Acoustic Feedback Cancellation Techniques for Hearing Aid Applications in Noisy Environments

摘要

Acoustic feedback cancellation is a problem of great interest to researchers in Hearing Aid Device (HAD) applications. Acoustic feedback effect arises due to the acoustic leakage from the loudspeaker to the input microphone. It interferes with and degrades the receiving speech/sound signals to the HADs. It is inadvertently picked up by the HAD microphone and re-amplified which can lead to the appearance of undesirable irritating "whistling" and "screeching" sounds, often referred to as howling effect. Adaptive Feedback Cancellation (AFC) techniques are widely used to eliminate the undesired acoustic feedback effect arising in the HADs due to the coupling between the speaker and the microphone of the HAD. However, the closed loop formed by the acoustic feedback path makes the spectrally colored desired speech signal highly correlated with the feedback signal leading to biased feedback path estimate. Thus, for efficient feedback cancellation, decorrelating techniques are utilized with AFC methods. This thesis proposes two novel methods which involve prefiltering and noise injection as decorrelating techniques to eliminate the acoustic feedback effect in the HADs in presence of noisy environment. These methods involve utilization of a computationally efficient Spectral Flux feature-based voice activity detector which supervises the feedback cancellation process. The proposed algorithm's performance is objectively evaluated for realistic noisy conditions. The simulations performed for the proposed methods support the effectiveness and better performance of the proposed algorithms for the HAD applications over several earlier methods. In this work, we also propose a novel low latency smartphone-based application that demonstrates the real-time operation (i.e. frame by frame operation of input data) to cancel the negative effects of acoustic feedback. With the proposed application, we can estimate the transfer function between speaker and microphone of the smartphone in the changing room acoustics making the feedback cancellation very effective.