Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1993-05-14
1994-10-04
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379411, 379388, 379389, 379390, 370 321, H04M 908
Patent
active
053533488
ABSTRACT:
A double echo cancelling system includes comparators which monitor, respectively, "unmodified" signals from the near end or far end and "modified" signals from the other end. The unmodified signals are the signals received by the system and the modified signals are those signals which have been subjected to echo cancellation and attenuation. A comparator determines that a caller at one end is speaking if the associated unmodified signals exceed by more than a predetermined value the modified signals associated with the other end. The comparator which detects near end speech controls the adaptation of an associated adaptive filter and the operation of a cancellation monitor, which, in turn, controls the adaptation of the adaptive filter associated with the far end. When this comparator detects near end speech, it enables the cancellation monitor. The monitor compares the power of the unmodified far end signals with the power of the residue signals produced by an associated subtraction circuit, and enables adaptation of the associated adaptive filter if the residue signals exceed the unmodified signals by more than a predetermined amount. Otherwise, the monitor inhibits adaptation. Attenuation control circuitry uses the speech detection signals from both of the comparators to control the gain of near end and far end signal attenuators. If only one end is active, the controller increases the gain of the appropriate attenuator; if both ends are active simultaneously, it leaves the attenuators in their current states; and if neither end is active it decreases the gain of both attenuators.
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Austin Jahangir E.
Sendyk Andrzej
Dwyer James L.
Fournier Paul A.
JRC International, Inc.
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