Vector quantization of scale factors in advanced audio coder (AAC)

This paper describes some experiments to reduce the load of the side information in the MPEG advanced audio coder (AAC) scheme using vector quantization (VQ) methods. The VQ replaces the existing differential and entropy coding of the scale factors. Various types of VQ are considered, such as sub-vector VQ, multi-stage VQ and tree-structured VQ which provide some advantages in the context of MPEG-4 AAC characteristics such as scaleability etc. However, the VQ being a lossy compression scheme, psycho-acoustic sensitivity of the losses is very important. These are studied using objective measures such as NMR and listening tests to make proper choices for the VQ design