A New Methodology based on Pulse Compression Technique for Hearing Aids Distortion Measurement

Hearing aids are the most widespread devices for treating hearing loss, especially among older adults. However, the performance of these devices is reduced by harmonic distortion and intermodulation distortion due to nonlinearities in the amplifying system. It is therefore important to have a quantitative measure of the nonlinear behavior of these devices. Several estimators of the degree of distortion introduced by hearing aids have been defined and standardized. In parallel with the definition of distortion measures, effective techniques for modeling nonlinear structures and identifying the corresponding model parameters have been developed. This paper moves in this context and proposes a new methodology for estimating distortions in hearing aids: it is shown how, by focusing the processing effort on model identification, from the identified structure it is possible to obtain the different estimators terms defined by the relevant standards, in order to provide a quantitative assessment of the nonlinear effect of structure on signals. Distortion estimation results are obtained by using a Hammerstein model for representing the nonlinear system; these results are compared with those obtained by applying the standard procedure based on IEC 60118. The results obtained in terms of harmonic distortion and intermodulation distortion show the effectiveness of the proposed method in comparison with the methodology recommended by regulatory standards, providing very similar results in terms of estimation, but also being more efficient, as the use of Exponential Swept-Sine signals avoids the need for an iterative approach and allows the different estimators defined in the regulations to be obtained from a single model identification procedure.