A Noise Reduction Postfilter for Binaurally Linked Single-Microphone Hearing Aids Utilizing a Nearby External Microphone

The use of a nearby external microphone for addressing front-back ambiguity in single-microphone hearing aid devices is investigated. Strategic placement of the external microphone is able to provide benefits from the body shielding back-directional noise and therefore information for discriminating between the frontal and back hemispheres. The scattering effects of the body are first analyzed to yield a placement strategy of the external microphone for maximizing the shielding effect of the body against back-directional noise sources while also optimizing for speech intelligibility. Assuming optimal placement, a frontal target source presence probability (FTSPP) estimator is derived. Using the FTSPP estimator, a more comprehensive noise estimator is proposed, which considers both stationary and nonstationary interferers. The performance of the proposed noise estimator is evaluated in its application for postfiltering the output of a binaural beamformer. The effect of postfiltering using the proposed noise estimator is to provide further reduction of directional noise from the lateral and back direction while preserving the frontal target signal. The resulting enhancement with the proposed noise estimator provides a better signal-to-noise ratio and improved objective speech quality and intelligibility of a frontal target speaker compared to the state of the art.