Controlling the adaptation of feedback cancellation filters - problem analysis and solution approaches

Feedback is an inherent problem to all hearing aid applications. The compensation approach, i.e. modelling the feedback path with an adaptive FIR filter is a method which allows avoiding feedback without effecting the desired signal. However, this approach is hard to be realized. Due to the correlation of the input and feedback signals, the adaptation is crucial and has to be controlled sophistically. In the paper, a detailed analysis of the feedback compensator structure is given and compared to the echo cancellation structure. It will be shown that classical control methods which have proven to be powerful for echo cancellation, cannot be applied for feedback cancellation and alternative control methods will be introduced and evaluated.