A Digital Conference Circuit for an Instant Speaker Algorithm

When speech is transmitted over a conventional pulsecode modulation carrier the connection between two subscribers on a digital basis is straightforward. However, techniques for digital conference arrangements are not well known. Implementation of a conference arrangement using traditional analog techniques requires elaborate hardware and use of analog-to-digital converters. This paper, after a brief discussion of existing conference arrangements, describes an instant speaker algorithm and the digital circuitry employed to implement this algorithm. During every time frame an "active speaker" sample is sought. The active speaker is identified by comparing each participant's digital sample during the following time frame. The active speaker sample is transmitted to all participants in the conferencing arrangement. A "last speaker" sample is transmitted to the active speaker. The conference circuit consists of 3 modules: comparison and gating module, active speaker memory module, and last speaker memory module. The implementation of these modules with conventional transistor-transistor logic digital circuits is discussed. Overall arrangement of this conference circuit in a local digital exchange is also explored. Some comments are made concerning "on-off" patterns found in normal conversation and their relationship to the instant speaker algorithm.