An envelope generator is a module that creates a time-varying control voltage signal, following a predetermined shape defined by its stages. This control voltage, often referred to as an “envelope,” is used to modulate various parameters of a synthesizer, such as amplitude, filter cutoff frequency, or modulation depth. Envelope generators are essential in shaping the dynamic and expressive characteristics of synthesized sounds.
There are several types of envelope generators, with the most common being the ADSR (Attack, Decay, Sustain, Release) envelope. Other types include AD (Attack, Decay), AR (Attack, Release), and more complex forms like DADSR (Delay, Attack, Decay, Sustain, Release) and AHDSR (Attack, Hold, Decay, Sustain, Release).
An envelope generator typically has inputs for triggering the envelope, such as a gate input, and outputs for the generated envelope signal. In a modular synthesizer, you can patch the output of an envelope generator into the control voltage input of other modules, such as a VCA (Voltage Controlled Amplifier) for controlling amplitude, a VCF (Voltage Controlled Filter) for modulating the filter cutoff, or any other voltage-controlled parameter within the system.
By adjusting the stages of the envelope generator, users can create a wide variety of dynamic and expressive synthesized sounds, ranging from short percussive hits to evolving pads and everything in between. The flexibility of modular synthesizers allows for extensive experimentation with envelope shapes and modulation destinations.