Everyone talks about the compressor, rarely about its mirror image. Yet the noise gate and the expander fix a problem the compressor never touches: the bottom of the signal, the silence, the hiss, the spill. Used well, they clean a mix without being heard; set badly, they chop note tails and smother the life out of a take. Here is how they work, and how to actually use them.
What a gate is for
A compressor acts on what’s too loud. A gate and an expander act on what’s too quiet. The principle: below a certain level, the signal is attenuated, or cut entirely. The result is that you silence what shouldn’t be heard between the notes — amp hiss, the air conditioning under a vocal, the snare bleeding into the hi-hat mic, a singer’s breath between phrases. A gate doesn’t “remove” noise as such: it masks it when the useful signal stops, exactly where the ear would notice it most.
The parameters that matter
A gate runs on a handful of controls, each with an audible consequence:
- Threshold: the level below which attenuation kicks in. Too high and you clip note starts and ends; too low and the gate does nothing.
- Range (or depth): how much you attenuate below the threshold. A “soft” gate pulling 10-15 dB often sounds more natural than a full cut, which leaves abrupt holes.
- Attack: the opening speed. On a percussive source (snare, kick), too slow an attack eats the transient; on a vocal, too fast an attack clicks.
- Hold: the minimum time the gate stays open after triggering. It prevents chattering, that nasty flutter when the signal hovers around the threshold.
- Release: the closing speed. Too short and note tails are truncated and artificial; too long and the noise returns before the cut.
- Hysteresis: a closing threshold set lower than the opening threshold. This is the trick that stabilises a gate: it opens at one level and only closes at a lower one, killing parasitic oscillation.
Gate or expander: the real difference
The gate is a brutal version of the expander. An expander gradually increases attenuation as the signal drops below the threshold, following a ratio (1:2, 1:4…), exactly like a compressor in reverse. A gate applies a fixed attenuation once the threshold is crossed. In practice, the downward expander is almost always the musical choice: it reduces the noise floor without murdering reverb tails or nuance. Save the hard gate for percussive sources and cases where you genuinely need silence. The compressor works the top of the dynamic range; the expander, the bottom. Understanding one helps you set the other — our guides to setting a compressor lay the groundwork.
Detection: sidechain and the key filter
Like the compressor, a gate triggers from a detection signal you can filter. That’s the key to clean settings: on a tom, a band-pass filter centred on the drum’s fundamental stops the snare from opening the gate by accident. You can also trigger a gate from another track — that’s the whole idea behind sidechaining, used for instance to tighten a kick against a sub-bass. A good detection setting often solves what a badly placed threshold can’t.
Real-world uses
A few situations where the gate and expander save a take:
- Drums. Gating toms and snare to contain spill and tighten the hit. This is the gate’s historic home turf, to the point that some plugins, such as the Sonnox Oxford Drum Gate, analyse the hit to open at the right moment.
- Vocals. A gentle expander removes preamp hiss and room between phrases, without cutting the breaths that give a performance life.
- Guitar amps. A gate tames the hiss of a high-gain amp between riffs — one of the most common uses on stage and in the studio.
- Noise-floor cleanup. On a take polluted by air conditioning or a hum, the expander lowers the floor when the useful signal falls silent.
Pitfalls to avoid
The gate is the tool you hear most when it’s set badly. Three mistakes recur: too short a release that truncates note tails and sounds “electronic”; a threshold set blind without listening to the quietest passages, which ends up cutting nuance; and no hysteresis, which lets the gate flutter around the threshold. The rule is simple: always set a gate on the quietest passages of the track, never the loudest. And think transients — to sculpt the attack without touching dynamics, a transient shaper is sometimes more accurate than a gate. For the broader family, see our take on dynamic EQ and de-essing.
My take
The gate has a bad reputation, and it’s earned: too many tracks get wrecked by a cut that’s too sharp. The gentle expander is almost always the right reflex, because it fixes the fault without drawing attention to itself — which is exactly what you want from a cleanup tool. The real luxury of digital here is the smart-detection gate with look-ahead, opening right on the transient without clipping it. One tip that applies to everything else: if you can hear the gate working, it’s set wrong. Back off the threshold, lengthen the release, and let the take breathe.
