Processing of noisy speech using modified group delay functions

A novel method of processing noisy speech is presented. The method exploits the properties of the negative derivative of the Fourier transform phase spectrum (group delay function) to derive the features of the vocal tract system and the excitation from the speech signal. The key idea used is that the properties of group delay functions for noise and a stable all-pole filter are distinct. Estimation of the spectrum of the vocal tract system and fundamental frequency are treated as problems of spectrum estimation from noisy data. Results of these studies show that intelligible speech can be synthesized from parameters derived from noisy data with an overall signal-to-noise ratio (SNR) as low as 3 dB