Measuring and predicting the quality of nonlinearly distorted music and speech as perceived by hearing-impaired people.

Abstract

The goals of this study were to characterize and model the perception of nonlinearly distorted speech and music by hearing-impaired listeners. Hearing-impaired listeners were asked to rate the perceived quality of speech and music that had been subjected to various forms of nonlinear distortion, some of which are inherent to certain hearing aid designs including (1) hard and soft, symmetrical and asymmetrical clipping; (2) center clipping; (3) “full-range” distortion, produced by raising the absolute magnitude of the instantaneous amplitude of the signal to a power (8800;1), while preserving the signal of the amplitude; (4) automatic gain control (AGC); (5) output limiting. Stimuli were subjected to frequency-dependent amplification as prescribed by the “Cambridge formula” before presentation via Sennheiser HD580 earphones. The pattern of the rating was reasonably consistent across subjects with only two of ten subjects not making consistent ratings. The mean ratings were not lower with increasing amount of soft or center clipping or when the compression ratios of the AGC and output limiting were increased. The deleterious effects produced by these nonlinear distortions may have been offset by the beneficial effects of improving audibility and compensating for loudness recruitment. [Work supported by Deafness Research Foundation.]