CCITT Standardizing activities on speech coding

CCITT (International Telegraph and Telephone Consultative Committee) Study Group XVIII is in charge of studies on speech processing, such as speech coding techniques. During its last study period (1981-84), a recommendation for 32 kbit/s speech coding was made. Afterwards, Study Group XVIII began standardization studies on wideband speech coding (i.e., 7 kHz audio coding) at 64 kbit/s or less. This paper reports on the progress of these standardization studies. The 32 kbit/s Adaptive Differential PCM (ADPCM) standard is briefly reviewed. Also, the 7 kHz audio coding at 64 kbit/s or less is mainly discussed focussing on its applications, design requirements and coding algorithm.