The ITU-T Recommendation for adaptive differential pulse code modulation (ADPCM) voice encoding at 40, 32, 24, and 16 kbps. See also ADPCM, G series, and ITU-T.
An ITU standard for speech codecs that uses the ADPCM method to compress 64 Kbps PCM into 40, 32, 24 or 16 Kbps depending on available channel bandwidth. G.726 generally replaces G.721 and G.723. See G. standards, G.727 and ADPCM.