Patent ID: 6351731
Filing Date: 2002-02-26
Classification: G10L

Abstract:
An adaptive filter for removing noise from an input signal comprising a digitally sampled audio signal containing speech and added noise, the adaptive filter comprising:a signal divider for generating a spectral signal representing frequency spectrum information for individual time frames of the input signal; a magnitude estimator for generating an estimated spectral magnitude signal based upon the spectral signal for individual time frames of the input signal; a speech spectrum estimator receiving as input the estimated spectral magnitude signal for a time frame and generating an estimated speech spectral magnitude signal representing estimated spectral magnitude values for speech in a time frame; a spectral gain generator that receives as input the estimated spectral magnitude signal and the estimated speech spectral magnitude signal and generates as output an initial spectral gain signal that yields an estimate of speech spectrum in a time frame of the input signal when the initial spectral gain signal is applied to the spectral signal; a spectral gain modifier that receives as input the initial spectral gain signal and generates a modified gain signal by limiting a rate of change of the initial spectral gain signal with respect to the spectral gain over a number of previous time frames; a multiplier for multiplying the spectral signal by the modified gain signal to generate a speech spectrum signal; a channel combiner coupled to the multiplier for converting the speech spectrum signal to a time domain speech signal; and a speech activity detector that generates an output which indicates that speech is either present during a time frame or not present during a time frame, and wherein the spectral gain modifier limits to a greater degree the rate of change of the initial spectral gain signal during time frames for which speech activity detector output indicates that speech is not present as opposed to time frames during which the speech activity detector output indicates that speech is present.