Abstract
AMNOR is a new type of noise-reduction microphone system which uses a microphone arrayand digital signal processing. In this paper, the theory of AMNOR is described in the frequency domain, and its directivity characteristics are studied. Then, it is shown that, under some simple noise conditions, AMNOR forms the same directivity patterns as those formed by conventional directional microphones. In contrast to the directivity characteristics of conventional directional microphones which are assumed to be optimal for some restricted noise environments, AMNOR can realize the optimal directivity characteristics adaptively for a wide variety of existing noise environments. This is accomplished in AMNOR by the following three functions;(1) AMNOR forms M-1 (where M is the number of microphone elements) dead angles with respect to the noise arrival directions, (2) AMNOR optimizes the directivity lobe figure (3) AMNOR performs directivity control of (1) and (2) for each frequency band independently.
