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Abstract

A system which performs automatic gain control on received audio data. The system comprises an adjustable gain amplifier coupled to a gain control loop which is preferably a digital signal processor. The gain control loop comprises a zero-crossing detector which receives the audio output signal and generates a zero crossing output upon detection of a zero crossing. The gain control loop further comprises a gain adjustment scheduler which receives the zero crossing output and a gain adjustment signal. The gain adjustment scheduler advantageously adjusts the gain of the output signal in incremental steps near zero crossings so as to minimize distortion and the possibility of clipping of the input signal. The gain control loop further comprises a voice activity detector which detects substantial voice activity, wherein the automatic gain control system amplifies the audio input signal only during the substantial voice activity. The voice activity detector thus enables the system to suppress noise amplification during periods of silence. The amplifier has an associated gain range. The control loop further comprises a gain limiter which provides the gain adjustment signal to the gain adjustment scheduler according to the gain range of the amplifier.

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First Claim