People under the stairs just released a new album called Highlighting using a new codec called HD-AAC (also known as MPEG-4 SLS) that was created by Fraunhofer.

Basically it's a file that contains both a lossy AAC version and a lossless "HD-AAC" version but in about the same file size as an all lossless ALAC file. So it can be played by any software/hardware that plays AAC, but the lossless part can only be played by an HD-AAC decoder.

According to the video from Thes One and some comments by someone that worked on the production on this page: http://pl70.net/highlighter-hd-aac the files should be playable in lossless by iTunes and newer iPods/iPhones. However, I'm 99% sure they are misunderstanding the format and only the lossy version is playing. iTunes identifies the songs as 192kbps AAC files and makes no mention of HD-AAC. Also I can't find a single spec sheet or piece of information online that says that they (or any software/hardware for that matter) actually support anything more than the AAC core.

Also, I found this video of a Fraunhofer representative that explicitly states that iPods don't support the lossless portion of the audio (skip to 3:57 in):

Can anyone point me to a piece of software that can be used to play or convert the lossless portion of HD-AAC audio?

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    – Dipan Mehta
    Commented Mar 15, 2012 at 20:02

2 Answers 2


I would go to VLC in the first instance. It's benefits include:

  • Great format support
  • Cross platform
  • Free

Here is a handy list of the formats supported; it indicates that it supports "AAC - MPEG-4 part3". This article on Wikipedia also gives a good list of alternative players that support either the encoding or decoding of MPEG-4 SLS.

  • Sorry but that's not correct. The page you linked to is for HE-AAC and specifically says not to be confused with MPEG-4 SLS. Also, "AAC - MPEG-4 part3" just refers to standard AAC compression placed into an mpeg-4 container, not MPEG-4 SLS. The actual MPEG-4 SLS wikipedia page doesn't list any compatible software players, just information on licensing the codec.
    – einsteinx2
    Commented Mar 15, 2012 at 21:49

This is the only one I could find, I'm interested in converting my CD collection to MPEG-4 SLS / HD-AAC and it's frustrating this $400+ software is the only product I could find. I don't need all the other stuff this software can do, so it's costly to use this. http://www.sonnoxplugins.com/pub/plugins/products/pro-codec.htm

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