Noise Gate
The audio noise gate allows you to attenuate audio levels that are below a set threshold. These are often used to reduce background noise from the audio output signal. The noise gate does not remove the noise, but attenuates the entire signal when it is below the set threshold. When the input audio level is below the threshold the noise gate is closed and the attenuation is applied. When the input audio level passes above the threshold, the gate opens and the attenuation is removed. You can adjust how quickly the attenuation is removed once the threshold is surpassed as well as how quickly it is applied when the audio level drops below the threshold.
Note: The noise gate is the first audio processing that is applied to the signal.