| A file with .AMR extension is a data format originally | | | | channel is noisy, thus presenting a significant |
| developed by Ericsson. It is used by many 3G cell | | | | percentage of loss of data and resulting in cut-off |
| phones for voice recordings such as MMS messages | | | | voices and hiccups during conversation, thus when the |
| and also live voice telephony compression. It | | | | algorithm detects that the channel cannot support a |
| incorporates the Algebraic Code Excited Linear | | | | certain amount of audio quality, it will automatically |
| Prediction (ACELP) algorithm, which is designed to | | | | reduce the quality of the voice encoding. To the |
| efficiently compress human speech audio. This speech | | | | human ear the difference in quality is negligible, but this |
| encoding format algorithm is mostly used during live | | | | enables a person to talk smoothly over a period of |
| GSM telephony to adapt to the channel bandwidth and | | | | time without hiccups in transmission. The ACELP |
| noise. The AMR ACELP coder will lower the | | | | algorithm is also used to harmonize the codec |
| compression rate as cellular interference increases, | | | | standards amongst different types of cellular systems. |
| thus enabling more error correction to be applied. AMR | | | | Many modern mobile telephone handsets will allow you |
| was adopted as the standard speech codec by | | | | to store short recordings in the AMR file extension. |
| 3GPP in October 1998. | | | | There exist both Open Source and commercial |
| The ACELP algorithm uses link adaptation to select | | | | programs to convert between AMR and other |
| from one of eight different bit rates based on link | | | | formats such as MP3, although it should be noted that |
| conditions (interference and channel noise). That is why | | | | AMR encoding is a speech format and is unlikely to |
| it is called multi-rate. It is adaptive because if the | | | | give ideal results for other types of audio. |