MICROPHONE-ARRAY HEARING-AIDS WITH BINAURAL OUTPUT .1. FIXED-PROCESSING SYSTEMS

This work is aimed at developing a design for the use of a microphone array with binaural hearing aids, The goal of such a hearing aid is to provide both the spatial-filtering benefits of the array and the natu ral benefits to sound localization and speech intelligibility that acc rue from binaural listening, The present study examines two types of d esigns for fixed-processing systems: one in which independent arrays p rovide outputs to the two ears, and another in which the binaural outp uts are derived from a single array, For the latter, various methods a re used to merge array processing with binaural listening, In one appr oach, filters are designed to satisfy a frequency-dependent trade betw een directionality and binaural cue fidelity, In another, the micropho ne signals are filtered into low-and high-frequency components with th e lowpass signals providing binaural cues and the highpass signal bein g the single output of the array processor, Acoustic and behavioral me asurements were made in an anechoic chamber and in a moderately reverb erant room to evaluate example systems, Theoretical performance was ca lculated for model arrays mounted on an idealized spherical head, Resu lts show that both single-and dual-array systems provided target-intel ligibility enhancements (2-4 dB improvements in speech reception thres hold) relative to binaural cardioid microphones, In addition, the bina ural-output systems provided cues that assist in sound localization, w ith resulting performance depending directly upon the cue fidelity, Fi nally, the sphere-based calculations accurately reflected the major fe atures of the actual head-mounted array results, both in terms of dire ctional sensitivity and output binaural cues.