A noise gate is an electronic device that is used to control the volume of an audio signal. They are commonly used in the recording studio, sound reinforcement, and small portable units are also used by rock musicians to control unwanted noise from their amplification systems.

In its most simple form, a noise gate allows a 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: the gate is closed. A noise gate is used when the level of the 'signal' is above the level of the 'noise'. The threshold is set above the level of the 'noise' and so when there is no 'signal' the gate is closed. A noise gate does not remove noise from the signal. When the gate is open both the signal and the noise will pass through.

More advanced forms of noise gates have more features. Most common is the ability to control how quickly the gate will close once the level has dropped below the threshold. This is known as the release, and allows for a smooth decay rather than and abrupt cutting of the sound when the gate closes. Likewise the ability to set the time it takes for the gate to open is available on some gates. This is known as the attack control. If the attack time is too short a click can be heard when the gate opens.

The amount of attenuation when the gate is closed can be set by the range control. Often there will be complete attenuation, that is no signal will pass when the gate is closed. In some circumstances complete attenuation is not disired and the range can be changed.

Advanced gates have a sidechain. This an additional input that allows the gate to be triggered by another audio signal.

Noise gates often implement hysteresis, that is, they have two thresholds. One to open the gate and another, set a few dB below, to close the gate. This means that once a signal has dropped below the close threshold, it has to rise to the open threshold for the gate to open, so that a signal that crosses over the close threshold regularly does not open the gate and cause chattering.

A good example of time-controlled noise gating is the well-known 'gated reverb' effect heard on the drums on the Phil Collins hit single "In The Air Tonight", created by engineer-producer Hugh Padgham, in which the powerful reverberation added to the drums is cut off by the noise gate after a few milliseconds, rather than being allowed to decay naturally.

Noise gates can also be set to activate in response to an external audio or electronic trigger, such as another sound. A good example of this use of the device can be found on the Godley & Creme concept album Consequences.

The album's story required the creation of a number of special sound effects that would convey the impression of natural disasters. For the "Fire" sequence, Godley and Creme used a noise gate, triggered by the sound of multitracked voices, that created the 'voice' of a raging bushfire.

During the recording of this segment, each time the voice signal began, it triggered the noise gate to open up another channel, which carried a pre-recorded loop of a crackling sound (created by overdubbing the sound of bubble wrap being popped in front of a microphone). The combined voices and crackling created an eerie and quite convincing 'talking fire' effect.