Bitrate and Tandem Detection for the AMR-WB Codec with Application to Network Testing

In network testing, identifying the cause for an observed speech quality degradation is of special interest. Common speech codec related causes to be identified are the application of a low bitrate or the occurrence of transcoding or self-tandem. This paper presents two comprehensible types of signal features which enable a speech-quality-motivated bitrate detection for the AMR-WB codec. The first type of feature is based on codec linearity, while the second type exploits the different structure of the fixed codebook at each bitrate. With these underlying features, the bitrate detection is performed with high accuracy. Since the one feature gathers information on the last applied bitrate and the other on coding effects accumulated during the entire transmission, this paper, additionally, provides a method to extract information on the occurrence of self-tandem in the network-under-test.