Microphone system for teleconferencing system

DETAILED DESCRIPTION In one aspect, the invention generally features a microphone system for use in an environment where an acoustic source emits energy from diverse and varying locations within the environment.
The microphone system has at least two directional microphones, mixing circuitry, and control circuitry.
The microphones are held each directed out from a center point.
The mixing circuitry combines the electrical signals from the microphones in varying proportions to form a composite signal, the composite signal including contributions from at least two of the microphones.
The control circuitry analyzes the electrical signals to determine an angular orientation of the acoustic signal relative to the central point, and substantially continuously adjusts the proportions in response to the determined orientation and provides the adjusted proportions to the mixing circuitry.
The values of the proportions are selected so that the composite signal simulates a signal that would be generated by a single directional microphone pivoted about the central point to direct its maximum response at the acoustic signal as the acoustic signal moves about the environment.
Particular embodiments of the invention can include the following features.
The multiple microphones are mounted in a small, unobtrusive, centrally-located "puck" to pick up the speech of people sitting around a large table.
The puck may mount two dipole microphones or four cardioid microphones oriented at 90.
degree.
from each other.
The pivoting and directing are to discrete angles about the central point.
The mixing circuitry combines the signals from the microphones by selectively adding, subtracting, or passing the signals to simulate four dipole microphones at 45.
degree.
from each other.
The mixing proportions are specified by combining and weighting coefficients that maintain the response of the virtual microphone at a nearly uniform level.
At least two of the adjusted coefficients are neither zero nor one.
The microphone system further includes echo cancellation circuitry having effect varying with the selected proportions and virtual microphone direction, the echo cancellation circuitry obtaining information from the control circuitry to determine the effect