A Relative-Transfer-Function-based Post-Filter for Speech Enhancement in Hearing Aids using a Nearby External Microphone

This paper presents a novel approach for post-filtering the output of a hearing aid (HA) beamformer (BF) using an external microphone (Emic) signal where the Emic is placed in front of the HA user. The proposed approach first estimates the target relative transfer function (RTF) between the Emic and the hearing aids. The target RTF is then used for target and noise signal estimation. The estimated target and noise powers are then used to enhance the output of the HA-BF via a Wiener-like post-filter. Objective measures and subjective testing are used to evaluate the performance of the proposed post-filter (PF) with respect to the state-of-the-art single-channel noise reduction and previously proposed Emic-based post-filter designs. These evaluations show that the RTF-based approach for post-filtering the binaural HA BF outperforms previous approaches for noise reduction using an Emic and ultimately supports the use of an Emic for signal enhancement in hearing aids.