Improving harmonic selection for speech intelligibility enhancement by the reassignment method

Harmonic selection is a useful mechanism for speech enhancement. However, there is difficulty in detecting harmonic structure in the spectrum in the presence of noise or interfering speech. In this paper we address the problem of applying the reassignment method to produce a higher-resolution spectrum for improving the harmonic selection. The reassignment method is to assign the value of the spectrogram computed by the short-time Fourier transform to the gravity center of the region rather than the geometric center of the region. We analyze the resolution capability of the reassigned Fourier spectrum and show that it has better frequency separation than Fourier spectrum. We incorporate the reassignment method with the amplitude-modulation based harmonic selection to segregate a target vowel from interfering vowels. Experimental results show that the target vowel recognition performance is improved by using the reassignment method for increasing the readability of the harmonic structure in speech signals.