Adaptive Multi-Rate Wideband (AMR-WB) is a patented speech coding standard developed based on Adaptive Multi-Rate encoding, using similar methodology as Algebraic Code Excited Linear Prediction (ACELP). AMR-WB provides improved speech quality due to a wider speech bandwidth of 50–7000 Hz compared to narrowband speech coders which in general are optimized for POTS wireline quality of 300–3400 Hz. AMR-WB was developed by Nokia and VoiceAge and it was first specified by 3GPP.
AMR-WB is codified as G.722.2, an ITU-T standard speech codec, formally known as Wideband coding of speech at around 16 kbit/s using Adaptive Multi-Rate Wideband (AMR-WB). G.722.2 AMR-WB is the same codec as the 3GPP AMR-WB. The corresponding 3GPP specifications are TS 26.190 for the speech codec and TS 26.194 for the Voice Activity Detector.[1][2][3]
AMR-WB codec has the following parameter:[4]
A common file extension for AMR-WB file format is .awb. There also exists another storage format for AMR-WB that is suitable for applications with more advanced demands on the storage format, like random access or synchronization with video. This format is the 3GPP-specified 3GP container format based on ISO base media file format.[5] 3GP also allows use of AMR-WB bit streams for stereo sound.
AMR-WB operates, like AMR, with nine different bit rates. The lowest bit rate providing excellent speech quality in a clean environment is 12.65 kbit/s. Higher bit rates are useful in background noise conditions and for music. Also lower bit rates of 6.60 and 8.85 kbit/s provide reasonable quality especially if compared to narrow band codecs.
All modes are sampled at 16 kHz (using 14-bit resolution) and processed at 12.8 kHz.
The bit rates are the following:
- Mandatory multi-rate configuration
- 6.60 kbit/s (used for circuit switched GSM and UMTS connections; should only be used temporarily during bad radio connections and is not considered wideband speech)
- 8.85 kbit/s (used for circuit switched GSM and UMTS connections; should only be used temporarily during bad radio connections and is not considered wideband speech; provides quality equal to G.722 at 48 kbit/s for clean speech)
- 12.65 kbit/s (main anchor bitrate; used for circuit switched GSM and UMTS connections; offers superior audio quality to AMR at and above this bit rate; provides quality equal to or better than G722 at 56 kbit/s for clean speech)
- Higher bitrates for speech in adverse background noise environments, combined speech and music, and multi-party conferencing.
- 14.25 kbit/s
- 15.85 kbit/s
- 18.25 kbit/s
- 19.85 kbit/s
- 23.05 kbit/s (not targeted for full-rate GSM channels)
- 23.85 kbit/s (provides quality equal to G.722 at 64 kbit/s for clean speech; not targeted for full-rate GSM channels)
When used in mobile phone networks, there are three different configurations (combinations of bitrates) that may be used for voice channels:
- Configuration A (Config-WB-Code 0): 6.6, 8.85, and 12.65 kbit/s (Mandatory multi-rate configuration)
- Configuration B (Config-WB-Code 2): 6.6, 8.85, 12.65, and 15.85 kbit/s
- Configuration C (Config-WB-Code 4): 6.6, 8.85, 12.65, and 23.85 kbit/s
This limitation was designed to simplify the negotiation of bitrate between the handset and the base station, thus vastly simplifying the implementation and testing. All other bitrates can still be used for other purposes in mobile phone networks, including multimedia messaging, streaming audio, etc.
AMR-WB has been standardized by a mobile phone manufacturer consortium for future usage in networks such as UMTS. Its speech quality is high, but older networks will have to be upgraded to support a wide band codec.[citation needed]
In October 2006, first AMR-WB tests were conducted in a deployed network by T-Mobile in Germany, in cooperation with Ericsson.[6][7]
In 2007 end-to-end AMR-WB TrFO capable 3G & VoIP product line was commercially released by NSN (M13.6 MSS, U3C MGW). AMR-WB TFO support commercially released in 2008 (M14.2, U4.0). End-to-end TFO/TrFO negotiation and mid-call optimization (e.g. on handover, CF or CT events) released in 2009 (M14.3, U4.1).
In late 2009, Orange (UK) announced that it would be introducing AMR-WB on its network in 2010.[8][9] In France Orange and SFR are using this codec on their 3G+ networks since the end of 2010 summer.
WIND Mobile in Canada launched HD Voice (AMR-WB) on its 3G+ network in February, 2011. WIND Mobile also announced that several handsets will support HD Voice (AMR-WB) in first half of 2011. WIND Mobile press release on HD voice First one being Alcatel Tribe.[10]
Nokia developed VMR-WB codec for CDMA2000 networks, which is fully interoperable with 3GPP AMR-WB.
AMR-WB is also widely adapted format in mobile handsets for tones.
The AMR wideband speech codec shall be supported in 3G multimedia services when wideband speech working at 16 kHz sampling frequency is supported. This requirement is defined in 3GPP technical specifications for IP Multimedia Subsystem (IMS), Multimedia Messaging Service (MMS) and Transparent end-to-end Packet-switched Streaming Service (PSS).[11][12][13] In 3GPP specifications is AMR-WB format also used in 3GP container format.
G.722.2 is licensed by VoiceAge Corporation.[14][15][16][17]
In order to create samples, one can use Nokia's conversion tool to create both .amr and .awb files. Nokia Multimedia Converter 2.0 can be donwloaded from here: http://www.developer.nokia.com/info/sw.nokia.com/id/d1c17a7f-1231-4385-8c17-04f28f4f2d8e/Nokia_Multimedia_Converter_2.0.html It works in Windows 7 as well if the setup is run in XP compatibility mode.
For decoding, an open source library exists: OpenCORE.
For encoding, an open source library exists as well: Android VisualOn.
Both can be incorporated in ffmpeg (meaning ffmpeg can be compiled with --enable-libopencore-amrwb --enable-libvo-amrwbenc ).
