at -9db, but the gate is obstinate and doesn’t open. This is because it is being governed by the side chain. The minute a signal passes into this that is above -6db, the gate opens. But not necessarily immediately - if the ‘attack’ time is slow, the gate will gently open. Will it slam shut once the signal in the side chain goes below -6db? Yes, if the hold and release are short. But if the hold is long, it will wait a little bit, and then close as quickly as is governed by the release setting. With gating, all of this is really important to keep something clean and musical, as opposed to stuttery and confused.

Side Chain Ducking

This is a dying craft, and indeed the function isn’t available on a lot of plugins. But you can reverse a gate so that it closes once a signal meets its setting’s criteria. So, taking the example above, music is slamming through the main signal at -3db and the gate is set to a threshold of -6db on the side chain, but the gate is open even though there is no signal in the side chain? Well, that’s because it is set to duck. Signal comes in at -5db and smacks the gate shut according to its settings. I first became aware of this when recording kits. You’d often put two mics on a snare drum, one over the top near the rim, and one underneath near the actual snare trap. This is so you can capture those all important and very funky ghost notes. But when the drummer smacks the drum on the main 2 and 4 beats, you don’t want a fuzzy snare sound, you want the crack of the rim. By ducking the bottom mic against the top mic, you get a tight sound with all the bounce and funk of the ghosts.

In this video, I demonstrate how to overcome ducking with a gate plugin that doesn’t have this function, and more importantly, demonstrate how you can use a side chain to protect your family from nuclear attack:

Other Uses Of Side Chain: