Definition
Decay — The time it takes for a sound to fall from its peak attack level down to the sustain level, representing the second stage of an ADSR envelope.
Decay Explained
After the attack phase pushes a sound to its peak volume, decay is what happens next. The sound drops from that peak to a lower, steady-state level called the sustain. How quickly this drop happens depends on the decay time setting. A short decay of 10 milliseconds means the sound falls to sustain almost instantly after reaching peak. A long decay of 2 seconds means a gradual, audible fade from the peak down to the held level.
Decay is the parameter that separates percussive sounds from sustained ones. A piano note has a clear decay: the hammer strikes the string at full force (attack), and the volume immediately begins dropping (decay) to a lower level that sustains while the key is held. A pipe organ has almost no decay: the sound reaches full volume during attack and stays there as long as the key is pressed, with the sustain level equal to the peak.
In the context of filters, decay works differently than volume decay. A filter envelope with fast decay opens the filter cutoff briefly during the attack phase, then closes it quickly back to the sustain position. This creates the plucky, snappy tone heard in bass synthesizers where brightness appears for a split second then disappears, leaving a darker sustained tone.
How Producers Use It
Drum sound design revolves around decay time. The difference between a tight, controlled kick drum and a booming, room-filling one is almost entirely a matter of decay length. Producers adjust the decay of sampled and synthesized drums to match the tempo and style of their beat. At faster tempos, shorter decays prevent drum hits from overlapping. At slower tempos, longer decays fill the space between hits.
For synthesized bass sounds, the filter decay is the most important parameter. A medium filter decay (100-300 ms) creates the classic pluck bass: bright on the initial attack, quickly darkening as the filter closes. Shorter filter decay makes the bass more percussive. Longer filter decay produces a wah-like sweep that adds expressiveness to bass lines.
The 808 is the ultimate example of decay in action. The entire character of an 808 bass depends on its amplitude decay, which determines how long the sub-bass sustains after the initial hit. Producers tune this decay to match the rhythmic spacing of their pattern, ensuring notes sustain long enough to carry the low end but do not overlap into the next hit unless an intentional legato effect is desired.
Battle Tip: Match your drum decay to your BPM. At 140 BPM, a kick with a 500 ms decay will muddy the groove because hits land too close together. Shorten the decay to 200 ms for punch and clarity. This simple adjustment can transform a mushy drum pattern into a tight, competitive groove that judges feel in their chest.