Spectral enhancement to compensate for reduced frequency selectivity

Abstract

A new method of spectral enhancement has been developed to compensate for reduced frequency selectivity in people with sensorineural hearing impairment. The goal is to modify a sound such that it evokes as nearly as possible the same excitation patterns in an ear with reduced frequency selectivity as would be evoked by the unmodified sound in a normal ear. Processing is performed in the spectral domain, using an overlap-add procedure. Enhanced spectra are calculated using a nonnegative-least-squares algorithm for matching excitation patterns. When compensating for a moderate degree of auditory-fiber broadening, this procedure dramatically increases spectral contrast while preserving relatively normal sound quality. To examine the effects of enhancement on the intelligibility of speech in speech-shaped noise (at −3 dB SNR), a pilot experiment was performed with normal-hearing subjects, using a spectral smearing method [T. Baer and B. C. J. Moore, J. Acoust. Soc. Am. 94, 1229–1241 (1993)] to simulate some aspects of reduced frequency selectivity. Results show that the enhancement compensates partially for the effects of spectral smearing and should thus improve the intelligibilty of speech in noise for the hearing-impaired. Experiments are presently underway to test the effects of enhancement on speech perception with hearing-impaired subjects. [Work supported by the MRC.]