This Recommendation contains the description of an algorithm for the coding of speech signals using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP).

In its basic mode, the G.729 coder consists of a mono-rate speech coder at 8 kbits/s using fixed-point arithmetic operations. Annexes A, B and D to J extend its functionalities. Annex A provides a reduced-complexity version at the basic coding rate of 8 kbit/s. Annex B defines source-controlled rate operation for use with G.729 or Annex A. Annexes D, E and H provide multi-rate operation and specify rate-switching mechanisms: Annex D provides lower bit-rate extension at 6.4 kbit/s and Annex E provides higher bit-rate extension at 11.8 kbit/s, whereas Annex H provides bit-rate extensions at both 6.4 kbit/s and 11.8 kbit/s. Therefore, Annexes D, E and H do not implement the discontinuous transmission mode of Annex B. For this functionality, further annexes were developed. Annexes F and G use the basic algorithms in Annex B to provide discontinuous transmission (DTX) functionality for, respectively, Annexes D and E. Annex I provides DTX functionality for Annex H and describes the integration of G.729 main body with Annexes B, D and E. Annex J makes reference to the G.729 extension for the 8-32 kbit/s scalable wideband speech and audio coding algorithm in ITU-T Recommendation G.729.1, which is interoperable with G.729 and its Annexes A and B. As G.729 main body, its Annexes A, B and D to J use fixed-point arithmetic. Alternative implementations based on floating‑point arithmetic operations are provided in Annex C for G.729 and Annex A, and in Annex C+ for Annex I.

This information is summarized in the Table below.