Evaluation of an adaptive beamforming method for hearing aids

Abstract

In this paper evaluations of a two‐microphone adaptive beamforming system for hearing aids are presented. The system, based on the constrained adaptive beamformer described by Griffiths and Jim [IEEE Trans. Antennas Propag. A P ‐ 3 0, 27–34 (1982)], adapts to preserve target signals from straight ahead and to minimize jammer signals arriving from other directions. Modifications of the basic Griffiths–Jim algorithm are proposed to alleviate problems of target cancellation and misadjustment that arise in the presence of strong target signals. The evaluations employ both computer simulations and a real‐time hardware implementation and are restricted to the case of a single jammer. Performance is measured by the spectrally weighted gain in the target‐to‐jammer ratio in the steady state. Results show that in environments with relatively little reverberation: (1) the modifications allow good performance even with misaligned arrays and high input target‐to‐jammer ratios; and (2) performance is better with a broadside array with 7‐cm spacing between microphones than with a 26‐cm broadside or a 7‐cm endfire configuration. Performance degrades in reverberant environments; at the critical distance of a room, improvement with a practical system is limited to a few dB.