Envelope Generator (EG)
Just like a VCO (oscillator) , VCF (filter) and VCA (amplifier) , an EG (Envelope Generator) is very important to the signal flow of a synthesizer or modular system.
A typical envelope generator produces a signal which, as seen on an oscilloscope, appears as a series of line or curve segments.
It generates a voltage envelope in response triggered by a gate signal from a keyboard, oscillator or other source. The envelope voltage is used to control amplifiers, filters, oscillators and other components of sound.
The commonly found Attack Time, Decay Time, Sustain Level and Release Time (ADSR) is one type of envelope generator whereas more advanced envelope generators provide more segments to control, and these functions vary based on the synthesizer or module that is utilized.