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ADSR — Attack, Decay, Sustain, Release

When creating artificial waveforms in a synthesizer, changes in the signal amplitude over time are controlled by an ‘envelope generator’ which typically has controls to adjust the Attack, Decay, Sustain and Release times, controlled by the pressing and subsequent release of a key on the keyboard.

A standard ADSR envelope.A standard ADSR envelope.

The Attack phase determines the time taken for the signal to grow to its maximum amplitude, triggered by the pressing of a key. The envelope then immediately enters the Decay phase during which time the signal level reduces until it reaches the Sustain level set by the user. The signal remains at this level until the key is released, at which point the Release phase is entered and the signal level reduces back to zero.

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