Electronic cancellation of acoustic feedback to increase hearing-aid stability

Abstract

The acoustic feedback which causes a hearing aid to become unstable at high gains is effectively reduced by the addition of negative electrical feedback. Electrical feedback is formed by a system estimator which closely matches the open-loop transfer function of an in situ hearing aid. The system estimator is produced by correlating the estimator signal with the hearing-aid signal. Because the estimator does not affect the characteristics of the hearing aid, speech intelligibility is not degraded by this feedback suppression circuit as it is by most other schemes. Thus 10 to 15 dB of additional stable gain have been achieved through the use of stabilizing negative electrical feedback.