Having the right plugins or hardware is brilliant, but knowing how to exploit your equipment to its extents is the goal I strive to achieve each day in my professional capacity. So here for you is another recording 101 article - Side-Chain compression.
The term 'side-chaining', also referred to parallel routing compression, simply means the splitting of an original signal and routing one of the parent signals through a alternative audio path. An example of this is splitting a guitar signal to send to a reverb unit, and then mixing the ‘wet’ reverb signal back with the ‘dry’ to end up with a either a hybrid signal output, or a 100% fully automated levelling for a group of instruments sent down a bus. Today, however, we will be discussing the art of side-chain compression for an instrument bus.
Compression doesn’t just have to be a 'corrective' tool or a hard levelling medium, it can be used musically to shape your audio with varying outcomes. Essentially side-chain compression is an extremely powerful and creative way of manipulating audio, from both a compositional and technical angle that is often not known to the novice record producer.
As a mixing method, it can be used to allow the layering of multiple audio sources, that occur in similar frequency spectrums without frequency masking. The pumping lead lines found in various electronic music genres is a very obvious use of side chain compression, where signals move out of the way of each other for musical effect. In many professional mixes the producer will use the kick drum audio channel to trigger heavier compression of the bass line groove so that pump from the bass hits hard and doesn't get lost in the complex reproduction of the frequency range and has it's own place.
So how does it work? As I have said previous, you need two signals and two compressors. For example, I am using a kick drum line to side chain to the lead bass synth in a 'House' track and will be using stock compressors that feature side-chain capabilities that most Pro Tools, Logic, Cubase etc all have.
The kick drum signal is the side-chain 'trigger' and it needs to have it's own compressor on its audio track to better define the overall dynamics. The purpose of this is so that it is appropriate for sending a good strong strong signal via a 'send'. Once you have compressed the original signal to your taste then you will need to route the signal via a send to a bus or auxiliary track that also contains a compressor. Once you have done this you and have appropriately labelled the send you will notice that the kick audio track signal will be there and will also show up on the send or aux channel. From this point, on the compressor that you have put on the bus or aux track you will need to alter the threshold, ratio and gating until you get the bass line clearly defined and that, as soon as the kick hits in, makes the bass line recede for enough time that the kick is defined but not too slow or fast. It is likely that on harder, more superior gated kicks, you will need to find exactly the right amount of time with the gating and this can take some time. When you feel like you are getting the right effect then you should play the entire track with all the other instruments in it alter the kick and bus channel levels until you reach the performance that you desire. Side-chaining is a difficult thing if you are new to it, but it is one that is worth experimenting with.
Side-chaining effectively creates a pumping and bouncy lead line that is so iconic of electronica productions and, by no means, is the only use of Side Chain compression, but is the simplest to explain the concept of it. Feel free to experiment with routing various instruments around the place to suit a number of differing applications.
Edd Harris & Chris Pavey