This paper presents a source-controlled, variable bit rate extension to the AMR-WB+ standard audio codec. AMR-WB+ allows multi-rate operation and in particular rate switching at every frame. However, the standard does not support source-controlled rate determination since it does not include a signal classifier. The proposed extension includes a signal classifier and rate mapping function for each signal class. Classification is performed at a lower frame rate compared to AMR-WB+, with typically 1 classification decision every second. Significant rate savings can be achieved by encoding speech at lower rates than other signals such as music. Applications include audio broadcasting over packet networks and storage of multimedia signals with mixed signals in the audio track.
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