Synth’s are made up of several building block components, one of which is the Voltage Controlled Amplifier (VCA) or amp envelope for short. This post explains the amp envelope and demonstrates some common envelope configurations with diagrams and audio examples.


The VCA

The VCA is always attached to a modulator called an ‘envelope’. The job of the envelope is to control how the volume of the amplifier changes over time. Unlike a compressor which reacts to the incoming signal envelope, the envelope designs the shape using four parameters.

A    Attack TimeThe time is takes to reach full value.
D    Decay TimeThe time is take from full value to sustain level.
S    Sustain LevelThe level the note holds while being played.
R    Release TimeThe times it takes for the note to go from the sustain level to zero once the key is released.

 

 

Common Amp Envelope Configurations

TypeADSRMusical ExampleDiagram
SwitchAttack: 0Decay: 0Sustain:100%

Release: 0

Organ
PercussiveAttack: 0 Decay: 10-80%Sustain: 0

Release: Same as decay

Drum hits
Damped PercussiveAttack: 0Decay: 10-80%Sustain: 0

Release: 0

Piano
SustainingAttack: 0-10%Decay: 0-10%Sustain: 50 – 90%

Release: 0-10%

Blown or bowed instruments (e.g. flute or violin)
QuirkAttack: 0%Decay: 10-30%Sustain: 0%

Release: 50 – 100%

Creating random, atmospheric type sounds.

Final Word

The amp envelope is important because it gives us a way to visualize and manipulate sounds. It’s not something reserved exclusively for synthesizers and electronic music, it is vital for every producer/engineer whether they work with electronic, gangsta rap, ragtime, rock or even bluegrass!