(1) The time it takes for a sound to reach minimum loudness; the end of a sound.

(2) The second of the four segments of a typical ADSR envelope. The decay control determines the amount of time it takes for the envelope to fall from the peak reached at the end of the attack segment to the sustain level. If no additional energy is put into the sound source (e.g., a cymbal), then the decay is the time during which the sound falls from the loudest point back to silence.

(3) The time taken for reverberation to die away. See decay time, reverberation time,RT-60.