Experimental evaluation of speech enhancement methods in remote microphone systems for hearing aids

Enhancing speech intelligibility for hearing-impaired subjects in complex acoustic conditions is still a challenging topic of research. To mitigate the detrimental effects of background noise and reverberation, current hearing instruments incorporate various hardware and software strategies, among which speech enhancement algorithms are of primary importance. In this paper, two algorithms based on the multichannel Wiener filter (previously reported in the literature) and one proprietary algorithm are experimentally assessed and compared. All of them make use of a remote microphone worn by the speaker of interest. The objective of these algorithms is to improve the speech contribution within the hearing aid microphone signals. The algorithms are assessed in terms of interference reduction performance, speech quality, spatial hearing preservation, and technical requirements. Using a recorded database of audio signals, the effects of the signal-to-noise ratio and of the delay between the remote and hearing aid microphone signals are studied. The results show that the proprietary algorithm provides a good performance and yields the lowest distortion of the binaural localization cues, while being the most efficient in terms of computational cost and wireless usage. The main drawback is the degradation of the output sound quality that is observed when the remote and hearing aid microphone signals are not temporally aligned.

Auditory externalization of a remote microphone signal

Vincent Pierre Olivier Grimaldi

A remote microphone (RM) system can be used in combination with wearable binaural communication devices, such as hearing aids (HAs), to improve speech intelligibility. Typically, a speaker is equipped with a body-worn microphone which enables to pick up their voice with a high signal-to-noise ratio (SNR). However, if this signal is played diotically through the receivers (i.e. the same signal in both ears), the necessary cues enabling the auditory system to locate the sound source are bypassed. This can affect the ability of the listener to feel immersed in the environment or to follow a conversation, especially for hearing-impaired (HI) listeners. Auditory sound source localization in humans is performed by the auditory system owing to the interpretation of various cues related to the physical sound propagation from this source to the eardrums of the listener. This is mainly enabled by the binaural structure of the auditory system.Previous works have successfully developed a method to provide a simplified spatialization of the RM signal which enabled normal-hearing (NH) and HI listeners to locate sound sources in azimuth, while preserving speech intelligibility. However, the proposed method yielded common spatial hearing perceptual artefacts, such as in-head localization and front/back confusion.This thesis is devoted to the investigation and the perceptual evaluation of wearable devices-compatible audio playback solutions aiming at enhancing the realism of this spatialization. In particular, the goal is to improve the externalization of a sound source, i.e. to ensure it is perceived outside the head, and possibly at a certain distance corresponding to its physical location in the environment. For this purpose, early reflections (ERs) in a room play a key role. Hence, several signal processing approaches to provide ERs in the binaural synthesis were investigated. Subsequently, a subjective listening study was conducted, in which NH and HI aided listeners had to evaluate the perceived auditory distance with various binaural rendering strategies. The results show that the superimposition of ERs with the considered methods significantly improves the perception of auditory distance for NH and HI listeners. The study also provides insights about auditory distance perception in aided HI listeners with severe-to-profound hearing loss. A follow-up study was conducted with NH listeners and showed that a complete implementation of these strategies might improve auditory distance perception while preserving spatial awareness. In these studies, subjects had their head fixed.Previous studies have shown that head movements coupled with head-tracking can contribute to the auditory externalization of a virtual sound source. The next part of this thesis reports the development of a head-tracking algorithm compatible with wearable devices, relying solely on two 3-axis accelerometers. While showing promising results, the limitations of the developed algorithm still yield mismatches in the estimation. Consequently, a subjective listening test was conducted with NH listeners to study the effect of head-tracking artefacts on the perception of externalization and the performance in azimuth localization of a sound source. The results suggest that auditory externalization is not affected by a large latency or the amplitude mismatch. Latency did not decrease the performance in localization either, contrarily to the amplitude mismatch.

EPFL2022

Implementation of a binaural localization algorithm in hearing aids: Specifications and achievable solutions

Gilles André Courtois, Hervé Lissek, Patrick Marmaroli

This article introduces the constraints and issues related to the implementation of a binaural localization algorithm on a pair of hearing aids. The algorithm should improve the rendering of the spatial information available in the audio signals, which are usually distorted by the signal processing algorithms in the hearing devices, thus degrading localization cues. First, several reported algorithms achieving binaural sound localization in the frontal horizontal plane are reviewed. The way in which the standard methods and processes could be used within the context of hearing aids is then discussed. Finally, a solution that is suitable for a certain type of systems is proposed.

2014

Binaural hearing aids with wireless microphone systems including speaker localization and spatialization

Gilles André Courtois, Hervé Lissek, Patrick Marmaroli

The digital wireless microphone systems for hearing aids have been developed to provide a clean and intelligible speech signal to hearing-impaired listeners for e.g. school or teleconference applications. In this technology, the voice of the speaker is picked up by a body-worn microphone, wirelessly transmitted to the hearing aids and rendered in a diotic way (same signal at both ears), preventing any speaker localization clues from being provided. The reported algorithm performs a real-time binaural localization and tracking of the talker so that the clean speech signal can then be spatialized, according to its estimated position relative to the aided listener. This feature is supposed to increase comfort, sense of immersion and intelligibility for the users of such wireless microphone systems.

2015

Auditory externalization of a remote microphone signal

Vincent Pierre Olivier Grimaldi

EPFL2022