Adaptive Multi-Rate (AMR)

What is Adaptive Multi-Rate (AMR)?
Adaptive Multi-Rate is a codec based on an audio compression format used for speech coding. It is considered a hybrid of speech codes and can transmit both waveform signals and speech parameters. It is a mandatory voice codec for most third generation (3G) cellular systems and is a preferred codec for the Global System for Mobile Communications (GSM) standard. Adaptive Multi-Rate offers superior audio performance, better coverage and quality, and is easier to implement than previous formats.

The Adaptive Multi-Rate Codec offers speech rates from 4.75 to 12.2 kbit / s.The associated sampling frequency is 8 kHz with speech coding occurring at 20 ms frames. It also uses technologies such as comfort noise generation, discontinuous transmission, and voice activity detection to reduce bandwidth usage during quiet times. One of the special features of Adaptive Multi-Rate is its adaptability to radio channel environments and the selection of optimal speech in contrast to other speech codecs which operate with a fixed degree of error protection and at a fixed rate. In poor radio conditions, the channel coding is increased and the source coding is decreased in the case of the adaptive multi-rate. Adaptive Multi-Rate uses the link adaptation to select one of the eight possible bit rates.

Adaptive Multi-Rate offers many advantages over other codecs. It can be tailored to the different needs of the operator. It can also bring improved voice quality with the help of the codec mode adjustment even in half-rate mode. It has better performance control and handover compared to other codecs. It also has increased resistance to glitches and errors.