Speech enhancement for noise-robust speech recognition.

Abstract

A modified phase opponency (MPO) model was combined with the aperiodic/periodic/pitch detector (APP) by Deshmukh et al. [JASA, 121, 3886–3898 (2006)] for speech enhancement. The MPO-APP passes the speech-dominated regions as is but greatly attenuates the noise-dominated regions. Thus, the noise in nonspeech regions and in the regions between the formants are significantly reduced. Unlike many other techniques, the MPO-APP does not introduce musical noise. However, given that the noise in formant regions is passed along with the speech signal, the enhanced signal sometimes has a shadow effect. To get rid of this shadow effect, we recently developed a preprocessor for the MPO-APP. First, the signal to noise ratio of the signal is estimated. Second, we use an adaptive generalized spectral subtraction technique to reduce the noise in the speech dominant regions. The results show a significant improvement in the quality of the enhanced signal and, in addition, increased accuracy in automatic recognition of the enhanced signals over that obtained from the original signals or the signals enhanced without the preprocessor. [Research supported by NSF Grant IIS0703859.]