Noise gate
An automatic door for audio: loud enough gets through, while hiss and room noise in the gaps get turned down or muted.
See it
What it is
A noise gate watches the signal level and closes when it falls below a threshold. Closed can mean fully muted or merely turned down by a set range. Attack controls how quickly it opens, hold keeps it open through tiny gaps, and release decides how naturally it closes after the sound ends.
Use it when the wanted sound is clearly louder than the unwanted sound: hiss between voiceover phrases, amp buzz between guitar notes, or bleed between drum hits. Set the threshold just above the noise floor, then make the release long enough to keep word endings, cymbal tails, and room decay intact. A downward expander does the gentler version by turning quiet material down instead of chopping it off. Gates also make sounds nobody could record: the huge 1980s gated drum sound, most famously on Phil Collins' In the Air Tonight, is a gate slamming shut on a reverb tail.
Gotcha: a gate cannot remove noise while someone is speaking, because the gate is open then. Push the threshold too high and it eats breaths, soft syllables, and the ends of words; use too little hold and it chatters open and shut. For constant noise under speech, reach for noise reduction before the gate.
Ask AI for it
Clean the pauses in this voice recording with the AutoGate section of Adobe Audition's Dynamics effect. Measure the noise floor, set the gate threshold about 6 dB above it, start with 5 ms attack, 100 ms hold, and 150 ms release, then adjust so every quiet syllable and breath that belongs to the performance survives. The gate must not chatter or clip word tails; use gentle downward expansion instead of a hard mute if the room tone pumps in and out.