800px-ADSR parameter.svg

Schematic of the ADSR envelope controlling amplitude.

The ADSR Envelope is component of syntheizers used to various parameters including volume, filter cutoff etc. The letters in 'ADSR' stand for Attack, Decay, Sustain, and Release respectively.

Attack: Attack is the time the parameter takes to reach its peak after being triggered.

Decay: Decay is the time the parameter takes to reach its sustain level.

Sustain: Sustain is the time for which the parameter stays constant after decaying but before the release.

Release: Release is the time the parameter takes to drop off to nil again.

There are two types of slopes that the attack, decay and release times will observe; linear and exponential. These different slopes can be attributed to hardware envelope generators and their capacitor charging methods. A voltage source charging the capacitors of a hardware envelope generator will result in an exponential slope, while a constant current source will result in a linear slope. Both methods have their merit, and software envelopes will observe either depending on the creators intent.