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. The range control is used to set the amount of attenuation to be applied to the signal when the gate is closed. Often there will be complete attenuation, that is no signal will pass when the gate is closed. In some circumstances, complete attenuation is not desired and the range can be changed. Advanced gates have an external sidechain. This is an additional input that allows the gate to be triggered by another audio signal. A variation of a sidechained noise gate used in electronic music production is a trancegate or just simply gate, where the noise gate is not controlled by audio signal but a preprogrammed pattern, resulting in a precisely controlled chopping of a sustained sound. Noise gates often implement hysteresis, that is, they have two thresholds: one to open the gate and another, set a few dB below, to close the gate. This means that once a signal has dropped below the close threshold, it has to rise to the open threshold for the gate to open, so that a signal that crosses over the close threshold regularly does not open the gate and cause chattering. A longer hold time also helps to avoid chattering, as described above. Roles The basic function of a noise gate is to eliminate sounds below a given threshold. Noise gates are commonly used in the recording studio and sound reinforcement. Rock musicians may also use small portable "stompbox" units to control unwanted noise from their guitar amplification systems. Band-limited noise gates are also used to eliminate background noise from audio recordings by eliminating frequency bands that contain only static. Audio noise reduction In audio post-processing, noise gating reduces steady noise sources such as rumble from LP records, hiss from audio tape, static from a radio or amplifier, and hum from a power system, without greatly affecting the source sound. An audio signal such as music or speech is broken up into many frequency bands by a collection of overlapping band-pass filters, and if the signal amplitude in any one band is lower than a preset threshold, then that band is eliminated from the final sound. This greatly reduces