Abstract: A multi-channel echo canceller comprises a set of subtractors connected respectively in communication channels for respectively receiving a signal from a respective microphone and cancelling an echo contained in it with a cancelling signal, and a set of adaptive filters associated respectively with the subtractors. Each adaptive filter has a set of vectors of filter coefficients. A time difference between propagation delays of the received signals is estimated, and a signal having the largest content of echo components is selected and applied to the adaptive filters. One of coefficient vectors is identified according to the estimated time difference and the selected signal. Each adaptive filter varies its filter coefficients of the identified vector with a correction term proportional to the output of the associated subtractor for filtering the selected signal using the coefficients of the identified vector to derive an echo replica, which is supplied to the associated subtractor as the cancelling signal.

Abstract: A balancing resistor and thermistor network for telephone circuits, and combination with an external relay, which reliably handles all three levels of adverse conditions, automatically resets under certain conditions, is physically small in size, and is strong. It is a flat ceramic substrate on both surfaces of which are screen-printed thick-film balancing resistor films. Also screen-printed on both surfaces are termination traces having portions so located that when the substrate substantially instantaneously fractures it reliably and substantially instantaneously breaks the circuits through the resistive films, the fracture occurring in response to a sudden high-voltage overload. Accordingly, there is no damage to, or melting or burning of, small wires in the telephone circuits at points near to or remote from the balancing resistor network. A thermistor film is screen-printed directly onto the substrate at a central region where there is no resistive film.

Abstract: There is disclosed a method and system for determining the progress of a calling connection. The system measures the peak voltage of the signals on the line and derives a ratio of these peak signals to the average value of the signal. From this ratio a determination is made as to the calling condition of the line.