Advanced Audio Coding
AAC or 'Advanced Audio Coding' forms part of the latest specifications from the MPEG committee, and is their official successor to the popular MP3 format. As with MP3, the AAC format is an international standard, and is backed by several big-name companies, including Dolby, Sony and Nokia.
With the 13 years that had passed since the creation of the MP3 format, many improvements had been realised leading to a seemingly complex specification with several flavours of AAC available. To potentially add to the confusion, AAC is usually wrapped inside an MP4 container to provide tagging, seeking and possibly other benefits?? For this reason, AAC can also be referred to as MP4 audio..
There are several AAC encoders to choose from, coming from large names such as Apple (iTunes) , Real Networks and Nero AG (Creators of Nero Burning Rom), or the open source FAAC which is analogous to the LAME encoder. AAC is supported on some hardware players, most notably the Apple iPod and some cell phones, and is available in Apple's online store.
In terms of quality, it outperforms MP3 by a nice margin, being on par with Ogg Vorbis, WMA Pro and other modern codecs, and with added SBR coding (HE AAC) it can provide quite high quality at low bitrates.
- An international standard approved by the ISO
- Flexible: supports several sampling rates (8000-96000 Hz), bit depths, and multichannel (up to 48 channels)
- Several implementations, including a free and high quality one (iTunes)
- Reaches transparency in most samples and for most users at around 150kbps
- Part of MPEG-4 specs
- Anyone can create its own implementation (specifications and demo sources available)
- Some portable players support it (Philips Expanium, Apple iPod, cell phones from Nokia)
- Problem cases that trip out all transform codecs
- Heavily patented
- Increased complexity
- AAC comes in different "flavors" (object types: AAC LC, AAC HE, AAC PS etc.). Many (especially portable) players only support LC (at the moment) so you can have files that are valid but your player won't play them.