A modified Ephraim-Malah noise suppression rule for automatic speech recognition

A soft decision gain modification is introduced and applied to the Ephraim-Malah gain function based on maximum mean square error estimation (MMSE) (Ephraim, Y. and Malah, D., IEEE Trans. Acoust. Speech Sig. Process., vol.ASSP-32, no.6, p.1109-21, 1984; vol.ASSP-33, no.2, p.443-5, 1985) after amplitude compression. Non-linear evaluations of the noise overestimation factor and spectral floor are used in the same way for the proposed gain modification and for non-linear spectral subtraction (NSS). Consistent and statistically significant ASR improvements of the proposed approach with respect to NSS are observed for different noise conditions considered in the AURORA2 and AURORA3 corpora. As the non-linearity affects the two approaches in the same way, the comparison result is particularly interesting.