Perception of nonlinear distortion by hearing-impaired people

All hearing aids and communication devices introduce nonlinear distortion. The perception of distortion by hearing-impaired subjects was studied using artificial controlled distortions of various amounts and types. Subjects were asked to rate the perceived quality of distorted speech and music. Stimuli were subjected to frequency-dependent amplification as prescribed by the 'Cambridge formula' before presentation via Sennheiser HD580 earphones. The pattern of the ratings was reasonably consistent across subjects, but two of the eight subjects showed inconsistent results for the speech stimuli. Center clipping and soft clipping had only small effects on the ratings, while hard clipping and 'full-range' distortion had large effects. The results indicate that most hearing-impaired subjects are able to make orderly and consistent ratings of degradations in sound quality introduced by nonlinear distortion. The pattern of results could be predicted reasonably well using a model developed to account for the perception of distortion by normally hearing subjects.