An automatic volume reduction on one signal triggered by the presence of another, most often used so a bassline or pad pulls back each time the kick drum hits.
Ducking is a dynamic effect where one audio signal is automatically reduced in volume in response to a second signal arriving at a sidechain input. In practice, a compressor monitors a trigger source (commonly the kick drum) and attenuates the target signal (commonly the bass or a pad) in near-real time each time the trigger crosses a threshold.
Why it matters
Ducking keeps the low end of a mix clean and punchy by preventing the kick and bass from competing for the same frequencies at the same moment. It also creates the rhythmic pumping sensation that defines much of house and techno, giving a track forward momentum on the dance floor.
In practice
When applying ducking via a sidechain compressor, set a fast attack (1-5 ms) to catch the kick transient immediately and a release (50-150 ms) timed to the track's BPM so the bass returns to full volume before the next beat. A release that is too slow kills the groove; too fast causes an audible snap.
