In set-top videoconferencing, the complete videoconferencing system fits unobtrusively on top of the television. The microphone sound pickup system is one of the most important functional blocks with constraints of small size, high performance, and low cost. Persons speaking several feet away from the system must be picked up satisfactorily while noise generated internally in the system by the cooling fan and hard drive, and noise generated externally from air conditioning and nearby computers must be attenuated. In this paper, a three microphone superdirective array is described which meets these constraints. An analog highpass and lowpass filter are used to merge two of the microphone signals to form a single channel, so that a single stereo A/D converter is required to process the three microphone signals. The microphone signals are then linearly combined so as to maximize the signal-to-noise ratio, resulting in nulls steered toward nearby objectionable noise sources.
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