FPGA based implementation of comb filters for use in binaural hearing aids for reducing intraspeech spectral masking

Sensorineural hearing impairment is associated with decreased speech perception due to increased intraspeech spectral masking. For persons with moderate bilateral sensorineural loss, binaural dichotic presentation using a pair of complementary comb filters can reduce the effects of increased intraspeech spectral masking and thereby improve speech perception. It has been earlier shown that use of comb filters based on auditory critical bandwidths, with magnitude responses designed for perceptual balance of loudness and linear phase responses, resulted in a significant improvement in speech perception without adversely affecting localization of broadband sound sources. An FPGA-based implementation of these 513-coefficient filters with sampling frequency of 10 kHz is carried out for use in binaural hearing aids. Implementation using a 16bit codec and 15-bit integer filter coefficients used 47%, 34%, and 53% of combinational functions, logic registers, and logic elements, respectively, available on “Altera Cyclone II EP2C70F896C6” FPGA. The resulting magnitude responses have a close match to the offline floating-point implementation.