VoIP Voice and Fax Signal Processing

3.6 G.729 FAMILY OF LOW-BIT-RATE Codecs

The G.729 family of codecs are popularly used in most VoIP deployments. G.729 [ITU-T-G.729 (1996)] is an ITU-T G.729 recommendation for a conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP) speech compression algorithm. G.729 makes use of human vocal tract models suitable for voice signals unlike the G.711 and G.726 codecs, which use waveform-based compression. Basic G.729 compresses voice to 8 kbps, which provides eight times more compression than G.711 and provides good voice quality.

G.729 Annex A (G.729A) is the reduced complexity version of the G.729 recommendation, and it compresses voice to the same 8 kbps [ITU-T-G.729A (1996)] with the tradeoff of a slight loss of quality in comparison with G.729. This version is developed mainly for multimedia simultaneous voice and data applications, although the use of the codec is not limited to these applications. G.729A is bit stream interoperable with the full version of G.729. This codec has built-in packet loss concealment. The codec with suffix B denoted as G.729B or G.729AB supports VAD in the encoder and CNG in the decoder [ITU-T-G.729B (1996)]. G.729 has a wide family of codecs, and some of the popular codecs are listed in Table 3.3. In VoIP deployment, G.729AB is popularly used. In the wideband upgrade, these codecs may be replaced with G.729.1. These wideband codecs are interoperable with narrowband versions. Hence, a wideband codec alone should be sufficient for ...