Gate

This is one of the main signal types that are passed around inside a modular synthesizer. It jumps to high level – typically 5 volts – when a new note is supposed to start (such as when you press a key on a keyboard controller), or when a sequencer jumps to the next “stage” or note. A gate typically stays at that level for the duration of the note (i.e. while the key is being held down), and suddenly drops or “goes low” to its resting level – typically 0 volts, but sometimes –5 volts or another number – when the note ends (i.e. when the key is released).

In practice, when a gate signal is sent to a typical envelope generator, the start of the gate (when it “goes high”) tells the envelope to go through its Attack and Decay stages; while the gate remains high, the envelope stays at its Sustain level, and when the gate goes low again, the envelope moves onto its Release stage.