Sonnox Fraunhofer Codec Toolbox - Manual (Page 7)

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5 Codec Details
Apple AAC iTunes Plus (Mastered for iTunes) (Mac only)
The addition of the Apple AAC codec allows real-time audition of files produced under the
Mastered for iTunes initiative that are destined for the iTunes store.
This codec is available for Mac computers only. It uses the same Apple codecs and re-samplers
that are used for the current iTunes Catalogue. It very specifically re-samples to 44.1 kHz if
necessary, and encodes as AAC-LC, 256 kbps, variable bit rate and maximum quality, which are
the settings used for the iTunes catalogue. For online audition, the signal is then resampled back
to the host DAW sample rate if necessary.
This option is available only for stereo configuration. There are no options to change the iTunes
codec settings because this would not be representative of the iTunes Plus standard. The Apple
codecs and re-samplers are components of the Mac OSX operating system, so can be upgraded
during an OSX update. On Windows computers, the closest approximation to the iTunes Plus
codec is the Fraunhofer AAC-LC codec set to VBR at 256kbps.
MPEG Surround (Fraunhofer)
MPEG Surround is a feature-rich open standard compression technique for multi-channel audio
signals. Operating on top of any core audio codec – including AAC, HE-AAC and MPEG Layer 2 –
the system provides a comprehensive feature set, including highest surround and stereo audio
quality, in addition to multi-channel support at stereo bit rates.
HD-AAC (Fraunhofer)
The HD-AAC codec from Fraunhofer has a very clever feature; the single compressed lossless file
includes a lossy core channel. It therefore acts as a lossless archival format, a lossless distribution
format for the masters, and a final playback format for both lossless and lossy decoders — and all
of this in a single file.
In the case of HD-AAC playback, if the decoder in your player has full HD-AAC capability, you will
be able to listen to a perfect replication of the original WAV file. However, the same HD-AAC file
will still play through a decoder that doesn’t have HD-AAC capability, and instead you will be
listening to the embedded lossy AAC channel.
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