Threshold

A threshold is generally a voltage level a signal needs to cross before a module takes an action. For example, when the output of an envelope follower (a module that creates a voltage that corresponds to the current level of an audio signal) rises above a threshold level, then its gate signal will go high indicating a note has started. When the output of the envelope follower falls before a threshold (which may be the same or different than the note-on threshold), then the gate goes low, indicating the note should be finishing.