For instance, inexpensive computer sound cards emit a lot of hiss that is very noticable when the sound system is otherwise quiet. Also, microphones may pick up background noise that could prove to be distracting when played through a large sound system. These problems can be mostly eliminated by using devices known as noise gates . A noise gate will not pass an audio signal through it unless it is above the threshold level , set by a knob on the front of the unit. Once the sound level rises above the level set by the threshold knob, the gate opens, allowing the input signal to pass through it.
Additional controls adjust how quickly the gate opens and closes.
Some gates do not actually shut off the sound, but they reduce it by some amount. These gates have an additional control to adjust how much reduction is used when the gate is closed. Generally, a noise gate is inserted into a problem channel and adjusted such that the threshold level is set to be above the background noise. The end result is silence from the channel when there is just background noise from the input, and the normal signal when a level higher than the threshold is present. Specifically, no warranty is expressed or implied regarding the accuracy of the information contained within.