The results show that dichotic presentation may be useful for speech processing in binaural hearing aids.

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Sensorineural hearing loss is associated with widening of auditory filter bandwidths, leading to increased spectral masking and degraded speech perception. Multiband frequency compression can be used for reducing the effects of spectral masking. In this technique, the speech spectrum is divided into a number of analysis bands and spectral samples in each of these bands are compressed towards the band center by a constant compression factor. Implementation of the scheme with different types of frequency mappings, bandwidths, and segmentation for processing is investigated. Listening tests conducted for assessing the quality and intelligibility of the processed speech gave best results for critical bandwidth based compression using spectral segment mapping and pitch-synchronous processing.

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In a previous investigation [P. C. Pandey et al., J. Acoust. Soc. Am. 110, 2705 (2001)], a scheme using binaural dichotic presentation was devised for simultaneously reducing the effect of increased temporal and spectral masking in bilateral sensorineural hearing impairment. Speech was processed by a pair of time-varying comb filters with passbands corresponding to cyclically swept auditory critical bands, with the objective that spectral components in neighboring critical bands do not mask each other and sweeping of filter passbands provides relaxation time to the sensory cells on the basilar membrane. Presently investigation is carried out to find the optimal value of the sweep cycle. Comb filters used were 256-coefficient linear phase filters, with transition crossovers adjusted for low perceived spectral distortion, 1 dB passband ripple, 30 dB stopband attenuation, and 78–117 Hz transition width. Acoustic stimuli consisted of swept sine wave and running speech from a male and a female speaker. Bilateral loss was simulated by adding broadband noise with constant short-time SNR. Listening tests with stimuli processed using sweep cycles of 10, 20, 40, 50, 60, 80, 100 ms indicated highest perceptual quality ranking for sweep cycle in the 40–60 ms range, with a peak at 50 ms.