Real Time Speech Processing for Dichotic Presentation for Binaural Hearing Aids

In case of sensorineural impairment, the reduced frequency resolution in the peripheral auditory system due to spread of masking of a frequency component by adjacent frequency components degrades speech perception. Speech processing by a bank of critical band filters and adding signals from alternate bands for presenting odd numbered critical bands to one ear and even numbered ones to the other is likely to reduce the effect of spread of masking along the cochlear partition, and therefore it may help in improving speech intelligibility. This scheme has been implemented for real-time processing for use as a binaural hearing aid. The implementation consists of two TI/TMS320C50 DSP processor based boards, each having 14-bit ADC and DAC. Speech signal after amplification and signal conditioning is connected as input to both the boards. One board uses filter coefficients corresponding to the even numbered critical bands, and the other board uses filter coefficients for the odd numbered critical bands. For filtering, the FIR filter coefficients for the two channels are loaded to the corresponding DSP boards, using serial port from a PC. Twelve English consonants were used in carrying out listening tests in vowelconsonant-vowel (VCV) syllables presented to a normal hearing subject with simulated sensorineural hearing loss. The test results show an increase of 8 % in the recognition score under adverse listening condition. Information transmission analysis of confusion matrices, for various features, show maximum improvement for the place feature.