Abstract :
Broadcasting, as a medium for the dissemination of stereophonic programmes, presents a number of technical and economic problems over and above those encountered in the production of commercial recordings. Although much of the programme material at present broadcast could, as far as technical quality is concerned, be equally well, or in some cases better, produced by prerecording, certain types of item still require to be transmitted ?live?. In stereophonic transmissions, various problems associated with the disposition and movement of artists in the studio are then aggravated, while difficulties are encountered in the distribution of the programme over long trunk routes because of fortuitous differences in time delay between the left- and right-hand channels. Various methods have been proposed for broadcasting simultaneous monophonic and stereophonic versions of the same programme without an increase in the number of transmitters. To this end, the monophonic and stereophonic signals are derived from the same set of microphones, a compromise which in some cases makes it difficult to achieve complete compatibility, i.e. optimum performance in both systems simultaneously. Possible methods for achieving compatible monophonic and stereophonic transmissions on a single channel include frequency- or time-division multiplex, involving in some cases a combination of phase- and amplitude-modulation. Most of these systems require some increase in radiated power for a given service area, but others, still under development, aim at overcoming this difficulty by confining the directional information transmitted to one or more narrow-band ?steering? signals. In television transmission the judicious use of stereophony could enhance the realism of the picture, but in all but the simplest cases, the microphone technique necessary to avoid incongruity between vision and sound would probably make the latter unsuitable for monophonic reception in the sound service. The engineering effo- - rt required to provide nation-wide stereophonic broadcasting without detriment to existing services could be justified only by a sufficient public demand; this last factor depends in turn on the potentialities of stereophony when applied to a wide variety of programmes, a subject which has yet to be fully explored.
