An auditory model for intelligibility and quality predictions

Abstract

The perceptual effects of audio processing in devices such as hearing aids can be predicted by comparing auditory model outputs for the processed signal to the model outputs for a clean reference signal. This paper presents an improved auditory model that can be used for both intelligibility and quality predictions. The model starts with a middle-ear filter, followed by a gammatone auditory filter bank. Two-tone suppression is provided by setting the bandwidth of the control filters wider than that of the associated analysis filters. The analysis filter bandwidths are increased in response to increasing signal intensity, and compensation is provided for the variation in group delay across the auditory filter bank. Temporal alignment is also built into the model to facilitate the comparison of the unprocessed reference with the hearing-aid processed signals. The amplitude of the analysis filter outputs is modified by outer hair-cell dynamic-range compression and inner-hair cell firing-rate adaptation. Hearing loss is incorporated into the model as a shift in auditory threshold, an increase in the analysis filter bandwidths, and a reduction in the dynamic-range compression ratio. The model outputs include both the signal envelope and scaled basilar-membrane vibration in each auditory filter band.