PhD Thesis Defence

Multi-Microphone Noise Reduction for Hearing Assistive Devices

Andreas Koutrouvelis

The paramount importance of good hearing in everyday life has driven an exploration into the improvement of hearing capabilities of (hearing impaired) people in acoustic challenging situations using hearing assistive devices (HADs). HADs are small portable devices, which primarily aim at improving the intelligibility of an acoustic source that has drawn the attention of the HAD user. One of the most important steps to achieve this is via filtering the sound recorded using the HAD microphones, such that ideally all unwanted acoustic sources in the acoustic scene are suppressed, while the target source is maintained undistorted. Modern HAD systems often consist of two collaborative (typically wirelessly connected) HADs, each placed on a different ear. These HAD systems are commonly referred to as binaural HAD systems. The noise reduction filters designed for binaural HAD systems are referred to as binaural beamformers.

Binaural beamformers typically change the magnitude and phase relations of the microphone signals by forming a beam towards the target's direction while ideally suppressing all other directions. This may alter the spatial impression of the acoustic scene, as the filtered sources now reach both ears with possibly different relative phase and magnitude differences compared to before processing. This will appear unnatural to the HAD user. Therefore, there is an increasing interest in the preservation of the spatial information (also referred to as binaural cues) of the acoustic scene after processing. The present dissertation is mainly concerned with this particular problem and proposes several alternative binaural beamformers which try to exploit the available degrees of freedom to achieve optimal performance in both noise reduction and binaural-cue preservation.

Additional information ...

Overview of PhD Thesis Defence