Patent ID: 7177805

Claim:
A method for reducing noise in a sampled acoustic signal, comprising: receiving a stream of sampled acoustic signals; digitizing each sampled acoustic signal thereby forming digital samples; selecting a fixed number of digital samples; multiplying the digital samples by a windowing function; computing the fast Fourier transform of the selected windowed digital samples to yield transformed windowed signals; selecting half of the transformed windowed signals; calculating a power estimate of the transformed windowed signals; calculating a smoothed power estimate by smoothing the power estimate over time using the equation: P t ( i )=(1− a ) P t−1 ( i )+ aP ( i ) where: P t (i) is the smoothed power estimate for a current time sample to be calculated for the i-th FFT point; P t−1 (i) is the smoothed power estimate for an immediately prior time sample for the i-th FFT point; P(i) is the calculated power estimate of the transformed windowed signals for the i-th FFT point; and a is an experimentally chosen pre determined value called the smoothing factor; calculating a noise estimate; calculating a gain function from the noise estimate and the smoothed power estimate; calculating a transformed speech signal by multiplying the gain function with the transformed windowed signal; calculating an inversed fast Fourier transform of the transformed speech signal to yield a sampled speech signal; and adding the sampled speech signal to a portion of the speech signal of a previous frame.