Abstract:
Environmental noises such as cocktail party babble, traffic, and restaurant clatter are a continuing source of irritation to hearing aid wearers. One approach to reducing this noise is to provide the wearer with a directional field of hearing. Sounds coming from the back and sides are attenuated, while sounds coming from the front, or look direction, are unattenuated. Several approaches to designing such systems have been attempted: directional microphones, passive microphone arrays, and classical adaptive filter microphone array beamformers. These techniques are compromised by poor performance in reverberant environments, undesirable packaging constraints, and large computational requirements. This paper describes an efficient algorithm for a two-microphone directional hearing system based on time-varying frequency-domain Wiener filtering. The frequency-dependent SNR estimates necessary to determine the time-varying frequency-dependent attenuation of the Wiener filter are based on interaural time-of-arrival and interaural magnitude differences. Two alternative formulas are presented for calculating these SNR estimates. A study is made of the frequency resolution requirements needed to achieve good results using the Wiener filtering approach. Results from clinical trials showing improvements in both objective intelligibility scores and subjective SRT scores are presented.