Timbre and envelope are two characteristics of sound waves that help determine why, say, two instruments can play the same chords but sound nothing alike.
Timbre is determined by the unique harmonics formed by the combination of notes in a chord. The A in an A chord is only its fundamental note—you also have overtones and undertones. The way these sound together helps keep a piano from sounding like a guitar
envelopes, which determine how a sound’s amplitude changes over time
Envelopes comprise four parts: Attack, Decay, Sustain, and Release
Attack: This is how quickly the sound achieves its maximum volume. A barking dog has a very short attack; a rising orchestra has a slower one.
Decay: This describes how fast the sound settles into its sustained volume. When a guitar player plucks a string, the note starts off loudly but quickly settles into something quieter before fading out completely. The time it takes to hit that sustained volume is decay
Sustain: Sustain isn’t a measure of time; it’s a measure of amplitude, or volume. It’s how loud the plucked guitar note is after the initial attack but before it fades out
Release: This is the time it takes for the note to drift off to silence.
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