Effects of the Simultaneous Application of Nonlinear Frequency Compression and Dichotic Hearing on the Speech Recognition of Severely Hearing-Impaired Subjects: Simulation Test
Splitting of speech into two signals by comb filters having complementary magnitude response and presenting these signals to the two ears has helped in improving the perception for persons with bilateral sensorineural hearing loss. Investigation is carried out to improve the comb filters based on auditory critical bands, with the objective of minimizing the perceived spectral distortion. Listening tests were conducted to find the difference in intensity with monaural and binaural presentations for equal loudness perception. Based on the results obtained, 256-coefficient linear phase FIR comb filters were designed using frequency sampling technique, to obtain magnitude response with pass band ripple of 1 dB, stop band attenuation of 30 dB, and crossovers adjusted to lie between −4 dB and −6 dB with respect to pass band response. Listening tests involving closed set identification of 12 vowel-consonant-vowel syllables were conducted, to compare the performance of the new comb filter with the filter with sharp transitions. The new comb filters resulted in a higher improvement of recognition scores and relative information transmission.