Transmission systems for audio and/or video and related signals using infra-red radiation. Digital audio signals for conference and similar applications|Bandwidths, Control signals, Digital signals, Audio systems, Control systems, Telecommunication systems, Telecommunication transmission methods, Analogue signals, Receivers, Frequency modulation, Modulation, Marking, Remote control systems, Optical communication systems, Video signals, Noise (spurious signals), Signals, Transmitters, Television equipment, Data transmission, Pulse modulation, Public-address systems, Infrared radiation, Communication equipment, Position, Video tape recorders, Audio equipment, Compatibility, Acoustic signals