Enhancement of speech in noise using multi-channel, time-varying gains derived from the temporal envelope

Abstract

The envelope of speech in noise has been used as a control signal to amplitude-modulate corrupted speech in order to reduce noise and potentially enhance speech quality and intelligibility. In this study, separate speech and noise time histories were mixed at different SNRs to produce time-aligned speech in noise with a range of SNRs. The temporal envelope of the control signal was manipulated by selecting mixtures with the same, or different, SNRs as the signal being controlled. Signals from 200 Hz to 6 kHz were processed into sixteen, parallel contiguous subbands with bandwidths approximating 1.5 times that of auditory filters. The subband envelopes were formed from the absolute value of signals and low pass filtered at 16 Hz. Eleven subjects aged 29 ± 8 years (mean and range) with normal hearing underwent the Modified Rhyme Test to assess speech intelligibility. Speech quality was assessed objectively by PESQ. When the SNRs of the controlling signal and the speech in noise being controlled were the same, no improvement in speech intelligibility was obtained. When the SNR of the controlling signal exceeded that of the signal being controlled, statistically significant increases in mean word scores of up to 36% could be obtained, hence providing an estimate for the maximum improvement in speech intelligibility achievable by reducing noise in the control signal. There were also small improvements in speech quality.