Mobile phone codecs adapt their bit rate across eight levels to optimize call quality

Evidence

In CELP, the residual signal is not sent as a signal, only a few parameters describing the residual are transmitted, which gives a significantly better speech quality at low bit rates. In VoIP applications, the codec commonly used is the conjugate-structure algebraic code-excited linear prediction (CS-ACELP) codec specified in standard G. (Salami et al., 1998). The adaptive multi-rate (AMR) codec is commonly used in mobile phones (ETSI, 2011). It was standardized by the European Telecommunications Standards Institute (ETSI) in 1999. It is based on the ACELP technique, and is also able to use in transmission eight different bit rates ranging from 4.75 kbps up to 12.2 kbps. This enables adaptive allocation of bit stream resources to maximize the quality of experience. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2221

Categorization

• XREF: Connects to the reader’s acoustic engineering background on codec standards (G.729 CS-ACELP, AMR-NB).