G.729 is an ITU-T audio data compression standard that operates at 8 kbit/s using a conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP). This algorithm for voice compresses voice audio in 10 millisecond frames. G.729 is commonly used in in Voice over IP (VoIP) applications because of its inherently low bandwidth requirement. Extensions to the G.729 standard include the following;
- G.729a (G.729 Annex A) – Compatible with G.729 Annex A specifies a coder with several simplifications, including code book search routines. These modifications are known to often result in a slightly lower voice quality.
- G.729b (G.729 Annex B) – Compatible with G.729, Annex B specifies a coder that uses Discontinuous Transmission (DTX), Voice Activity Detection (VAD), and Comfort Noise Generation (CNG) to reduce bandwidth usage. Bandwidth is reduced by preventing the transmission of non-voice during periods of silence.
See G.7xx for more information on how these standards are used in telephony networks.