Subband Adaptive Feedback Control in Hearing Aids with Increased User Comfort

This report describes important physiological and anatomical aspects of human hearing, including instruments for hearing improvements, i.e. hearing aids. One common problem with hearing aids is acoustic feedback (howling). A new subband Adaptive Feedback Control (AFC) system for hearing aids is proposed. This system detects howling by calculating distances between zero crossings in the subband input signal. A stable subband zero crossing distance measure indicates that howling is present in a particular subband. This triggers an adaptation to estimate and attenuate the feedback channel. The adaptation is driven by a probe noise sequence constrained in both time and frequency. This constraint implies increased signal quality and that user discomfort due to emitted probe noise is reduced. Also, an effective and reliable adaptation is achieved. The method has proven to operate well in computer simulations, with speech as well as music as signal input. Initial simulations indicate that an increased hearing aid gain of at least 15 dB is possible.