Tools for Signal Compression: Applications to Speech and Audio Coding

Chapter 8

Audio Coding: Additional Information

The development of high-quality, reduced bit rate perceptual coders has been the subject of strenuous research efforts for the past 20 years. At the time of writing, the most successful coder is the Audio Advanced Coder (AAC) in MPEG-2 and MPEG-4. Improvements, primarily through the introduction of new tools, are still being made. In this chapter, two recent and characteristic developments are presented: research into good-quality, low bit rate coders and very good quality or even lossless coders. Throughout, we note that these developments do not at all deliver the same compression rates and are consequently not of the same level of interest. Making available a low bit rate coder while maintaining an acceptable quality is of considerably greater interest to operators than making available of lossless coder that has a low compression rate. That being said, the lossless coder is presented in this book because it has an interesting property from an educational perspective: the algorithms used in this particular coder are directly adapted from algorithms developed in image coding. This convergence of audio coding and image coding is sufficiently rare to be worth noting.

In this chapter, these recent developments of the AAC are presented relatively briefly. In the following chapter, a more extensive study of the dedicated stereo coding tool is presented.

8.1. Low bit rate/acceptable quality coders

The audio coder HE-AACv2 developed in ...