Practical Gammatone-Like Filters for Auditory Processing
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Research Article Practical Gammatone-Like Filters for Auditory Processing A. G. Katsiamis,1 E. M. Drakakis,1 and R. F. Lyon2 1 Department
of Bioengineering, The Sir Leon Bagrit Centre, Imperial College London, South Kensington Campus, London SW7 2AZ, UK 2 Google Inc., 1600 Amphitheatre Parkway Mountain View, CA 94043, USA Received 10 October 2006; Accepted 27 August 2007 Recommended by Jont B. Allen This paper deals with continuous-time filter transfer functions that resemble tuning curves at particular set of places on the basilar membrane of the biological cochlea and that are suitable for practical VLSI implementations. The resulting filters can be used in a filterbank architecture to realize cochlea implants or auditory processors of increased biorealism. To put the reader into context, the paper starts with a short review on the gammatone filter and then exposes two of its variants, namely, the differentiated all-pole gammatone filter (DAPGF) and one-zero gammatone filter (OZGF), filter responses that provide a robust foundation for modeling cochlea transfer functions. The DAPGF and OZGF responses are attractive because they exhibit certain characteristics suitable for modeling a variety of auditory data: level-dependent gain, linear tail for frequencies well below the center frequency, asymmetry, and so forth. In addition, their form suggests their implementation by means of cascades of N identical two-pole systems which render them as excellent candidates for efficient analog or digital VLSI realizations. We provide results that shed light on their characteristics and attributes and which can also serve as “design curves” for fitting these responses to frequency-domain physiological data. The DAPGF and OZGF responses are essentially a “missing link” between physiological, electrical, and mechanical models for auditory filtering. Copyright © 2007 A. G. Katsiamis et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
For more than twenty years, the VLSI community has been performing extensive research to comprehend, model, and design in silicon naturally encountered biological auditory systems and more specifically the inner ear or cochlea. This ongoing effort aims not only at the implementation of the ultimate artificial auditory processor (or implant), but also to aid our understanding of the underlying engineering principles that nature has applied through years of evolution. Furthermore, parts of the engineering community believe that mimicking certain biological systems at architectural and/or operational level should in principle yield systems that share nature’s power-efficient computational ability [1]. Of course, engineers bearing in mind what can be practically realized must identify what should and what should not be blindly replicated in such a “bioinspired” artificial system. Just as it does not make sense to create fla
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