The parameters for this are the same as normal compression, with threshold and ratio dictating how severe the gain reduction is. This pulls down the bass line volume when the bass drum plays, which enables you to have consistent bass energy without the usual volume bump as two bass-orientated sounds play at the same time. Classic uses of this setup include compressing a bass line when a bass drum plays by feeding the compressor that processes the bass line with a copy of the bass drum as its key input. This enables you to feed any external audio signal you want to the key input, so that it’s a different signal controlling the amount of gain reduction from the signal present at the processing input. It’s external sidechaining that is responsible for the popular effect heard on so many records today.

This section is called the sidechain, which is technically correct – but it’s an internal sidechain, not an external one. This lets you choose which rhythmic element makes the compression kick in, or pump, rather than reacting to all elements present in the signal. For instance: by filtering the key signal with a low-pass, you can focus on just the bass drum of a busy drum mix, which in turn will eliminate gain reduction being triggered from other sounds in the signal (like the snare drum, for example). This is designed to make the gain detection react to the dynamics of specific frequency areas of an audio signal. This section listens to the key signal, then applies gain reduction to the main signal passing from the input to the output.Ī common point of confusion is the inclusion of filters for this internal sidechain section on some plug-ins. The other copy is sent as the internal sidechain – or key input – which goes into the gain detection section. One copy passes through to the output with the desired gain reduction applied to it. When using a sidechained compressor, the signal you want to process at the input section is split into two.

Fruity peak controller sidechain