Factors influencing intelligibility of ideal binary-masked speech: Implications for noise reduction

Abstract

The application of the ideal binary mask to an auditory mixture has been shown to yield substantial improvements in intelligibility. This mask is commonly applied to the time-frequency (T-F) representation of a mixture signal and eliminates portions of a signal below a signal-to-noise-ratio (SNR) threshold while allowing others to pass through intact. The factors influencing intelligibility of ideal binary-masked speech are not well understood and are examined in the present study. Specifically, the effects of the local SNR threshold, input SNR level, masker type and errors introduced in estimating the ideal mask are examined. Consistent with previous studies, intelligibility of binary-masked stimuli is quite high even at -10 dB SNR for all maskers tested. Performance was affected the most when the masker dominated T-F units were wrongly labeled as target-dominated T-F units. Performance plateaued near 100% correct for SNR thresholds ranging from -20 dB to 5 dB. We believe the existence of the plateau region suggests that it is the pattern of the ideal binary mask that matters the most rather than the local SNR of each T-F unit. This pattern directs the listener's attention to where the target is and enables them to segregate speech effectively in multi-talker environments.

Speech-cue transmission by an algorithm to increase consonant recognition in noise for hearing-impaired listeners

“…As with the algorithm, it was found that the IBM improved recognition of isolated phonemes, thus extending results observed previously for sentences (Anzalone et al, 2006;Brungart et al, 2006;Li and Loizou, 2008;Wang et al, 2008Wang et al, , 2009Cao et al, 2011;Sinex, 2013). This result should not be surprising, given the effectiveness of algorithm processing observed here and the fact that the algorithm aimed to estimate the IBM.…”

“…This difference is generally obscured when using sentence materials, as IBM scores tend to reach ceiling values (e.g., Brungart et al, 2006;Li and Loizou, 2008;Wang et al, 2009;Sinex, 2013). Another consequence is that the increased effectiveness of IBM processing for HI listeners is reflected with clarity when assessed as the distance between IBM scores and scores in quiet (see Fig.…”

“…The choices made here, with LC about 5 dB smaller than input SNR, were motivated by values shown to be effective for noisy sentences (Brungart et al, 2006;Li and Loizou, 2008;Wang et al, 2009;Kjems et al, 2009). It is possible that LC values that are most effective for consonant materials will differ from those for sentence materials, perhaps due to the increased requirements for acoustic speech information and increased reliance on bottom-up processing.…”

“…In the Ideal Binary Mask (IBM), the premixed speech and noise signals are known, and the mask corresponds to ideal classification. IBM processing produces remarkable speech-intelligibility improvements in noise for both HI and NH listeners, even at extremely low SNRs (Anzalone et al, 2006;Brungart et al, 2006;Li and Loizou, 2008;Wang et al, 2008Wang et al, , 2009Cao et al, 2011;Sinex, 2013).…”

Blind binary masking for reverberation suppression in cochlear implants

“…Binary masking refers to algorithms that decompose the signal into T-F units and select those units satisfying a given criterion (e.g., SNR > 0 dB, for noise suppression), while discarding the rest by applying a binary mask to the units of the decomposed signal, i.e., the mask for a given T-F unit is set to 0 if it does not satisfy a given criterion or is set to 1 if it satisfies the criterion (Wang and Brown, 2006). Binary masks have been widely used for different speech enhancement as well as sound separation applications resulting in gains in intelligibility and quality of the processed noisy speech (Wang and Brown, 2006;Kim et al, 2009;Li and Loizou, 2008). Use of the binary masks for dereverberation, which was only evaluated by a few studies, is attractive as it does not rely on the inversion of the RIR.…”