Automatic gain control for mobile microphone

Abstract

An automatic gain control unit controls the gain applied to an input signal produced by a microphone subject to ambient noise. The automatic gain control circuit continually monitors the signal level of said input signal. A first gain control circuit decreases the gain applied to the input signal in increments of a first size when the input signal exceeds a first predetermined level. A second gain control circuit increases the gain applied to said input signal in increments of a smaller size when the input signal falls below a second predetermined level and in response to the presence of a speech present signal. The second predetermined level is less than said first predetermined level. In one embodiment, the first gain control circuit controls the analog gain of a codec and the second gain control circuit controls the digital gain of the codec.

Description

technical field [0001] The invention relates to a microphone, in particular to a method for controlling the gain of the microphone, which is suitable for the microphone of a mobile phone. Background technique [0002] In communication systems, echo is a phenomenon in which delayed and distorted versions of the original signal are reflected back to the source of the signal. In telephone systems, echoes cause impairment of speech signal fidelity and are often detrimental to users. To this end, telephone systems typically provide echo cancellers, which attempt to eliminate echoes. To do this, the echo canceller generates an echo replica based on an estimate of the echo signal path and subtracts it from the input signal. In Fig. 1, the received signal r(n) is used as a reference signal. This signal is emitted by the loudspeaker and picked up by the microphone as an echo signal along with the desired signal. The echo generator produces an estimate of this signal e(n), which i...

AI Technical Summary

Problems solved by technology

The echo canceller will not work well if the echo path keeps changing

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