Critical band splitting of speech signal for reducing the effect of spectral masking in bilateral sensorineural hearing impairment

Persons with sensorineural hearing impairment face a particular problem in view of decrease in frequency resolving capacity of the auditory system due to spread of spectral masking along the cochlear partition. Filtering speech signal by a filter bank and adding signals from alternate bands and presenting it to the two ears is likely to reduce the effect of spectral masking and thus improving the speech intelligibility. The scheme was implemented in real time processing for use as a binaural hearing aid. Processing for each channel is done by a linear phase FIR filter having a magnitude response with pass bands corresponding to alternate critical bands, the magnitude response for the two channels being complemented. For both the filters, the magnitude response was approximated with 128 coefficients using a frequency sampling technique of linear phase FIR filter design. The implementation was done on two TI/TMS320C50 based DSP boards, each having 14-bit ADC and DAC. Twelve English consonants were used for carrying out listening tests in vowel-consonant-vowel (VCV) and consonant-vowel (CV) syllables presented to six hearing impaired subjects with bilateral sensorineural hearing loss. Information transmission analysis of confusion matrices for various features show maximum improvement for the place feature.