The application of digital methods to the internal distribution of high-quality sound signals in a broadcasting system allows a high and predictable standard of technical quality to be maintained with the minimum of attention by operating staff. Pulse-code-modulation systems for the incorporation of a sound signal into a video waveform and for the multiplex distribution of programmes for the radio service will soon be in operation within the BBC, and the eventual use of national and international digital links for this purpose is envisaged. The feasibility of digital recording has also been demonstrated. This paper is mainly concerned with the special requirements to be met in the digital coding and decoding of broadcast-quality sound signals. Considerations of quantising noise, distortion and digit-error detection lead to a bit rate approaching half a megabit per second per channel, though this rate may be somewhat reduced as a result of current developments in digital companding. No attempt is made to deal with aspects of point-to-point transmission which are common to other digital systems, but the effects of digit-error rate and of timing jitter are considered, and tolerances are suggested.