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Abstract

A three-party conference circuit provides for three-party conference calls in time-division-multiplex communication systems utilizing pulse-code modulation. The digitized speech signals from a selected group of channels are received from an incoming PCM highway, expanded from PCM coding to linear coding and consecutively stored in groups of three in three registers. Different pairs of the registers are selected by a multiplexer, after which the speech signals from the selected pairs of registers are added to provide a combined speech signal. The combined speech signals are compressed from linear coding to PCM coding and applied to an outgoing PCM highway for transmission to the respective parties. Since the speech signals are combined and retransmitted essentially within the same frame, time delay distortion of the audio signals is minimized. In addition, the three-party conference circuit provides for a diagnostic mode of operation where incoming speech signals are retransmitted and a broadcast mode of operation where the speech signals from one channel are combined with each of the other channels of the selected group of channels to be transmitted.

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First Claim