Patent ID: 8135148
Filing Date: 2012-03-13
Classification: G10L,H03G,H04M

Abstract:
1. An automatic gain control unit for controlling the gain applied to an input signal produced by a microphone subject to ambient noise, wherein said input signal is passed through a codec having analog and digital gain control inputs for varying the analog and digital gain respectively each in increments of a first size and a second size, said second size being smaller than said first size, and said input signal having a signal level, said automatic gain control unit continually monitoring the signal level of said input signal, and comprising: a first comparator for determining when the input signal level exceeds a high threshold; a second comparator for determining when the input signal level falls below a low threshold; a third comparator for determining when said the digital gain exceeds a set threshold; a first gain controller for generating a first control signal to vary the analog gain of the codec in increments of said first size; a second gain controller for generating a second control signal to vary the digital gain of the codec in increments of said second size; wherein said first gain controller is configured to decrease the analog gain of the codec in response to said first comparator determining that said input signal level exceeds said high threshold, and wherein in response to the input signal level falling below said low threshold in the presence of a speech signal said second gain controller is configured to increase the digital gain of said codec, and wherein in response to the input signal level falling below said low threshold in the presence of a speech signal and the digital gain being above said set threshold, said first and second gain controllers are configured to increase the analog gain and decrease the digital gain of the codec such that the increase in analog gain compensates fir the decrease in digital gain.