Estimating Direction of Arrival From Plural Microphones

Abstract

A noise suppression system includes plural microphones, a fixed beam former, a blocking matrix, plural adaptive filters, and a direction of arrival circuit coupled to the adaptive filters that prevents the filters from adapting in the presence of a signal in the look direction. The direction of arrival circuit causes the filters to adapt more quickly in the absence of a signal in the look direction. A pair of adjustable gain circuits is coupled to each microphone. A first adjustable gain circuit from each pair is calibrated during the presence of a desired signal and a second adjustable gain circuit from each pair is calibrated during the presence of an interfering signal. A fixed null-forming circuit is coupled to a first pair of variable gain circuits and an adaptive null forming circuit is coupled to a second pair of adjustable gain circuits. The ratio of the gains of the null forming circuits is used as a control signal. Successive ratios are averaged with a variable smoothing constant and a control signal is derived from the averaged ratios.

What is claimed as the invention is: 
     
         1 . A noise suppression circuit comprising:
 a first microphone;   a second microphone;   a fixed beam former coupled to the first microphone and to the second microphone;   a blocking matrix coupled to the first microphone and to the second microphone;   adaptive filters coupled to the blocking matrix;   a subtraction circuit coupled to the output of the fixed beam former and to the outputs of the adaptive filters;   a direction of arrival circuit, coupled to said first microphone, said second microphone, and said adaptive filter, that prevents the adaptive filter from adapting in the presence of a signal in the look direction of the direction of arrival circuit.