An envelope follower, also known as an envelope detector or envelope extractor, is a module that analyzes an incoming audio signal and generates a control voltage (CV) signal based on the amplitude variations of the input signal. Essentially, it “follows” the contour of the input signal’s amplitude over time and creates a corresponding CV output, which can be used to modulate other parameters within the modular synthesizer.
The primary function of an envelope follower is to enable the dynamics of one signal (e.g., an audio source or another control voltage signal) to control or modulate the parameters of another module or process within the synthesizer system. Some common use cases for an envelope follower in a modular synthesizer include:
- Dynamics processing: An envelope follower can be used as a sidechain input to control the amplitude or filter of a sound, creating effects such as ducking or pumping, commonly used in electronic music production.
- Modulation source: The output of the envelope follower can be patched into the control voltage input of other modules, such as oscillators, filters, or VCAs, allowing the dynamics of the input signal to modulate their parameters, creating expressive, dynamic, and evolving sounds.
- Generating triggers or gates: An envelope follower can be combined with a comparator to generate triggers or gates based on the amplitude of the input signal, which can then be used to control other modules, such as sequencers or envelope generators.