Proceedings of the NAG-DAGA International Conference on Acoustics pages:5-8
NAG-DAGA International Conference on Acoustics location:Rotterdam date:23-26 march 2009
Hearing aid users experience great difficulty in understanding speech in noisy
environments. This has led to the introduction of noise reduction algorithms in hearing
aids. The development of these algorithms is typically done monaurally. However, the
human auditory system is a binaural system, which compares and combines the signals
received by both ears to perceive a sound source as a single entity in space. Providing
two monaural, independently operating, noise reduction systems, i.e. a bilateral
configuration, to the hearing aid user may disrupt binaural information, needed to localize
sound sources correctly and to improve speech perception in noise.
We first examine the influence of commercially available, bilateral, noise reduction
algorithms on binaural hearing. Extensive objective and perceptual evaluations with
normal hearing and hearing impaired subjects show that the bilateral adaptive directional
microphone (ADM) and the bilateral fixed directional microphone, two of the most
commonly used noise reduction algorithms in hearing aids, can significantly distort the
binaural 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 aid
design significantly increases noise reduction performance owing to the larger number of
microphones used. Moreover, the binaural MWF and the binaural MWF with partial
noise estimation (MWF-N) provide a better combination of noise reduction performance
and preservation of binaural cues (localization performance in the horizontal hemisphere)
compared to the bilateral ADM algorithm.