1/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India FPGA-Based Implementation of Comb Filters Using Sequential Multiply- Accumulate Operations for Use in Binaural Hearing Aids by S. G. Kambalimath, P. C. Pandey P. N. Kulkarni, Mahant-Shetti and S. G. Hiremath

2/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India PRESENTATION OUTLINE 1 Introduction 2Implementation 3Results 4 Conclusion

3/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India 1. INTRODUCTION Sensorineural hearing loss ● Elevated hearing thresholds ● Decreased dynamic range and abnormal loudness growth ● Increased temporal & spectral masking Intro.1/5

4/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India 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. Intro.2/5 A binaural hearing aid using comb filters

5/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India 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. Magnitude responses of comb filter pair with floating-point coefficients & offline implementation. 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. Intro.3/5

6/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Wide-band spectrograms (Δf = 0.3 kHz) of a sentence ‘would you write gun’: (a) diotic, (b) dichotic, processed with a pair of comb filters [Kulkarni et el., 2012] Intro.4/5

7/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Research Objective Efficient FPGA based Implementation of comb filter pair, as the first step for its use in binaural hearing aids, using different architectures. Intro.5/5

8/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Imp.1/4 2. FPGA BASED IMPLEMENTATION FPGA and Audio codec interfacing on FPGA board used for comb filter implementation Comb filter realization as direct-form FIR filter structure.

9/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Comb filter realization as transposed-form linear phase FIR filter structure. FPGA-based implementation of direct-form FIR filter structure using parallel multiply- accumulate operations. Imp.2/4 ▪ Uses (N-1) delays, N multipliers and, (N-1) adders

10/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India FPGA-based implementation of transposed-form linear phase filter structure using parallel multiply- accumulate operation. Imp.3/4 ▪ Explots symmetry in filter coefficients. ▪ No. of multipliers reduced to half as needed in direct form implementation.

11/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India FPGA-based implementation of direct-form FIR filter structure using sequential multiply- accumulate operations. Imp.4/4 ▪ Uses only one adder and one multiplier. ▪ Needs extra resources for implementing Multiplexer, control logic, and clock generator.

12/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Result.1/5 3. RESULTS All the implementations worked satisfactorily for sampling frequency of 10 kHz. Informal listening tests: Binaural presentation of the processed test stimuli showed no perceptual distortion for the processed sounds indicating nearly perfect perceptual fusion of the binaural sounds Magnitude responses of the 257-coefficient comb filters (dark & light for L & R filters) using Direct-form parallel implementation.

13/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Magnitude responses of the 257-coefficient comb filters (dark & light for L & R filters) using transposed form parallel implementation. Magnitude responses of the 257-coefficient comb filters (dark & light for L & R filters) using direct form, sequential implementation. Result.2/5

14/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Magnitude responses of the 513-coefficient comb filters (dark & light for L & R filters) using Direct-form parallel implementation. Magnitude responses of the 513-coefficient comb filters (dark & light for L & R filters) using transposed form parallel implementation. Result.3/5

15/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Magnitude responses of the 513-coefficient comb filters (dark & light for L & R filters) using direct form, sequential implementation. All the filter responses have pass-band ripple below 2 dB and cross-over gains of −4 to −8 dB, stop-band attenuation is greater than 25 dB for 513 coefficient filters and greater than 18 dB for 257-coefficient filter. Deviation in the sum of magnitude responses on a linear scale is below for all responses. The properties of the 513-coefficient FPGA- based comb filters closely match with those reported earlier (Kulkarni et al., 2012) Result.4/5

16/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India Resource Requirements of Different Filter Architectures. Filter Architecture Resources used for 257-coefficient filter Resources used for 513-coefficient filter Total logic eleme nts Total combin a­tional functio ns Dedica ted logic registe rs Embedd ed 9-bit multipli ers Total logic eleme nts Total combinatio nal functions Dedica ted logic registe rs Embedded 9-bit multipliers Earlier work [23] 53%47%34%---- Direct-form, Parallel multiply- accumulate 18%17%12%----32%29%24%---- Transposed- form linear phase, Parallel multiply- accumulate 18%17%12%----32%29%24%---- Direct-form, Sequential multiply- accumulate 15%9%12%<1%30%18%24%1% Result.5/5

17/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India 3. CONCLUSIONS All the implementations worked satisfactorily for sampling frequency of 10 kHz. Implementation using a 16-bit codec, 15-bit signed coefficients, and 32-bit registers resulted in satisfactory filter responses and used only a fraction of resources available on the chip. The filter architecture using sequential multiply-accumulate found more efficient in resource utilization with the scope for implementing other processing blocks of a hearing aid on the same chip. Implementation of prototype hearing aid with dynamic range compression, frequency-selective response, and comb filters can be taken up for developing a hearing aid. FPGA design can be converted to an ASIC for developing wearable hearing aid. Concl.1/1

18/18 1.Intro 2. Implementation 3. Results 4. Con. 11 th IEEE India Conference, INDICON 2014, Dec. 2014, Pune, India THANK YOU