Sidechain Compression

One part steps back when another appears, and timing plus amount matter more than the ratio.

Related

SidechainCompressorBusDrum Kit

The problem

Sidechain is often treated as a pump switch for dance music. Its real job is to make one part step back when another appears.

Goal and judgement

Decide who triggers, who moves, and by how much. Kick triggering bass is the common pair; vocal triggering a pad also works. The move should happen for the few milliseconds needed, not for the whole bar. Too long a release drags the groove; too short a release clicks.

Method

Send the kick to the sidechain input and set the threshold so only the kick triggers. Try 2 to 1 up to 4 to 1, attack 1 to 10 ms, release around 80 to 200 ms following the tempo. Check the gain-reduction meter for 3 to 6 dB per hit. For a more natural result, use dynamic EQ or volume automation instead. Compare the full section when bypassing, not just the meter.

What to listen for

Whether the bass returns quickly after each kick; whether the pump lands on the beat; whether bypassing the sidechain makes the low end muddy; whether the chorus is over-pumped.

Common misconceptions

That sidechain belongs only to dance music; that a shorter release is tighter; that sidechain replaces arrangement.

Sources

• Giannoulis, Massberg and Reiss, Digital Dynamic Range Compressor Design, JAES 2012 — background checked, not quoted
• Bobby Owsinski, The Mixing Engineer's Handbook, sidechain section — background checked, not quoted

Used for fact-checking only; all prose is original.