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Adaptive Signal Processing pp 23–57Cite as

Adaptive Feedback Cancellation in Hearing Aids

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Part of the book series: Signals and Communication Technology ((SCT))

Abstract

In feedback cancellation in hearing aids, an adaptive filter is used to model the feedback path. The output of the adaptive filter is subtracted from the microphone signal to cancel the acoustic and mechanical feedback picked up by the microphone, thus allowing more gain in the hearing aid. In general, the feedback cancellation filter adapts on the hearing-aid input signal, and signal cancellation and coloration artifacts can occur for a narrowband input. The goal in feedback cancellation is to design an algorithm that is computationally efficient, provides 10 dB or more of additional amplifier headroom, and is free from processing artifacts.

This chapter begins with a steady-state analysis of the effects of acoustic feedback on the hearing-aid response. This analysis illustrates the factors that can affect the accuracy of the adaptive filter and the filter convergence for systems adapting with or without a probe signal. The characteristics of the feedback path being modeled are then described. An additional concern in designing signal processing for a hearing aid are the processing constraints imposed by a low-power portable device, and these concerns are discussed next. Two forms of constrained adaptation are then derived, and simulation results are used to give a comparison of the constrained adaptation with the conventional unconstrained approach for a system adapting without a probe signal. Further improvements in feedback cancellation performance, particularly a reduction in audible processing artifacts, can be achieved by using the filtered-X algorithm, and this approach is described next.

The performance of feedback cancellation is ultimately limited by the characteristics of the room in which the listener is located since the room reflections form part of the feedback path. The chapter concludes with a study of the feedback path in a room along with the feedback cancellation performance for an 8-, 16-, or 32-tap adaptive FIR filter in series with a five-pole nonadaptive filter, and the performance limitations imposed by the room reverberation are discussed.

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Author information

Authors and Affiliations

  1. Cirrus Logic, AudioLogic Design Center, 2465 Central Avenue, Suite 100, Boulder, CO, 80301, USA

    James M. Kates

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  1. James M. Kates
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Editors and Affiliations

  1. Bell Labs, Lucent Technologies, 700 Mountain Avenue, 07974-0636, Murray Hill, NJ, USA

    Jacob Benesty  & Yiteng Huang  & 

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© 2003 Springer-Verlag Berlin Heidelberg

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Kates, J.M. (2003). Adaptive Feedback Cancellation in Hearing Aids. In: Benesty, J., Huang, Y. (eds) Adaptive Signal Processing. Signals and Communication Technology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-11028-7_2

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  • DOI: https://doi.org/10.1007/978-3-662-11028-7_2

  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-642-05507-2

  • Online ISBN: 978-3-662-11028-7

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