Dichotic Presentation for Binaural Hearing Aids Using Perceptually Balanced Critical Bandwidth Based Comb Filters

Splitting of speech using comb filters with complementary magnitude response and presenting them to the two ears has helped in improving the perception of speech in sensorineural hearing impaired persons. The pair of comb filters with 18 bands based on auditory critical bandwidths over 5 kHz band, were designed initially with sharp transition between pass and stop bands. Further these filters were optimized to obtain minimum perceived spectral distortion and perceptual balance of intensity at band crossovers. Such comb filters, realized as 256-coefficient linear phase FIR filters, with pass band ripple of 1 dB, stop band attenuation of 30 dB, transition width of 78 to 117 Hz and filter magnitude responses at crossovers adjusted to lie between 4 and 6 dB, provided better recognition scores than that with sharp transitions, when tested on normal subjects with simulated hearing loss. Present investigation involves evaluation of spectral splitting scheme with comb filters with sharp transitions and with perceptually balanced comb filters on bilateral sensorineural hearing-impaired subjects. Further evaluation was conducted by incorporating an additional filter, which partially compensates for the frequency dependent shift in hearing thresholds. The results show improvement of recognition scores, and reception of consonantal features particularly place, frication and duration, with maximum improvement for the combined scheme.