Sound Carriers in the Form of Magnetic Tape, Sound Carriers in the Form of Optical Tape Either of the Variable Density or the Variable Amplitude Type, Sound Carriers in the Form of Grooved Record Discs, Automatic Play Back Machines, Including Master Units and Slave Units, Relay Network Systems for Transmitting Sound Representing Signals from a Central Transmitting Station to One or Several Remote Sound Reproducing Stations, Including Loud Speaker Equipment, Tape Duplicators and Cassettes for ...