A time shared multiport conference arrangement includes an additive PCM speaker circuit. The additive PCM speaker circuit eliminates the need for loudest speaker detection and the last speaker memory of conventional conferencing arrangements. The additive PCM speaker circuitry operates in an on-line,...http://www.google.de/patents/US4831618?utm_source=gb-gplus-sharePatent US4831618 - Additive PCM speaker circuit for a time shared ISDN conference arrangement
