Speech enhancement by non-stationary tonal disturbance cancellation using subband zero crossing measures

A time domain based method for rejection of tonal disturbances in speech signals is presented. Tonal disturbances in personal communication arise in a variety of situations such as environmental sounds from rotating machinery, acoustic feedback in PA-systems or hearing aids and internal circuitry of some personal communication devices. The method is based on the zero crossings of subband signals. After splitting the disturbed signal into subbands, the distances between zero crossings in the subband signals are measured. A low distance spread indicates that a tonal component is dominating the subband signal. This distance spread is then used to steer a gain function that adaptively and continuously attenuates subbands in which tonal components are dominant. The method has proven to be effective on stationary as well as non-stationary disturbances with reasonable amount of speech signal distortion.