Hearing aid users experience great difficulty in understanding speech in noisyenvironments. This has led to the introduction of noise reduction algorithms in hearingaids. The development of these algorithms is typically done monaurally. However, thehuman auditory system is a binaural system, which compares and combines the signalsreceived by both ears to perceive a sound source as a single entity in space. Providingtwo monaural, independently operating, noise reduction systems, i.e. a bilateralconfiguration, to the hearing aid user may disrupt binaural information, needed to localizesound sources correctly and to improve speech perception in noise.We first examine the influence of commercially available, bilateral, noise reductionalgorithms on binaural hearing. Extensive objective and perceptual evaluations withnormal hearing and hearing impaired subjects show that the bilateral adaptive directionalmicrophone (ADM) and the bilateral fixed directional microphone, two of the mostcommonly used noise reduction algorithms in hearing aids, can significantly distort thebinaural properties of the sound signals.As a second step, binaural noise reduction schemes based on a multichannel Wiener filter(MWF) approach are developed and evaluated. It is observed that a binaural hearing aiddesign significantly increases noise reduction performance owing to the larger number ofmicrophones used. Moreover, the binaural MWF and the binaural MWF with partialnoise estimation (MWF-N) provide a better combination of noise reduction performanceand preservation of binaural cues (localization performance in the horizontal hemisphere)compared to the bilateral ADM algorithm.
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