On transient distortion in hearing aids with volume compression

The influence of harmonic distortion on the performance of ordinary hearing aids is discussed, as well as several kinds of possible distortions found in the transient state when compression is introduced. Transient response was determined for several hearing aids with compression that are available on the market. It is shown that each transient response is composed of two parts: the first part is determined by the frequency response of the whole transmission channel; the second one by the transient response of compression. The latter may cause overshoots, during which large distortions are found in some hearing aids. In others, a superposition of, or a modulation by, the damped low-frequency oscillation was observed at the output. Examples of such distortion are presented.