INSTITUTE OF PHYSICS PUBLISHING PHYSIOLOGICAL MEASUREMENT.pdf

INSTITUTE OF PHYSICS PUBLISHING PHYSIOLOGICAL MEASUREMENT Physiol. Meas. 25 (2004) 945–956 PII: S0967-3334(04)76307-8 Physiological assessment of contrast-enhancing frequency shaping and multiband compression in hearing aids Ian C Bruce Department of Electrical and Computer Engineering, McMaster University, Hamilton, Ontario L8S 4K1, Canada E-mail: ibruce@ieee.org Received 13 February 2004, accepted for publication 8 April 2004 Published 22 July 2004 Online at stacks.iop.org/PM/25/945 doi:10.1088/0967-3334/25/4/013 Abstract Spectral enhancement is now being used in many hearing aids in an attempt to compensate for broadened cochlear filtering. However, spectral enhancement may be counteracted by multiband-compression algorithms designed to compensate for the reduced dynamic range of the impaired cochlea. An alternative scheme for spectral enhancement, contrast-enhancing frequency shaping (CEFS), has been proposed, which results in an improved neural representation of the first and second formants of voiced speech segments in the impaired ear. In this paper, models of the normal and impaired ear are used to assess the compatibility of CEFS with multiband compression. Model auditory nerve responses were assessed under four conditions: (1) unmodified speech presented to a normal ear; (2) amplified, unshaped speech presented to an impaired ear; (3) CEFS speech presented to an impaired ear; and (4) CEFS+multiband-compression speech presented to an impaired ear. The results show that multiband compression does not reduce the benefits of CEFS, and in some cases multiband compression assists in preventing distortion of the neural representation of formants. These results indicate that the combination of contrast-enhancing frequency shaping and multiband compression should lead to improved perception of voiced speech segments in hearing aid users. Keywords: spectral enhancement, multiband compression, hearing aids, auditory nerve model, hearing loss, formant representation 0