Abstract: A method and circuit for nulling each talker's speech in a conference call having a plurality of parties who are selectively talkers and listeners. The parties are interconnected on PCM telephone carrier lines (T1 or CEPT) which are connected to a digitized conference bridge. The circuit of the present invention has a summation circuit for adding together all of the speech data on the carrier lines occurring in the conference call during a particular time slot. A circuit is used for delaying the speech of each individual talker. Finally, the circuit of the present invention utilizes a subtraction circuit for subtracting the delayed speech of each individual talker from the summation of all speech for delivery back to the ears of the individual talker. The delaying circuit precisely delays the speech of each individual talker so as to corespond in timing with the output of the summation circuit.

Abstract: A digital teleconferencing control device, system and method are disclosed for use in telecommunications. A digital conference control circuit having pulse code modulation and time division multiplexing is used in connecting a plurality of telephone subscribers together for conference purposes. When so connected, a plurality of then selected speakers can be heard by all other subscribers connected into the conference with the number of subscribers connectable into the conference being unlimited. Logic gates at the digital level in the control circuitry prevents return of signals generated by a speaking subscriber back to that subscriber.