A noise gate or gate is an electronic device or software that is used to control the volume of an audio signal. Comparable to a compressor, which attenuates signals above a threshold, such as loud attacks from the start of musical notes, noise gates attenuate signals that register below the threshold. However, noise gates attenuate signals by a fixed amount, known as the range. In its simplest form, a noise gate allows a main signal to pass through only when it is above a set threshold: the gate is 'open'. If the signal falls below the threshold, no signal is allowed to pass (or the signal is substantially attenuated): the gate is 'closed'. A noise gate is used when the level of the 'signal' is above the level of the unwanted 'noise'. The threshold is set above the level of the 'noise' and so when there is no main 'signal', the gate is closed.
A common application is with electric guitar to remove hum and hiss noise caused by distortion effects units. A noise gate does not remove noise from the signal itself. When the gate is open, both the signal and the noise will pass through. Even though the signal and the unwanted noise are both present in open gate status, the noise is not as noticeable. The noise becomes most noticeable during periods where the main signal is not present, such as a bar of rest in a guitar solo. Gates typically feature 'attack', 'release', and 'hold' settings and may feature a 'look-ahead' function.