Sgs-Thomson Microelectronics S.r.l.

Francesco Natali

Angelo Pariani

A method of attenuating the echo signal in so-called telephone fork converting circuits, adapted for telephone conferences with a plurality of participants, consists of switching and arranging sequentially on a serial line messages from each participant as coded in the PCM code, by means of a digital switching array, and of performing a sign reversal on the PCM codings of a number of messages equal to the approximation to the nearest number below the number of participants in the conference divided by two. In the instance of an odd number of participants, first and second conferences are set up by means of a conference actuator, each conference comprising a different combination of inverted-sign coded messages and remaining coded messages from the participants, with consequent cancellation of the echo components having opposite sign; subsequently, on the double-wire receiving line associated with the telephone fork of each participant, one of said conferences is transmitted as deprived of the message related to that participant including a number of inverted-sign messages equal to that of the remaining original messages.

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Bartolomeo, Italy

Francesco Natali