Introduction
An audio effect called noise gate can be regarded as an expander with a slope of -∞. With this feature, the effect results in total muting of the signal below the chosen threshold. As already deduced from its name, the basic application of noise gate effect refers to gating out the noise by setting the threshold just above the level of the background noise. This further leads to opening of the gate only when the desired signal with the level above the threshold is present. In order to explain this more clearly, we can say that noise gate is used when the level of the “signal” is above the level of the “noise”.
Noise gate parameters
A typical noise gate effect possesses the following parameters which are in charge of controlling the effect: threshold, attack, hold, decay, and range. Additionally, there might be high and low-frequency controls as well as an external side-chain option in more advanced units.
Threshold
Is in charge of setting the level at which the gate will open.
Release
Used to define the length of time the gate takes to change from open to fully closed. It is the fade-out duration. A fast release abruptly cuts off the sound, whereas a slower release smoothly attenuates the signal from open to closed, resulting in a slow fade-out. If the release time is too short, a click can be heard when the gate re-opens. Release is the second-most common control to find within a gate, after Threshold.
Attack
Used to define the length of time the gate takes to change from closed to fully open. It is the fade-in duration.
Hold
Used to define the length of time the gate will stay fully open after the signal falls below the threshold, and before the Release period is commenced. The hold control is often set to ensure the gate does not close during short pauses between words or sentences in a speech signal.
Range
Used to set the amount of attenuation to be applied to the signal when the gate is closed. Often there will be complete attenuation. This means that no signal will pass when the gate is closed. In some circumstances, complete attenuation is not desired and the range can be changed.
External sidechain
Furthermore, there is an external sidechain option available in more advanced types of noise gate effect units. This is an additional input that allows the gate to be triggered by another audio signal. Furthermore, newer types of effects that derivate from the noise gate are “trance gate” or simply “the gate”. In these types of effects, the noise gate is not controlled by an audio signal but a preprogrammed pattern. This is resulting in precisely controlled chopping of the sustained sound.
Additional Resources & Source Texts
http://www.prosoundweb.com/channels/church/noise_gates_101_what_they_do_how_to_use_them_optimally/
