Perceptually Relevant Preservation of Interaural Time Differences in Binaural Hearing Aids

This paper presents a noise reduction method with perceptually relevant preservation of the interaural time difference (ITD) of the residual noise in binaural hearing aids. The interaural coherence (IC) concept, previously applied to the multichannel Wiener filter (MWF) for preservation of the spatial subjective sensation of diffuse noise fields, is proposed here to both preserve and emphasize the ITD binaural cues of a directional acoustic noise source. It is demonstrated that the previously developed MWF-ITD technique may decrease the original IC magnitude of the processed noise, consequently increasing the variance of the interaural phase difference (IPD) of the output signals. It is shown that the MWF-IC technique simultaneously minimizes a nonlinear function of the difference between input and output IPD, which is strictly related to ITD, and preserves the natural coherence of directional noise captured by the reference microphones. Objective measures and psychoacoustic experiments corroborate the theoretical findings, showing that the MWF-IC technique provides relevant noise reduction, while preserving the original ITD subjective perception and original lateralization for a directional noise source. These results are especially relevant for hearing aid designers, since they indicate MWF-IC as a noise reduction technique that provides residual noise spatial preservation for both diffuse and directional noise sources in frequencies below 1.5 kHz.