|ADSR is a simple reduction of what is generally a more
complex dynamic envelope. In synthesizers or samplers it may be used
to control amplitude, filter cut-off, or tuning (to name a few likely parameters).
In older analogue synthesizers, the ADSR created a transient control voltage
which was used in conjunction with a voltage controlled amplifier, filter
or oscillator. It required a trigger
to turn it on. In more contemporary models it often refers to both
the envelope and the process. In most applications the
attack, decay and release segments have preset durations while the sustain
segment gets its duration from the trigger. This is based on the
model of an organ which will sustain as long as the key is depressed.