How To Sidechain The Sidechain

The signal a compressor listens to is called the sidechain signal. Processing a compressor’s external sidechain input can provide a huge range of ways to tweak behaviour. Here are a few suggestions…

01. Go beyond De-essing

Wanna turn a compressor into a de-esser? Boost sibilant frequencies (8kHz-ish) in the sidechain only, so the compressor responds mostly to those frequencies. On a similar note, create a ‘de-harsher’ by tuning the sidechain EQ lower, between about 2-5kHz. This can work especially well on sources like trumpets or female vocals – this tames strident high notes without dulling the overall tone, as an EQ cut in that region probably would.

02. Low-passed SideChaining

High-pass filters for the sidechain are pretty standard, and are often built into the compressor’s signal path. These are great when you want to prevent the compressor from overreacting to low-frequency content. But what if you use a low-pass filter instead? This makes the compressor disregard higher frequencies – the click of a kick drum or the snap of a snare, for example – which can result in a ‘clickier’ or snappier compression style. Some compressors or channel strip plugins (such as FabFilter Pro-C 2) will allow you to set this up internally. Otherwise, you’ll need to route a filtered signal to the compressor’s sidechain input to trigger gain reduction.

03. Unboxing Compression

Now, let’s tune the sidechain EQ lower and boost low-mids or bass frequencies. This can be a great way to reduce boxiness, muddiness or boominess without losing the fatness or fullness of tone, or weight and depth. A fairly wide and gentle boost can work well in this case, when combined with a fairly gentle compression ratio of around 2:1 to ride the overall dynamics. But, as always, you should tailor your settings to the problem in hand: if you need a sharp sidechain boost and a high compression ratio to take firm control of specific events, don’t be afraid to do so.

04. Double Compress