Noise Gate

Noise gates are usually used in the following situations:

1. Reduce background noise in a recording, such as the hum of an air conditioning unit
2. Help eliminate leakage between instruments in a live recording environment

There is no benefit in gating sampled drums and instruments, as there is usually no noise or leakage between other instruments present.

Many digital reverb units allow the reverb to be gated.

Noise Gate Controls 

Threshold

The threshold sets the level at which the gate opens and closes.

Attack

The attack determines how quickly the gate opens. Measured in milliseconds

Release

The release determines how quickly the gate closes. Measured in milliseconds

Hold

The hold control determines how long the gate is kept open for after the signal falls below the threshold level, and helps to ensure that a decayed proportion of a sound is not cut off.

Range

The range control turns a signal down that is under the threshold instead of muting it completely.