Binaural beam-forming with dominant cue preservation for hearing aids

Abstract

For people with hearing impairment, it is important to have good speech intelligibility, while also being able to localise the sound sources. Many beam-forming algorithms for hearing aids have been proposed, that minimise the noise, in combination with spatial scene preservation of the target and the interferers. By constraining the spatial cues, the limited degrees of freedom available for the design of the filter are expended, and this, to some extent degrades the noise reduction performance. Most of these methods try to preserve both the interaural time difference (ITD) and the interaural level difference (ILD) cues of the noise components over the entire frequency spectrum. However not all frequencies rely on both the ITDs and the ILDs for the localisation of sound. More specifically, the ITDs are dominant cues in the frequencies below 1.5 kHz and the ILDs are dominant cues in the frequencies above 1.5 kHz. Based on these facts, in this thesis we try to preserve only the ILD cues of the noise components at frequencies above 1.5 kHz, while keeping the target signal undistorted. We investigate whether doing so saves the degrees of freedom that can be used to improve the noise reduction performance, in contrast to preserving both the cues. The thesis proposes two methods to preserve only the ILD cues of the interferers. The first method preserves the ILD cues perfectly, while the second method achieves a relaxed preservation of the ILD cues. Both methods show similar performance in anechoic and reverberant environments, and show that the noise reduction performance improves only mildly, when only the ILD cues of the noise components in the higher frequencies are preserved.