A noise reduction device through which an audio signal is passed. When the signal level is very small, the noise gate will close, eliminating any residual noise that may be riding on the signal. In the presence of a signal, the noise gate will open, allowing both signal and noise to pass through, as under these conditions, the noise is masked by the signal. A noise gate is a special type of expander with an infinite expansion ratio below a preset threshold. The effectiveness is determined by the time constants associated with the gain reduction, and often the background noise can be heard switching on and off with the signal. See breathing, gate, floor.