Adaptive Postfiltering for Enhancement of Noisy Speech in the Frequency Domain

This paper presents a new frequency-domain adaptive postfilter for enhancement of noisy speech. The postfilter suppresses the noise in spectral valleys and allows more noise in the formant regions where i t is masked by the speech signal. First, we perform an LPC analysis of the noisy speech and calculate its log magnitude spectrum. After identifying the formants and spectral valleys, the log magnitude spectrum is modified to obtain the postfilter frequency response. This response has local minima in the regions corresponding to the spectral valleys and local maximaof equal magnitude a t the formant frequencies. The filtering uses an overlap-add F F T strategy. Experimental results show that this new frequency-domain approach results in enhanced speech of better perceptual quality than obtained by a time-domain method. Our method is especially efficient in eliminating high frequency noise and in preserving the weaker, high frequency formants in sonorant sounds.