ADSR and Envelope Filters
ADSR stands for Attack, Decay, Sustain, and Release, the common aspects of an envelope filter. These 4 terms refer to stages of a note's lifecycle. They are popular in synthesizers, where they can control the synth's volume, a cutoff frequency, resonance, or other signal-altering effects. However, many natural instrument sounds, such as picking a guitar string, banging a drum, or hammering a vibraphone all have a signature ADSR pattern. Other instruments allow more control over dynamics, such as the trumpet, violin, and human voice. This is most obvious in terms of dynamics, but can also be applied to formants, vibrato, and other modulations.
- Attack - The time it takes before the signal reaches peak strength
- Decay - The time it takes for the signal to fall from peak strength to sustain strength
- Sustain - The level at which the signal sustains relative to its peak strength
- Release - The time it takes for the signal to fall to 0 from its sustain level when the signal is no longer triggered
The term envelope filter comes from the lines made from a graphical representation of the ADSR settings - it tends to look like the back of an envelope, with its folded tab, similar to an uppercase 'M'.