Gate

A gate is a control signal that stays at a high voltage for a set length of time. Gates signal when an event starts and when it ends. For example, pressing a key on a keyboard sends a gate that stays high for as long as the key is held and drops low when the key is released. Gates are typically used with envelopes that have a sustain stage, such as ASR or ADSR, where the gate length sets how long the sustain lasts.