AMR File

AMR stands for Adaptive Multi Rate. AMR is a common audio file format that is used for various mobile devices such as cell phones and other mobile devices for various applications that ranges from normal audio player / recorder to VoIP kind of applications. AMR files are mainly optimized for recording speech i.e. for creating voice messages and voice memo on cell phones. It was developed by Ericson and became the standard speech codec in 1998. AMR is well supported by most of modern mobile telephone handsets.

These are the compressed audio files that are extensively used by many 3G cell phones for voice recordings such as MMS messages. It incorporates the Algebraic Code Excited Linear Prediction (ACELP) algorithm that can to securely compress human speech audio. However, AMR file does not provide good audio quality for audio playback i.e. non-voice content.

AMR is the only narrowband speech codec that provides eight different bit rates, which can be adapted according to the network congestion. This enables the significant enhancement in Quality of the audio. AMR files uses link adaptation technique to select from one of eight different bit rates based on link conditions.

File Extension: .amr
Mime type: audio/amr

Types of AMR files:

Essentially there are two types of AMR file formats; AMR- Narrow Band and AMR-Broad band. Below is the brief description of the two:

AMR-NB (Narrowband): This version is commonly used in situations like basic voice recording on your MP3 player, where low bitrates are sufficient. The frequency range used for AMR-NB is 300-3400 Hz which can produce sound quality equivalent to traditional telephone. This narrowband version uses the bitrates of 04.75 kbps, 05.15 kbps, 05.90 kbps, 06.70 kbps, 07.40 kbps, 07.95 kbps, 10.20 kbps, 12.20 kbps.

AMR – WB (Wideband):  As the name suggests, this is an enhanced vocoder and uses a wider bandwidth than AMR-NB. It stores voice at a much higher quality i.e. the frequency range used in this ranges between 50 -7000 Hz. Because of its higher frequency range and superior speech quality, AMR-WB is improved for use in GSM (Global System for Mobile Communications) i.e. 2G technology and UMTS (Universal Mobile Telecommunications System) i.e. 3G technologies.

The bitrates used for AMR Wideband version includes, 06.60 kbps, 08.85 kbps, 12.65 kbps, 14.25 kbps, 15.85 kbps, 18.25 kbps, 19.85 kbps, 23.05 kbps, 23.85 kbps.

Main features of AMR:

• AMR codec uses eight basic bit rates 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbps.
• AMR utilizes Discontinuous Transmission (DTX) in combination with the Voice Activity Detection (VAD) and Comfort Noise Generation (CNG), this reduces the use of bandwidth during a quiet sound
• Coded AMR media can be encapsulated in the 3GP or MPEG-4 file formats and used along the entire delivery chain in multimedia applications.

Applications of AMR

• Multimedia services for 3G mobile communication systems
• Unified Messaging
• Content creation tools and content downloads
• Internet applications
• Streaming
• Voice over IP
• Portable audio devices
• Conferencing
• Wi-Fi telephony
• Digital radio broadcasting

These AMR files are very prone to data loss, in case your AMR file get lost or deleted and you want to perform AMR recovery, then click on the given link.