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1/181.Intro 2. Implementation 3. Results 4. Con.

11th IEEE India Conference, INDICON 2014, 11-13 Dec. 2014, Pune, India

FPGA-Based Implementation of Comb Filters Using Sequential Multiply-

Accumulate Operations for Use in Binaural Hearing Aids

byS. G. Kambalimath, P. C. Pandey

P. N. Kulkarni, Mahant-Shettiand S. G. Hiremath

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2/181.Intro 2. Implementation 3. Results 4. Con.

11th IEEE India Conference, INDICON 2014, 11-13 Dec. 2014, Pune, India

PRESENTATION OUTLINE

1 Introduction

2 Implementation

3 Results

4 Conclusion

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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.

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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.

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11th IEEE India Conference, INDICON 2014, 11-13 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 implementingMultiplexer, control logic, and clock generator.

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11th IEEE India Conference, INDICON 2014, 11-13 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.

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 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 0.098 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

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11th IEEE India Conference, INDICON 2014, 11-13 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 combina tional functio

ns

Dedicated

logic registe

rs

Embedded 9-bit multipliers

Total logic eleme

nts

Total combinati

onal functions

Dedicated

logic registe

rs

Embedded 9-bitmultipliers

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

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11th IEEE India Conference, INDICON 2014, 11-13 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

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11th IEEE India Conference, INDICON 2014, 11-13 Dec. 2014, Pune, India

THANK YOU