Design and synthesis of filter bank structures based on low order constrained least square and minimum phase methods for

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ORIGINAL PAPER

Design and synthesis of filter bank structures based on low order constrained least square and minimum phase methods for audiogram matching in digital hearing aids V. V. Mahesh1 · T. K. Shahana1 Received: 17 April 2020 / Accepted: 19 October 2020 © IUPESM and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Frequency decomposer or filter bank plays acritical role in the design of digital hearing aid systems.This paper proposes filter bank structures suitable for the design of optimal hearing aid systems.The performance indices such as complexity, power dissipation, area utilization, delay, matching error of the filter banks are very competitive when compared to the designs in literature.Constrained least square finite impulse response filter with smooth transition band characteristics is used in the first method.The second method is based on Minimum phase filters with reduced number of coefficients which exhibit the smallest passband group delay in the family of filters with the same magnitude response characteristics.Hardware complexity is reduced very much since there is significant reduction in multiplications per sample in both the methods.Full cycle responses of individual filters are considered for calculation of overall response of the filter bank.Coefficient decimation method is used in the reconfigurable structure to enable the filter banks to adapt variation in audiogram pattern during the course of time.Synthesis results by Cadence Encounter(R.) R.T.L. Compiler software also justify the theoretical claims Keywords  Constrained least square filters · Minimum phase filters · Finite impulse response filter bank · Coefficient decimation · Audiogram

1 Introduction Hearing aids improve the speech intelligibility by rectifying hearing loss with auditory compensation methods [1]. Low cost hearing aids are still need of the day as millions of hearing loss cases are reported from the under developed countries and World Health Organization (WHO) studies reveals that, around 10% of the affected are children [2]. Hardware complexity of hearing aid device should be reduced to manufacture the item in a large volume at a lower cost, affordable by the poor. In digital hearing aid design, filter banks play a critical role. A filter bank decomposes the input signal in to frequency bands which may be processed independently to best compensate for the hearing loss. A * V. V. Mahesh [email protected] T. K. Shahana [email protected] 1



Division of Electronics Engineering, School of Engineering, Cochin University of Science and Technology, Kochi, India

person with impaired hearing tends to have a low sensitivity towards certain frequencies and the filter bank should be able to adjust sound levels at arbitrary frequencies within a given spectrum. This is achieved by passing input signal from microphone through a set of filters that divides audio signals in to different frequency bands. The gains of each sub band filters are adjustable to match the audiogram of the hearing impaired