Improved spectral subtraction for speech enhancement

The spectral subtraction approach has become almost standard in speech enhancement because it is relatively easy to understand and implement. The major drawback of the spectral subtraction method is that it leaves residual noise with annoying noticeable tonal characteristics referred to as musical noise. For low SNR the perceived effect of the "musical noise" is close to that of the additive noise. In the present work we propose to reduce the musical noise by applying the output of a standard spectral subtractor to a constrained high order notch filter which suppresses the "musical noise". The filtration process distorts the speech signal. It is possible to reduce the level of distortion if the speech signal is preprocessed properly before it is contaminated by the noise. It will be demonstrated that the proposed method is superior to the standard spectral subtraction specially for low SNR. A comprehensive listening test indicated that for segmental SNR= −12dB, 77% of the listeners strongly preferred the proposed approach over the usual spectral subtraction approach.