Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1992-11-12
1995-04-25
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
379411, 379406, 379202, H04M 908
Patent
active
054105951
ABSTRACT:
The characteristics of a room in which a speakerphone (20) is located are measured by determining a time between a test signal and its first attack, and a number of sample periods between the first attack and a time when the average power in the echo falls below a threshold. The first-attack time determines a pre-filter delay and the number of sample periods determines a tap length for an adaptive echo-canceling filter (62). In a teleconferencing environment, an annoying initialization sequence is avoided by initializing filter coefficients for each microphone (140), and saving the initial filter coefficients generated thereby in a corresponding nonvolatile memory (104). In response to an off-hook signal, the coefficients are retrieved from the nonvolatile memory (104). During operation, the coefficients are constantly updated. If another microphone (141) is enabled, the stored coefficients corresponding to that microphone (141) are dynamically substituted for the present coefficients.
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"Full-Duplex Speakerphone With Acoustic and Electric Echo-Canceller Utilizing the DSP56200 Cascadable Adaptive FIR Filter Chip," Sangil Park, Proc. of Midcon/90 Tech. Conf. on Electronic & Electrial Tech., Dallas, Tex., Sep. 11-13, 1990.
Funderburk Dion M.
Park Sang-il
Dwyer James L.
Motorola Inc.
Polansky Paul J.
Weaver Scott L.
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