Abstract: A system for control of speech direction in duplex telephone circuits (e.g. hands-free telephones), derives a switching control signal proportional to both the immediate transmit-channel signal value, and a Regulating Value which is the ratio of the Receive-Channel Signal to the Transmit-Channel Signal under no-local-sound-source condition. Thus the Regulating Value is proportional to the local acoustic feedaround (Overhearing) signal between local loudspeaker to microphone. The Regulating Value responds to faster variations (caused by speech) to cause direction-switching, but merely compensates for slower variations (caused by movement of people or microphone in the local room). Switching (Breakthrough) of the microphone to On and the loudspeaker to Off also depends on the magnitude of the closed-channel (non-connected) microphone signal exceeding that of the open channel.

Abstract: A system for addressed time multiplexed telecommunication comprising subscribers apparatus whose address selector supplies voltage levels which in a central exchange are converted to binary form and stored in address shift registers. Taken out of the registers the addresser's and addressee's addresses are converted to analogue form and compared with a step voltage from a step voltage generator, and the result of the comparison controls analogue switches which make the connection between the addresser and the addressee and break the connection when addresser or addressee presses an off-button.