MULTIMEDIA CODING TECHNOLOGY

Every medium, such as speech, sound, and pictures, can be processed in the same manner by expressing the information in discrete digits usin g bit-reduced coding. Therefore, coding is a key technology for multim edia services. In particular low bit-rate coding is required for perso nal communications because of the limited available radio frequency ba ndwidth. This paper describes PSI-CELP, CS-CELP, and Twin VQ proposed by NTT for speech and sound coding at bit-rates of less than 64 kbit/s , the key range for personal communications. PSI-CELP has been adopted as the personal digital cellular standard in Japan for a half bit-rat e (5.6 kbit/s) digital cellular mobile radio system. CS-CELP, at 8 kbi t/s, has coded speech quality equivalent to 32 kbit/s ADPCM, which has been used in NTT's personal handy phone system (PHS). NTT proposed it as a candidate for 8-kbit/s speech coding standardization in the ITU. Finally, Twin VQ at 64-16 kbit/s has coded music quality equivalent t o a compact disc. In the future, bit-rate reduction without degradatio n of speech/sound/picture quality or processing delay will be studied for multimedia services in personal communications.