Sidechain Compression
A compression technique where one signal triggers the compressor on another — most famously, kick drum ducking the bass to create separation.
Normal compression listens to and reduces the same signal: the kick drum compressor watches the kick and turns it down when it gets loud. Sidechain compression breaks that link. The compressor sits on signal A (say, the bass), but it listens to signal B (the kick) for the trigger. Every time the kick hits, the bass ducks. The two never fight for the same space, and the mix feels punchier without either being quieter.
In dance music, sidechaining is a sound in itself. A pad or bassline gets aggressively pumped down on every kick, creating the breathing, rhythmic motion that defines house, trance, and EDM. In rock and pop, sidechaining is usually subtler — 2–3 dB of duck on the bass when the kick lands, enough that the low end stays defined but you barely notice the gain reduction happening.
Beyond kick/bass, sidechaining solves competing-frequency problems anywhere. A bus compressor sidechained to the vocal can pull the whole mix down a hair on each phrase, making the lead vocal sit forward without raising its fader. Lead synths sidechained to the snare give a track a clearer backbeat. The principle is always the same: one source triggers, another responds.