A noise-reduction strategy for speech based on phase-opponency detectors

Abstract

A noise-reduction algorithm was developed based on a neural model for detection that is robust in fluctuating noise. The phase-opponency (PO) neural model correlates the outputs of two different auditory filters that differ in phase by 180 degrees at the target frequency. The PO detector used here consists of a pair of overlapping bandpass filters with phase responses that differ by 180 degrees near the center frequency (CF). The correlation between the filter responses is reduced when a narrowband signal near CF is present in a noisy background. A bank of PO detectors was used to process speech corrupted by additive Gaussian noise. The time-varying outputs of the detectors can be post-processed to retain information-rich regions, such as formants and frication onsets, while greatly reducing noise between formants. The final detector output controlled the gains in a separate analysis/synthesis filterbank. Spectrograms of speech sounds before and after noise reduction illustrate the ability of the system to detect major features in speech down to low signal-to-noise ratios. The quality of the processed signal will be demonstrated. This system is intended as a front-end for speech recognition systems or in hearing-aid noise-reduction algorithms. [Work supported by NSF BCS0236707 (OD,CYE) and NIH DC-001641 (MCA,LHC).]

Speech enhancement using the modified phase-opponency model

“…4 shows three such BPFs for a MPO structure that can be used to distinguish narrowband signals centered at 1000 Hz with bandwidth less than 250 Hz from wideband noise signals. Initial versions of the MPObased speech enhancement scheme (Deshmukh and Espy-Wilson, 2005;Deshmukh et al, 2005a) used BPFs with passband symmetry across the CF of the MPO structure. Fig.…”

“…In the initial version of the MPO-based speech enhancement scheme (Deshmukh and EspyWilson, 2005;Deshmukh et al, 2005a), each of the MPO i in Fig. 8 consisted of a symmetric BPF and the APF was configured so that signals with bandwidths less than or equal to 150 Hz would lead to negative outputs.…”