A Very Low Bit Rate Protection Layer to Increase the Robustness of the AMR-WB+ Codec against Bit Errors
Philippe Gournay · Journal of the Audio Engineering Society · 2007
Audio codecs face various channel impairments when used in challenging applications such as digital radio. The standard AMR-WB+ audio codec includes a concealment procedure to handle lost frames. It is also inherently robust to bit errors, although some bits within any given AMR-WB+ frame are more sensitive than others. With this in mind, the present paper makes two contributions. First, a detailed study of the sensitivity of individual bits in AMR-WB+ frames is provided. All the bits in a frame are then divided into three sensitivity classes so that an efficient unequal error protection (UEP) scheme can be designed. Then, a very low bit rate protection layer to increase the robustness of the codec against bit errors is proposed and assessed using subjective audio quality tests. Remarkably, in contrast to the standard codec, where some errors have a very discernable effect, the protection layer ensures that the decoded audio is free of major channel artifacts even at a 0.5% bit error rate.