Hearing aid measurements with speech and noise signals

An increasing number of hearing aid types include one or more features which are intentionally non-linear. In such devices measurement of frequency response and distortion using sweep tone measurements are typically of little relevance. Five different non-linear hearing aid types were used to evaluate three different broad-band measuring methods. The results revealed that these methods were meaningful in estimating average frequency response obtained with a specific input signal, but none of the three methods used in the study was able to evaluate separately the effects of the most important signal modifications: memoryless non-linearity like peak clipping, time-varying gain from AGC and additive internal noise.