VoIP Voice and Fax Signal Processing

3.7 MISCELLANEOUS NARROW AND WIDEBAND Codecs

In the previous sections, codecs of G.711, G.726, and G.729AB are considered for narrowband voice, and G.722 is considered for wideband voice. Several other codecs are presented in [Kondoz (1999), Goldberg et al. (2000), Alexander (2006), Hersent et al. (2005)], but each regional VoIP deployment may confine to a finite set of codecs. Some retail market products incorporate more types of codecs to cater to deployments in more regions and to cater to retail market options. An overview on some popular narrowbond and wideband codecs considered for VoIP applications are given in this section.

3.7.1 Narrowband Codecs

G.723.1. It is a 8-kHz sampling ITU-T Codec. G.723.1 [ITU-T-G.723.1 (2006)] is one of the popular codecs supported in many VoIP retail market products. G.723.1A is having built-in VAD/CNG functions. G.723.1 compression rates are 5.3 and 6.3 kbps. The compression at 5.3 kbps makes use of ACELP and 6.3-kbps multipulse maximum likelihood quantization (MP-MLQ). The frames are of 30 ms giving 20 or 24 bytes in 30 ms, and total algorithmic delay is 37.5 ms, including the look-ahead delay of 7.5 ms. With G.723.1, end-to-end delays also increase that result in more degradation of voice quality. Note that G.723 is an ADPCM codec for 24 and 40 kbps and is not part of G.723.1 or G.723.1A. With the incorporation of G.726 with 4-rates, G.723 became part of G.726.

G.723.1 is more attractive from a compression point of view, but G.723.1 has ...