Patent ID: 7366658

Claim:
A method of pre-processing speech input signals for noise comprising the steps of: forming a Fast Fourier transform of sampled speech input signals transforming said sampled speech input signals from time domain to frequency domain; filtering said frequency domain data into a plurality of adjacent frequency channels spanning a range of frequencies of human speech; forming an energy estimate for each channel; smoothing said energy estimate for each channel by weighted summing of a current energy estimate for said channel and a prior smoothed energy estimate for said channel as follows SE Chi,n =α*E Chi,n +(1−α) SE Chi,n−1 where: SE Chi,n is the smoothed energy estimate for channel i at time n; E Chi,n is the current energy estimate for channel i at time n; and α is an adaptive smoothing constant; forming a signal to noise ratio estimate for said channel dependent upon a corresponding smoothed energy estimate; forming a voice metric for each channel dependent upon a corresponding signal to noise ratio estimate; and forming a channel gain for each channel dependent upon a corresponding voice metric; wherein said smoothing said energy estimate for each channel moves said adaptive smoothing constant toward a first smoothing constant if said prior signal to noise ratio estimate for more than a predetermined number of channels is above a signal to noise ratio threshold and moves said adaptive smoothing constant toward a second smoothing constant less than or equal to said first smoothing constant if said prior signal to noise ratio estimate for less than said predetermined number of channels is above said signal to noise ratio threshold, and said adaptive smoothing constant is determined as follows: if said prior signal to noise ratio estimate for more than said predetermined number of channels is above said signal to noise ratio threshold then α=0.25*α+0.75*α1 else α=0.25*α+0.75*α2 where: α is said adaptive smoothing constant; α1 is said first smoothing constant; and α2 is said second smoothing constant.