SUPPRESSION OF ACOUSTIC FEEDBACK IN HEARING AIDS USING DUAL ADAPTIVE FILTERING

Abstract

Acoustic feedback is a major problem in most of the hearing aid users. This feedback corrupts the speech signal and causes instability. In this thesis, a new solution approach for the suppression of continuous acoustic feedback in the digital hearing aids has been dealt with. In this method, two adaptive filters work in tandem to mitigate the acoustic feedback. The error signal of the first adaptive filter is used as a desired response for the second adaptive filter and the filter weights are adapted using Normalized Least Mean Square (NLMS) and modified NLMS algorithms which is a novel approach presented in this thesis. Due to the correlation between input and desired response, a bias is found in the adaptive filter‟s estimate of the feedback path. An appropriate delay is inserted at the output of the hearing aid to reduce this bias. Based on this delay based processing, a new strategy is proposed to exchange the weights between the two adaptive filters. Unlike previous techniques, initial weights of the adaptive filters are chosen other than either 1‟s or 0‟s such that faster convergence is achieved. Computer simulations are performed and the results verify the effectiveness of the proposed method.