  This work 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 concomitantly minimizes a nonlinear function of
the difference between input and output IPD, which is strictly related to ITD,
and preserves the natural coherence of the directional noise captured by the
reference microphones. Objective measures and psychoacoustic experiments
corroborate the theoretical findings, showing 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
the MWF-IC as a noise reduction technique that provides resid-ual noise spatial
preservation for both diffuse and directional noise sources in frequencies
below 1.5 kHz.
