Spectral enhancement using a two-filter model of impaired frequency selectivity

Abstract

Neural tuning curves can be described as comprising two shapes: a narrow ‘‘tip’’ filter with high sensitivity, and a wider ‘‘tail’’ filter with lower sensitivity. When cochlear function is impaired, the sensitivity of the tip filter decreases. The tail filter characteristics are difficult to measure in normal-hearing subjects using psychophysical techniques such as the notched-noise method. However, with mild to severe cochlear hearing loss, the tail filter has a greater influence on the results, and becomes easier to measure. Auditory filter shapes were estimated using the notched-noise method over a wide range of center frequencies for subjects with differing degrees of hearing loss. These data were used to construct a model that predicts typical filter shapes as a function of frequency and hearing loss. The model is being used to improve the accuracy of a spectral contrast enhancement method intended to compensate for the effects of reduced frequency selectivity. The method is similar to one also being developed in this laboratory [T. Baer and B. C. J. Moore, this meeting], but uses a filter bank rather than overlap-add FFTs. Results of intelligibility tests using speech in speech-shaped noise, enhanced by this method and tested on hearing-impaired subjects, will be described. [Work supported by the MRC.]