Gate and expander

What it is and how it works

Gates and expanders are the opposite of a compressor: they act below the threshold. When the signal falls below the threshold, they turn it down.

• Gate: turns down everything below the threshold by a lot (or all the way to silence). It is a switch with opening and closing times.
• Expander (downward): turns it down proportionally, with a ratio (1:2, 1:4): 1 dB below the threshold becomes 2 or 4 dB below. Softer and more natural.

Uses: removing background noise, amp hum, bleed (other instruments leaking into the microphones), room sound, breaths; shortening tails (kick, toms, snare); rhythmic effects (trance gate, gated reverb).

Parameters one by one

• Threshold: opening level. Set it just above the noise or bleed and below the softest hit you want to keep.
• Range / Floor / Depth: how far it turns down when closed. −∞ = silence; −10/−20 dB sounds much more natural (a bit of room stays). In Fruity Limiter (Noise Gate) the GAIN control sets the level when the gate is closed (default 100% = no gating).
• Ratio (expander): 1:1.5–1:2 for light noise reduction; 1:4 and above approaches a gate.
• Attack: opening speed. 0.01–1 ms for drums (don't lose the transient); 1–5 ms for vocals and guitars (avoids clicks).
• Hold: minimum time it stays open after the signal drops: 10–100 ms. Prevents "chattering" (rapid open-close).
• Release / Decay: closing speed. Short (20–80 ms) = dry, cut-off sound; long (150–500 ms) = natural tail. On toms and snare, tie it to the tempo.
• Hysteresis: difference between the opening and closing thresholds (2–6 dB), prevents repeated openings.
• Key / sidechain filter: the detector listens to a filtered version: on a snare mic, put an HP at 150–200 Hz and an LP at 5–8 kHz in the key so the gate isn't opened by the kick and cymbals.
• External sidechain (key input): the gate opens from another signal (kick opening a sine sub, hi-hat opening a pad).
• Lookahead: 1–5 ms so the attack isn't cut off.
• Flip / duck: inverts the logic (it turns down when the signal exceeds the threshold).

Tools

• FL Studio: Fruity Limiter Noise Gate tab (GAIN, THRESH, REL); Effector TRANS (tempo-synced rhythmic gate, Release and Drop level); Gross Beat (volume patterns, trance gate); LuxeVerb Envelope (positive scale = gated reverb); Transmitter (separates transient and sustain: you can turn the sustain down like a transparent gate). Edison for manual cutting.
• Third party: FabFilter Pro-G (gate/expander/ducker with sidechain), Waves C1 Gate, Kilohearts Gate, ReaGate (ReaPlugs, free), Drumgate (Klevgrand/Accusonus) and trigger tools such as Slate Trigger.

When to use it and on what

• Toms: the classic case; gate with key filter and tempo-matched release to eliminate cymbal noise between hits.
• Miked snare and kick: reducing cymbal bleed (range −10/−15 dB, not −∞).
• High-gain distorted guitars: eliminating hiss and hum between riffs (metal: gate before the amp sim and/or after). Threshold just above the hiss, fast attack, release 50–150 ms for staccato riffs.
• Vocals: light expander (1:2, range −6/−10 dB) to turn down breaths and room between phrases; better than a gate.
• Drum samples with long tails: shortening the kick or the 808 (today the sampler envelope is often used).
• Effects: gated reverb (see "Reverb: types"), trance gate on pads, "stutter".

Starting settings

By genre

• Metal: gate is essential on high-gain guitars and bass and on acoustic drums.
• Rock and pop with real drums: gate or expander on toms, rarely on anything else (hand editing is preferred).
• Electronic: gate as a rhythmic effect (trance gate) and for gated reverb on snares.
• Hip hop: rarely needed (clean samples); expander on vocals recorded in noisy rooms.

Common mistakes

• Range −∞ on everything: unnatural sound, "holes" of silence between hits.
• Attack too slow: the transient is lost (kick and snare without punch).
• Release too short: truncated tails, clicks.
• Gate on vocals with a high threshold: you cut weak consonants and the ends of words.
• No key filter: the kick opens the snare's gate.

How to hear it

• Listen to the silence between hits: the noise should drop without the hit changing.
• Watch the opening indicator: it should open on every intended hit and never on the bleed.
• Compare range −∞ and −15 dB: the second usually sounds more "in the room".