In this article, Headliner takes a look at the sometimes confusing world of sidechain processing and attempts to give you an overview of, as well as some of the more common uses for this incredibly useful technique.
What is Sidechain Processing in Music Production?
In pure layman’s terms: ‘Sidechain processing is the manipulation of one audio track by means of another.’
Let’s refer to the audio track we want to process as the ‘Original’ audio, and the second track we use to process the original audio as the sidechain. You may also have come across the terms ‘Key’ or ‘Trigger’ - these also refer to the sidechain audio track. What’s useful to know is that the sidechain could be a copy of the original audio that has been manipulated in some way, or a completely different audio track altogether.
However, to fully appreciate the concept of sidechain processing, it’s necessary to delve into a little bit of studio history and scrutinise a couple of iconic vintage analogue audio devices.
Drawmer DS201 Dual Noise Gate
In the early ‘80s, the Drawmer DS201 rack unit became the ‘industry standard’ throughout the world. Whether for studio or live, it became the go-to gate for drum isolation as well as noise reduction, ducking and other sound design duties. The unit offered a Key (sidechain) source selection switch from either the Internal Audio (Original) or a separate ‘Key Input’ external audio source via a balanced jack input. While this was not a new feature, the ability to apply high and low pass filtering to the sidechain audio path from the DS201’s front panel was.
How does this improve the function and accuracy of the noise gate, you may ask. Say for example you’re recording a jazz drummer and there’s a lot of intricate ghost strikes to the snare, as well as busy and often quite loud hi-hat work. To avoid crosstalk that is relatively high in level, as well as spurious triggering of the gate by unwanted components in respective microphones, this is done by selecting Key Source and using the high-pass filter on the Hi-Hat channel to remove low end audio information produced by the snare and likewise, the low-pass filter on the snare channel to reduce the high end audio information from the hi-hats.