Speech enhancement by maintaining phase continuity

The aim of speech enhancement algorithms is to increase the quality and intelligibility of noise degraded speech signals. Classical algorithms make modifications in the magnitude spectrum of the noise degraded signal and leave the phase spectrum unchanged. Leaving the phase spectrum unchanged relies on the results of the early listening tests, in which it is concluded that a better phase estimation does not have a significant effect on speech quality. However, a poor phase estimate causes a noticeable distortion in the reconstructed signal. It is also shown that (statistically) the optimum estimate for the clean phase is the noisy phase itself (if no additional information is used). In this work a phase estimation method for certain frequency bins is proposed, which exploits the harmonic structure of voiced speech. This method is then incorporated into classical (magnitude based) enhancement algorithms and a new enhancement method is put forward. The performance of the proposed enhancement method is tested with the ITU-T standard PESQ measure and the results are presented.