Adaptive Feedback Cancellation Research Articles

Acoustic feedback reduction in hearing aids—A feasibility study

Acoustic feedback in hearing aids occurs when the receiver of the hearing aid produces an acoustic signal that leaks to the microphone and causes oscillations and instability, limiting the hearing aid gain. The problem is worse in vented hearing aids, which are commonly used to reduce the unnatural feeling caused by the ear occlusion. Common solutions to the feedback problem are low-pass filtering for analog hearing aids, and adaptive feedback cancellation for digital hearing aids. Hearing aids are commonly designed primarily to compensate for the hearing loss, and therefore often suffer from feedback instability. In this work it is shown that the hearing aid can perform better if both the feedback problem and the required compensation are considered in the hearing aid design. An experiment was performed to study the hearing aid feedback mechanism in both an ear simulator and in human ears under various conditions. Then hearing aid filters that minimize the feedback problem for the human-ear data, while providing maximum gain for hearing loss compensation, were computed. The filter design problem was formulated as a convex optimization problem and solved using sequential quadratic programming. Results of the feedback path measurements and the hearing aid filters will be presented.

Reducing acoustic feedback in hearing aids

Five techniques for reducing acoustic feedback in hearing aids were investigated: an adaptive notch filter, three previously described methods for adaptive feedback cancellation, and a novel method for feedback cancellation with adaptation during quiet intervals. Through real-time implementations, these techniques were assessed for added stable gain and sound quality. Test results showed the novel system to provide the best overall performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive feedback cancellation with frequency compression for hearing aids.

The use of an adaptive feedback canceler (AFC) for howling suppression in hearing aids seems very attractive since it is not only unaffected by the changes in the operating environment, but it also limits signal degradation due to the feedback signal. This, however, requires a reference signal which is correlated with the feedback signal but not with the input signal. In hearing aids, such a signal is hard to obtain. The output signal could be used as reference if its correlation with the input signal could sufficiently be removed. If the reference signal is correlated with the input signal, the input signal will also be canceled by the AFC. Here, the use of a frequency compressor as a decorrelator is proposed. The performance of this system is then investigated via digital simulation. Results indicated that with the use of the proposed system and the proper choice of system parameters, an increase of about 18 dB in the howling margin could be achieved with minimal deterioration in output signal quality.

Active sound attenuation system with on‐line adaptive feedback cancellation

First Page