Noise gate
A dynamics processor that shuts the signal off when it drops below a threshold — silence becomes actual silence instead of hiss and spill.
Where a compressor pushes down what is too loud, a gate chokes what is too quiet. The controls are familiar: threshold, attack, hold (how long it stays open after the signal falls) and release, plus range, which decides whether it closes completely or just dips by a few decibels. The classic job is drum mics, where the snare mic otherwise picks up the whole kit between hits, and guitar amps that hum in the pauses.
Fed from a sidechain, the gate can be triggered by a different signal. Hugh Padgham and Phil Collins gated a huge room reverb on the drums in the early 1980s and got the sound that went on to define a decade — gated reverb, an accident that became a genre.