Acoustic Feedback Cancellation for Hearing Aids Using a Fixed RTF-Constrained Null-Steering Beamformer

Recently it has been proposed to use a fixed beamformer to cancel the acoustic feedback for a custom earpiece with multiple integrated microphones and loudspeakers. By steering a spatial null in the direction of the hearing aid loudspeaker theoretically perfect feedback cancellation can be achieved. In contrast to previous approaches that constrained the beamformer coefficients in a reference microphone to a simple delay, in this paper we use a constraint based on the relative transfer function of the incoming signal aiming to perfectly preserve the incoming signal. Experimental results using measured acoustic feedback paths from a custom earpiece with three microphones show that the proposed RTF constrained null- steering beamformer allows to substantially increase the added stable gain even for unknown acoustic feedback paths, e.g., with a telephone receiver close to the ear. Furthermore, it yields a high perceptual speech quality of the incoming signal even for unknown incoming signal directions.