Shankarayya G. Kambalimath 1 , Prem C. Pandey 2 , Pandurangarao N. Kulkarni 3 ,

1. Paper No. 531 FPGA Based Implementation of Comb Filters for Use in Binaural Hearing Aids for Reducing Intraspeech Spectral Masking Shankarayya G. Kambalimath1, Prem C. Pandey2, Pandurangarao N. Kulkarni3, Shivaling S. Mahant-Shetti4, Sangmesh G. Hiremath5 1,3BEC,Bagalkot; 2IITB, Mumbai; 4KarMic, Manipal; 5GMIT, Davangere 1 kambalimathsg @rediffmail.com 2pcpandey@ee.iitb.ac.in 3pnk_bewoor@yahoo.com Abstract − 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 16-bit 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. • 1. INTRODUCTION • Sensorineural hearing loss • Elevated hearing thresholds • Decreased dynamic range and abnormal loudness growth • Increased temporal & spectral masking • Binaural Dichotic Presentation Using Complementary Comb Filters for Persons Using Binaural Hearing Aids [Lyregaard, 1982; Lunner et al., 1983; Kulkarni et. al, 2012] • Spectral components likely to mask or get masked by each other are presented to different ears, for reducing the adverse effect of increased intraspeech spectral masking and improving speech perception. • Auditory Critical Band Based Perceptually Balanced Comb Filter Pair [Kulkarni et el., 2012] • Filter responses: magnitude responses designed for perceptually balanced loudness, linear phase responses. • Results of test on hearing impaired listeners: (i) 14 – 31% increase in consonant recognition, (ii) 0.26 s decrease in response time, (iii) no adverse effect on the localization of broadband sounds. • Magnitude responses of comb filter pair with floating-point coefficients & offline implementation [Kulkarni et el., 2012]. • Research Objective: Implementation of comb filter pair as the first step for its use in binaural hearing aids. 2. FPGA BASED IMPLEMENTATION Platform Altera Cyclone II EP2C70F896C6 Implementation of a comb filter interfacing to audio codec through I2C. Filters 513-coeff. FIR filters designed using iterative frequency sampling, floating- A binaural hearing aid using comb filters point coefficients scaled to 15-bit sign-magnitude integers (using Altera MegaWizard plug-in manager FIR compiler 9.1) 3. RESULTS Magnitude responses of implemented comb filter pair 4. CONCLUSION FPGA Based Implementation of Comb Filters Resource use of Cyclone II EP2C70F896C6: 47% combinational functions, 34% logic registers, 53% logic elements. Future Work Integration with automatic volume control and frequency-selective response; ASIC design.