Preserving binaural cues in noise reduction algorithms for hearing aids

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. In this research project, we first examined the influence of commercially available, bilateral, noise reduction algorithms on binaural hearing. Extensive objective and perceptual evaluations showed 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. These distortions are well within the range used by the human auditory system. In what follows, three binaural algorithms, based on a multichannel Wiener filter (MWF) approach, were developed and evaluated. hese algorithms assume a communication link between both hearing aids. It was observed that a binaural hearing aid design significantly increased noise reduction performance. Moreover, the binaural MWF, the binaural MWF with partial noise estimation (MWF-N) and the binaural MWF with interaural transfer function extension (MWF-ITF) provided a better combination of noise reduction performance and preservation of binaural cues compared to the bilateral ADM algorithm.