Guo, Meng

English

Acoustic feedback problems occur when the output loudspeaker signal of an audio systemis partly returned to the input microphone via an acoustic coupling through the air. Thisproblem often causes significant performance degradations in applications such as publicaddress systems and hearing aids. In the worst case, the audio system becomes unstableand howling occurs.In this work, first we analyze a general multiple microphone audio processing system,where a cancellation system using adaptive filters is used to cancel the effect ofacoustic feedback. We introduce and derive an accurate approximation of a frequencydomain measure—the power transfer function—and show how it can be used to predictthe convergence rate, system stability bound, and the steady-state behavior of the entirecancellation system across time and frequency without knowing the true acousticfeedback paths. This power transfer function method is also applicable to an acousticecho cancellation system with a similar structure.Furthermore, we consider the biased estimation problem, which is one of the mostchallenging problems for state-of-the-art acoustic feedback cancellation systems. A commonlyknown approach to deal with the biased estimation problem is adding a probenoise signal to the loudspeaker signal and base the estimation on that. This approachis particularly promising, since it can be shown that, in theory, the biased estimationproblem can be completely eliminated. However, we analyze a traditional probe noiseapproach and conclude that it can not work in most acoustic feedback cancellationsystems in practice, due to the very low convergence rate of the adaptive cancellationsystem when using low level and inaudible probe noise signals.We propose a novel probe noise approach to solve the biased estimation problem inacoustic feedback cancellation for hearing aids. It utilizes a probe noise signal whichis generated with a specific characteristic so that it can facilitate an unbiased adaptivefilter estimation with fast tracking of feedback path variations/changes despite its lowsignal level. We show in a hearing aid application that whereas the traditional and stateof-the-art acoustic feedback cancellation systems fail with significant sound distortionsand howling as consequences, the new probe noise approach is able to remove feedbackartifacts caused by the feedback path change in no more than a few hundred milliseconds.<br/

Analysis, Design, and Evaluation of Acoustic Feedback Cancellation Systems for Hearing Aids:- A Novel Approach to Unbiased Feedback Cancellation

https://vbn.aau.dk/ws/files/316411272/PhD_Thesis_Meng_Guo.pdf

Analysis, Design, and Evaluation of Acoustic Feedback Cancellation Systems for Hearing Aids:- A Novel Approach to Unbiased Feedback Cancellation

Abstract

Similar works

Full text

Available Versions

VBN