Level variations in speech: Effect on masking release in hearing-impaired listeners

Abstract

Acoustic speech is marked by time-varying changes in the amplitude envelope that may pose difficulties for hearing-impaired listeners. Removal of these variations (e.g., by the Hilbert transform) could improve speech reception for such listeners, particularly in fluctuating interference. Léger, Reed, Desloge, Swaminathan, and Braida [(2015b). J. Acoust. Soc. Am. 138, 389–403] observed that a normalized measure of masking release obtained for hearing-impaired listeners using speech processed to preserve temporal fine-structure (TFS) cues was larger than that for unprocessed or envelope-based speech. This study measured masking release for two other speech signals in which level variations were minimal: peak clipping and TFS processing of an envelope signal. Consonant identification was measured for hearing-impaired listeners in backgrounds of continuous and fluctuating speech-shaped noise. The normalized masking release obtained using speech with normal variations in overall level was substantially less than that observed using speech processed to achieve highly restricted level variations. These results suggest that the performance of hearing-impaired listeners in fluctuating noise may be improved by signal processing that leads to a decrease in stimulus level variations.

Masking release for hearing-impaired listeners: The effect of increased audibility through reduction of amplitude variability

“…Similar effects of positive MR PCT , again tempered by a corresponding decrease in continuous-noise performance compared to unprocessed speech, were observed by Reed et al (2016) for two other types of processing which effectively removed variations in amplitude of the speech signal. These methods included infinite peak clipping to achieve a reduction in amplitude variation similar to that present in TFS speech and a 40-band envelope signal that was reprocessed with Hilbert-transform-based TFS processing to remove the amplitude variations.…”

“…The advantage of EEQ processing over peak-clipping is that it does not introduce major distortions due to the processing itself. Evidence of the greater distortions present in peak-clipping compared to EEQ processing is seen by its lower performance compared to UNP speech in continuous noise backgrounds at a given SNR (see Reed et al, 2016), whereas no significant differences were observed between CON scores for EEQ and UNP speech (see left panel of Fig. 3 above).…”

“…This research derives from previous studies which suggest that the amplitude variations present in the speech signal may play a role in determining the size of masking release in HI listeners (L eger et al, 2015;Reed et al, 2016). Specifically, by reducing amplitude variation for speech in interrupted noise, the audibility of lower-energy speech present in the noise dips is increased leading to higher intelligibility.…”

“…The practicality of the techniques that yielded positive MR PCT in both L eger et al (2015) and Reed et al (2016) is limited by the fact that the increase in MR PCT resulted from a decrease in speech intelligibility in continuous noise as opposed to an increase in intelligibility in interrupted noise. This decrease in continuous-noise speech intelligibility is largely due to distortions introduced by TFS processing and peak clipping.…”

Effect of Energy Equalization on the Intelligibility of Speech in Fluctuating Background Interference for Listeners With Hearing Impairment

“…Previous studies of Léger, Reed, Desloge, Swaminathan, and Braida (2015) and Reed, Desloge, Braida, Léger, and Perez (2016) suggest that MR for listeners with HI may be enhanced by processing methods which lead to a reduction of the normal level variations present in speech. In these two studies, however, the improvements in MR arose primarily from decreased performance in continuous background noise relative to that in interrupted noise, due to distortions introduced by the signal processing.…”