Adaptive Multi-Rate audio codec: Difference between revisions

Revision as of 12:27, 30 October 2017

Revision as of 11:18, 23 January 2018

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== Usage ==

The frames contain 160 samples and are 20 milliseconds long.<ref name="3gpp-26090" /> AMR uses various techniques,

The frames contain 160 samples and are 20 milliseconds long.<ref name="3gpp-26090" /> AMR uses various techniques, such as [[algebraic code excited linear prediction|ACELP]], [[discontinuous transmission|DTX]], [[voice activity detection|VAD]] and [[comfort noise|CNG]]. The usage of AMR requires optimized link adaptation that selects the best codec mode to meet the local radio channel and capacity requirements. If the radio conditions are bad, [[source coding]] is reduced and [[channel coding]] is increased. This improves the quality and robustness of the network connection while sacrificing some voice clarity. In the particular case of AMR this improvement is somewhere around S/N = 4–6&nbsp;dB for usable communication. The new intelligent system allows the network operator to prioritize capacity or quality per base station.

There are a total of 14 modes of the AMR codec, eight are available in a full rate channel (FR) and six on a half rate channel (HR).

{| class="wikitable"

! Mode !! Bitrate (kbit/s) !! Channel !! Compatible with

|-

| AMR_12.20 || 12.20 || FR || [[Enhanced full rate|ETSI GSM enhanced full rate]]

|-

| AMR_10.20 || 10.20 || FR ||

|-

| AMR_7.95 || 7.95 || FR/HR ||

|-

| AMR_7.40 || 7.40 || FR/HR || [[IS-641|TIA/EIA IS-641 TDMA enhanced full rate]]

|-

| AMR_6.70 || 6.70 || FR/HR || [[PDC-EFR|ARIB 6.7 kbit/s enhanced full rate]]

|-

| AMR_5.90 || 5.90 || FR/HR ||

|-

| AMR_5.15 || 5.15 || FR/HR ||

|-

| AMR_4.75 || 4.75 || FR/HR ||

|-

| || || ||

|-

| AMR_SID || 1.80 || FR/HR ||

|-

|}

== Features ==