49 - Sound Distribution including Digital Sound-in-sync

Abstract

This chapter discusses sound distribution. The networks that are used for program production and to feed the transmitters must also be upgraded to carry two or even three audio channels. Where the digital system is used for broadcasting, it is highly desirable to use digital systems for networking to ensure that the broadcast sound quality is not limited by analoe distribution networks. To reduce the cost of television signal distribution by eliminating the need for separate sound circuits, the BBC, in the 1960s, proposed a novel way of carrying the sound signal as part of the video waveform. They developed the first sound-in-sync equipment, the design of which was later licensed for manufacture by Pye TVT Ltd of Cambridge, England. As the name implies, the principle is to make use of the time available during the sync pulse periods of the television waveform to carry sound signals. While the terms stereo and dual channel are often used interchangeably, there are small differences in the technical requirements of systems to carry stereo and dual language services. The NICAM 728 system is the basis of the EBU recommended system for the transmission of two- channel digital sound channels with terrestrial television systems B, G and I. The system is based on the addition of a new carrier, which is digitally modulated with a continuous 728 kbit/s signal, to the existing television transmission.