Sidechain Compression
Last Edited: Dec 25, 2023
What Is Sidechain Compression?
Sidechain compression, also known as ducking, is an audio effect commonly used in radio and pop music, especially dance music. In sidechain compression, the presence of one audio signal reduces the level of another. In radio, this can typically be achieved by lowering (ducking) the volume of a secondary audio track when the primary track starts and lifting the volume again when the primary track is finished.
Voice-over
A typical use of this effect in a daily radio production routine is for creating a voice-over. A professional speaker reads the translation dubbs and ducks the original sound of the foreign language. Ducking becomes active as soon as the translation starts. In music, producers apply the ducking effect in more sophisticated ways where another signal's presence delicately lowers a signal's volume. Ducking here works through the use of a "side chain" gate. In other words, one track is made quieter (the ducked track) whenever another (the ducking track) gets louder. This may be done with a gate with its ducking function engaged or by a dedicated ducker.
Kick Drum Trigger
Sidechain compression is a very general term. However, it has come to be associated with a very specific type of usage. Suppose you feed a regular 4/4 kick drum into the sidechain input of a compressor and use a reasonably high ratio and low threshold along with a fast attack and a medium-to-long release. In that case, the sound will duck when the kick drum is present because the kick drum will trigger the compressor to reduce levels every time it sounds. The combined effect makes whatever you compress sound like it is pumping or sucking. If you apply this compression to the whole track, the product can be pretty intense.
Achieve Loudness
You can use this effect to take advantage of one natural phenomenon. It gives the impression that the track is louder than it is. The human ear, like any kind of listening device or recorder, limits how loud the sound can be before it distorts and overloads. When you reach these limits, your ears just compress (or limit) any sound louder than their inbuilt threshold. In the case of kick-drum-heavy club music, the kick drum will most likely trigger our ear's built-in limiter with its huge bass energy levels. When the kick drum's sound dies away, everything else will get louder for a second until the kick drum comes again. And this is exactly the effect we have been describing with sidechain compression. So, if we set the sidechain compression up correctly and on the whole mix, it can have the same effect on the sound as listening to it extremely loudly would.
Make a Bigger Mix
Our ears hear the effect and naturally make a connection between the "overly loud" effect and the "sidechain compression" effect. It gives the impression that we are listening to the track loud but at the same time quietly. Of course, nothing will ever give the same impression as listening on a huge club PA system would. However, it is a valuable side-effect of the sidechain compression process that can work in our favor to help make our mixes sound somewhat bigger.
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