Speech enhancement using robust weighting factors for critical-band-wavelet-packet transform

Although the noise masking threshold (NMT) has been applied in adapting speech enhancement systems, it may suffer from underestimation in low-SNR condition. We derive a robust weighting factor for each wavelet subband. The function of the robust weighting factor is to keep the energy of residual noise lower than the NMT and the speech distortion smaller than the residual noise. If the energy of residual noise is greater than the NMT, the wavelet coefficients (WCs) of noisy speech are suppressed to remove more residual noise. If the energy of residual noise is smaller than the NMT, the weighting factor is set to one to retain speech quality. It results in a lower bound of NMT for preventing the underestimation of weighting factors. Experimental results show that the proposed method can improve the naturalness of enhanced speech.