Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1985-05-07
1987-07-07
Rubinson, Gene Z.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
370 321, H04B 320
Patent
active
046792309
ABSTRACT:
This arrangement is intended to control the operation of the coefficients adjusting circuit (12) of an echo canceller and of the operation of a center clipper (15) inserted in the send path (7) of a four-wire circuit at the output of the subtractor (13) of the echo canceller for suppressing there, when it is set to its active state, the signals whose amplitude is lower than or equal to a clipping threshold. The control arrangement operates on the basis of the signal in the receive path (2) of the four-wire circuit, the level N.sub.REC of this signal and the levels N.sub.AV and N.sub.AP of the signals before and after the subtractor (13). It comprises a controller (21) for comparing the level N.sub.AV to two fixed thresholds N.sub.AV0, N.sub.AV1 and for comparing the ratio N.sub.AP /N.sub.AV to a threshold a which is capable of varying as a function of N.sub.AV, the center clipper being only set to its active state when the level N.sub.AV is comprised between N.sub.AV0 and N.sub.AV1 and the ratio N.sub.AP /N.sub.AV is below a threshold a, the clipping threshold varying in accordance with an increasing function of the level N.sub.AV.
REFERENCES:
patent: 3894200 (1975-07-01), Campanella et al.
patent: 4282411 (1981-08-01), Stewart
patent: 4360712 (1982-11-01), Horna
"Echo Canceller Utilizing Pseudo-Logarithmic Coding", D. Horna, NTC '77 Conference Record, Los Angeles, Calif., Dec. 5-7, 1977, pp. 379-406.
"Report of the Working Party on Voice Processing", International Telegraph and Telephone Consultive Committee, Study Group XV-Report No. R24, pp. 16-22, Jan. 1983.
Dagorn Christian
Lassaux Jean
Barschall Anne E.
Eason Leroy
Rubinson Gene Z.
Telecommunications Radioelectriques et Telephoniques T.R.T
Vaas R.
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