An ITU standard CS-ACELP codec that converts analog speech to or from a stream of digital data. G.729 employs data compression techniques so that a voice conversation that would normally take 64Kbps of bandwidth (using G.711) can be transmitted using only 8Kbps.

Requiring a lower data-rate allows G.729 to utilize available bandwidth more efficiently but also makes the call much more fragile in the face of network transmission impairments such as packet loss. It also reduces the legibility, especially in situations where the signal is re-digitized multiple times (such as when a digital cordless phone is used).

G.729 uses CS-ACELP compression algorithm, which boasts low latency times of 15ms.