Strategy-selective noise reduction for binaural digital hearing aids

• Authors: Thomas Wittkop;Volker Hohmann
• Venue: Speech Communication - Special issue on speech processing for hearing aids
• Year: 2003

In this paper, different binaural signal processing strategies for noise reduction are derived and assessed which are based on particular assumptions on the (spatial) properties of the target signal and the undesired interfering signals. The processing strategies are evaluated with respect to their technical performance using artificial signals. They are shown to function if the underlying assumptions are met. The processing strategies are combined within a single, strategy-selective algorithm which automatically selects appropriate processing strategies depending on the acoustical situation. For this, a measure for the general diffusiveness or coherence, respectively, of the sound field is employed to classify the situation and to switch off particular processing strategies if necessary. Time constants were optimized with respect to the sound quality by subjective preference measurements. The algorithm was then assessed by measurements with eight hearing-impaired subjects who exhibit two different types of hearing loss (high frequency hearing loss and flat hearing loss). The subjective preference as well as speech reception thresholds (SRTs) in noise are measured under realistic free-field conditions in a laboratory environment. No significant improvement of the SRT was found on average. However, the results also suggest that there might be an improvement of speech intelligibility for subjects with a flat hearing loss in the free-field (dichotic) listening situation with interfering speech signals or diffuse cafeteria noise. Furthermore, the results of the subjective assessment exhibit a higher quality of the processed signal than the unprocessed signal especially in the diffuse cafeteria noise situation.