Filter Cascades as Analogs of the Cochlea

Abstract

Wave propagation in the cochlea can be modeled as a cascade of transfer functions that characterize local filtering along the place dimension. The Liouville-Green (LG) method connects the design of those transfer functions, or filter stages, to models of the local properties of the physical wave medium, whether those models are based on 1D, 2D, or 3D approaches. Low-order rational filter stages yield useful approximations to the overall cochlear response. Nonlinear effects in the cochlea, including both distortion-product and gain-variation nonlinearities, are easily incorporated as small nonlinear effects in each of the cascaded filters. The filter-cascade approach, however, is not useful for modeling effects of backward propagation, such as otoacoustic emissions. Both analog VLSI and digital implementations of filter-cascade models of the cochlea are practical, and may someday enable improved hearing aids, speech recognition, sound coding, and other hearing-machine applications.