Hearing aid having compensation for acoustic feedback.

摘要

A hearing aid (figs. 1,3) includes a filter (27) in an electrical feedback path (k-m), the characteristics of which filter (27) are calculated to model acoustic coupling between the receiver (11) and microphone (5) of the aid. A limiter (15) is inserted in the main electrical pathway (b-c-d-e-f-g) between the microphone (5) and the receiver (11) to provide stability in the presence of sudden sound bursts. A noise signal (N) is injected continuously into the electrical circuit and is used to adapt the characteristics of the filter (27) to accommodate changes in the acoustic coupling. The level of the noise signal (N) can be varied to match changes in residual signal level to maintain signal to noise ratio and to optimise the rate of adaption commensurate with satisfactory hearing function whilst the noise itself is unobtrusive to the user.