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Concept
Adaptive Multi-Rate Wideband
Summary
Adaptive Multi-Rate Wideband (AMR-WB) is a patented wideband speech audio coding standard developed based on Adaptive Multi-Rate encoding, using a similar methodology to 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.
The AMR-WB format has the following parameters:
Frequency bands processed: 50–6400 Hz (all modes) plus 6400–7000 Hz (23.85 kbit/s mode only)
Delay frame size: 20 ms
Look ahead: 5 ms
AMR-WB codec employs a bandsplitting filter; the one-way delay of this filter is 0.9375 ms
Complexity: 38 WMOPS, RAM 5.3 kilowords
Voice activity detection, discontinuous transmission, comfort noise generator
Fixed point: bit-exact C code
Floating point: under work
A common for the 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 the . 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 when compared to narrow-band codecs.
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Official source
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