Harmonic Enhancement with Noise Reduction of Speech Signal by Comb Filtering

As single channel speech enhancement, common me- thods based on short-time spectral amplitude estimation such as spectral-subtraction and wiener filtering are considered to be simple and effective for suppressing the additive noise in noisy environments. However, these techniques may distort the high frequency harmonics of speech, which are important to the lan- guage understanding. To solve this problem, we propose a new approach. It works by using a comb filter in time domain after wiener filtering. With the harmonics of voiced speech enhanced and most of the noise suppressed, another comb filter in frequen- cy domain is used to recalculate the suppression gain function, renewing the high frequency harmonics that have been com- pressed. This new method is theoretically derived, and experi- mentally demonstrates an improvement for harmonic enhance- ment and noise reduction. In this paper, we propose a new method. It uses a classical wiener filter first. Then a comb filter in time domain based on accurate pitch estimation is used to enhance the voiced speech harmonics and reduce the noise. After that, an improved har- monic regeneration method is processed in frequency domain to recover the harmonics which have been destroyed. The wiener filtering ensures the accuracy of pitch estimation for the comb filter, and the comb filtering further suppresses the resi- dual noise after wiener filtering and improves the performance of the harmonic recovering. This new method can be potential- ly combined with previous algorithms but performs better than either one separately for enhancing the sound quality and speech clarity. We believe the proposed method has both theo- retical and practical merits.