Towards a general measure of distortion.

An approach to the measurement of distortion in hearing aids is presented. Distortion is first defined in general terms. The technique is then applied to the specific problem of predicting the detectability of non-linear distortion. Distortion indices have been obtained for two common, but very different forms of distortion: peak clipping (common to most conventional hearing aids); and, quantization (a form of distortion common to digital systems including digital hearing aids). Distortion indices were derived for the two forms of distortion in steady-state vowels. The results showed good agreement between the distortion indices at the just-detectable level of distortion.