AMR-WB
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| Adaptive Multi-Rate Wide Band (AMR-WB) | |
|---|---|
| File name extension | .awb |
| Internet media type | audio/amr-wb |
| Type of format | Audio |
Adaptive Multi Rate – WideBand (AMR-WB) is a speech coding standard developed after the AMR using same technology like ACELP. The codec provides excellent speech quality due to wider speech bandwidth of 50–7000 Hz compared to narrowband speech codecs which in general are optimized for POTS wireline quality of 300–3400 Hz. AMR-WB is codified as G.722.2, an ITU-T standard speech codec. A common file extension for AMR-WB is .awb.
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[edit] AMR modes
AMR-WB operates like AMR with 9 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 in the case of music. Also lower bit rates of 6.60 and 8.85 provide reasonable quality especially if compared to narrow band codecs.
All modes are sampled at 16 kHz 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 G722 at 64 kbit/s for clean speech; not targeted for full-rate GSM channels)
[edit] Configurations for 3GPP
When used in mobile phone networks, there are three different configurations (combinations of bitrates) that may be used for voice channels:
- Configuration A: 6.6, 8.85, and 12.65 kbit/s (Mandatory multi-rate configuration)
- Configuration B: 6.6, 8.85, 12.65, and 15.85 kbit/s
- Configuration C: 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.
[edit] Deployment
AMR-WB is already standardized for future usage in networks such as UMTS. There it provides so much higher speech quality that it seems probable that also older networks will have to gradually be transformed to support wide band.
In October 2006, first AMR-WB tests have taken place in a deployed network by T-Mobile in Germany together with Ericsson. For further details, see this link or the original T-Mobile press release (in German).
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.
[edit] See also
[edit] References
- Deep Inside the Network, Episode 2: AMR-WB - Skype-like Audio Quality for Mobile Networks
- Wideband Speech Coding Standards and Applications
- Technical Specification Group Services and System Aspects
- ITU-T Implementors' Guide for G.722.2
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