Instrument sound envelopes are described by attack, decay, sustain, and release phases

Evidence

The principal characteristics of a sound envelope are the attack, the body, the transients (or internal changes) and the decay. When the body of the sound is prolonged and unchanging, it is reproduced by the graphic level recorder as an extended horizontal line. — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 269 (#qualifies, via linked claim)

We may call the sound object the smallest self-contained particle of a soundscape. Because it possesses a beginning, middle and end, it is analyzable in terms of its envelope. Envelope is a graphic term but the ear can be trained to hear its characteristics, which are defined as attack, body (or stationary state) and decay. — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 442 (#qualifies, via linked claim)

When considering the notes played on pitched musical instruments, timbre relates to those aspects of the note which can be varied without affecting the pitch, duration or loudness of the note as a whole, such as the spectral components present and the way in which their frequencies and amplitudes vary during the sound. … The onset and offset portions of a note tend to last for a short time, of the order of a few tens of milliseconds (or a few hundredths of a second). Changes that occur during the onset and offset phases, and in par­ ticular during the onset, turn out to have a very important role in defining the timbre of a note. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1454 (#expands, via linked claim)

Categorization

• XREF: connects to: An instrument’s normal attack transient is essential to its characteristic timbre; A sound envelope is defined by attack, body, transients, and decay — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 269; A sound object is analyzable into attack, body, and decay — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 442 (+1 more)

Broader Connections

• A sound envelope is defined by attack, body, transients, and decay #qualifies (0.90) — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 269
• A sound object is analyzable into attack, body, and decay #qualifies (0.85) — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 442
• Attack and release phases lasting milliseconds largely determine a note’s timbre #expands (0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1454