ASA 127th Meeting M.I.T. 1994 June 6-10

5aPP3. Multimicrophone hearing aids with binaural output.

Joseph G. Desloge

Patrick M. Zurek

William M. Rabinowitz

Res. Lab. of Electron., Rm. 36-797, MIT, 77 Massachusetts Ave., Cambridge, MA 02139

Multimicrophone hearing aids, implemented with fixed (time-invariant) filters, can enhance hearing aid sensitivity in a target direction (e.g., straight ahead) relative to other directions. Most designs, however, produce a monaural output, resulting in the loss of interaural signal differences that provide a sense of space. This paper explores single- and dual-array binaural output hearing aids designed to achieve a compromise between directionality and the fidelity of interaural time differences (ITDs). Single-array systems use one broadside array to form both output signals; microphone weights are selected to maximize the directional sensitivity for each output signal, subject to a constraint on the error between the system's output ITDs and the ``true'' ITDs. A special case of these systems exploits the facts that low-frequency ITDs dominate sound localization and that broadside arrays achieve significant directionality only at high frequencies. In this case, the microphone weights retain ``true'' ITDs at low frequencies and maximize directionality at high frequencies. Dual-array systems use two independent endfire arrays to generate the two output signals; microphone weights are selected to maximize directionality for each array separately, and the physical spacing between the arrays produces the ITDs between the two output signals. [Work supported by NIDCD.]