HD-AAC: A HiRez lossless audio codec from the MP3 people

Fraunhofer IIS, the people who brought us MPEG-1 Layer 3, that is, the MP3, have a new codec out called HD-AAC that is part of MPEG-4. This new HD-AAC has at it’s base the AAC codec from MPEG-4 that is widely used by Apple in iTunes and on the iPod. HD-AAC adds the additional capabilities of being lossless and able to encode high resolution content, up to 192 kHz. This codec has the capability to do for HiRez content what MP3 did for standard CD music. The technology behind it is called SLS or Scalable Lossless Coding that allows you to easily adjust the bitrates without having to reencode the audio.

Most recordings these days use a higher resolution recording which is then downsampled for release. This would enable publishers to release higher resolution versions of music in a lossless format with the 50% approximate compression ratio of other lossless codecs.

The press release for the HD-AAC codec details some of the capabilities of the codec. The HD-AAC homepage on Fraunhofer’s site also contains information. Also, the MPEG working group site has some technical details.