Introduction Technological developments presently allow the emission of digitally encoded audio signals to the public to be envisaged. It would be possible in particular to introduce this technique in the broadcasting-satellite service. This will require the prior definition of characteristics concerning coding@ multiplexing and modulation of audio signals. This Report is concerned only with digital sound coding. Multiplexing@ bit-error protection strategy and modulation aspects are discussed in Reports 954 and 632 respectively. Information dealing with methods of error correction or concealment can be found in Report 1073. Study Programme 51 C/ 1 0 considers that the introduction of digital techniques for emission should allow an improvement in the quality of the signals transmitted. Recommendation 651 deals with digital PCM coding. Results of objective and subjective tests are given in Annex II of the present Report. Other coding methods leading to a substantial bit rate reduction and at the same time maintaining very high quality are described in Report 1199. In addition to the improvement pf quality@ the following should be considered: ?? the compromises between quality objectives and bit rate may be different for sound services which may have various quality requirements and planning constraints; ?? they may also vary according to the requirements of individual countries; there are clear advantages for broadcasters@ receiver manufacturers and the public in using a single standard for each application.