Sound & signal
Attack and release
Attack sets how quickly a compressor responds once the signal crosses the threshold; release sets how quickly it stops once the signal falls back. Together they decide whether you hear the processor or the music.
In practice
Fast attack kills punch, slow attack keeps it. Release in time with the beat grooves; release out of time breathes.
Start slow on attack — let the transient through and compress the body behind it — and set release by ear against the tempo until the recovery disappears into the groove rather than fighting it. Auto-release is a reasonable default on anything with a varying tempo. And note that this is exactly the mechanism behind sidechain ducking: the same two controls, deliberately set so you hear the pump.
Slow
Attack, to keep punch
In time
Release, to keep groove
Both
What ducking exaggerates
Where these come from: Standard dynamics practice, not catalog figures. For what we can measure, see the deliberate version.
Why it matters
They are why two compressors set to identical threshold and ratio can sound completely different. A fast attack catches the front of every kick and flattens the punch; a slower one lets the transient through and clamps what follows, which is the difference between a track that hits and one that merely is loud.
Release is where pumping comes from, and pumping is either the point or the problem. Set to recover roughly in time with the beat it becomes a groove; set slightly wrong it becomes a breathing noise underneath the record that nobody can identify and everybody can hear.
Frequently asked
Why does my compressed track lose its punch?+
The attack is too fast, so it is catching the front of every kick. Slowing it lets the transient through and compresses the body behind it instead.
What causes pumping?+
A release that recovers audibly between hits. Timed against the tempo it becomes a groove; timed badly it is a breathing noise under the record.
Is sidechain the same thing?+
The same controls used on purpose. Sidechain ducking sets attack and release so the pump is the effect rather than a side effect.
Related terms
Threshold
Threshold is the level above which a compressor or limiter starts working. Below it nothing happens; above it the processor reduces gain by whatever the ratio says.
Ratio
Ratio sets how hard a compressor reduces anything above the threshold. At 4:1, four decibels of input above the threshold become one of output. At 20:1 or beyond it stops being compression and becomes limiting.
Ducking
Ducking pulls one signal down whenever another plays — almost always everything else dropping on each kick. It is the pumping motion at the heart of most house and trance.
Transient
A transient is the short burst of energy at the start of a sound — the click of a kick, the snap of a snare. It is what makes percussion readable and what beat detection listens for.
Explore: LUFS meter · Ducking · Transient · All DJ terms