Optimizing the sweep cycle of time-varying comb filters for binaural dichotic presentation in sensorineural hearing impairment

Abstract

Splitting of speech into two using time-varying comb filters has helped in reducing the effect of increased temporal and spectral masking simultaneously. The time varying comb filters contained pre-calculated sets of coefficients, which were selected in steps, such that a cyclic sweeping of magnitude responses occur. Presently the investigation has been carried out to find the best sweep cycle. The two sets of coefficients selected at any instant of time formed a pair of complementary comb filters with 18 auditory critical bands which provided spectral separation of components that are likely to get masked. Sweeping of the bands provides temporal separation and reduces the effect of temporal masking. As the number of magnitude responses swept increases, the sweeping becomes smoother. The sweep cycle duration determines the time for which the sensory cells of the basilar membrane remain stimulated. Perception evaluation tests were conducted with slowly sweeping sine wave and running speech from a male and a female speaker for sweep cycles of 10, 20, 40, 50, 60, 80, and 100 ms. The best results were obtained for a sweep cycle of 50 ms.