The Noise Gate is a handy way of reducing noise on an Audio Input such as a Microphone

It works by quickly fading out the audio when it drops below a certain dB (decibel) Threshold

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 (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 '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.