ATRAC Advanced Lossless (AAL) is the latest update to the codec family. It can provide compression for a CD music source at approximately 30–80% of the original size without any quality loss.
ATRAC Advanced Lossless provides "scalable" compression; it records a lossy ATRAC3 or ATRAC3plus stream, and supplements it, in the same file, with a stream of correction information that allows the original signal to be reproduced, if desired. A player/decoder can extract and use just the ATRAC3 or ATRAC3plus data, or it can combine that with the correction stream to perfectly reproduce the original audio information. This allows the file to be decoded as either lossless or lossy. It is implemented in such a way that allows the file size to be smaller than uncompressed or compressed versions of the same file. Benefits of scalable compression include providing backward compatibility, such that older devices that are not AAL-aware can still have the ATRAC3 stream available for playback without understanding the AAL format, and faster transfer speed between portable audio devices and PC.
ATRAC Advanced Lossless is widely supported in older Walkman players and SonicStage version 4 or later. Sonic Stage 4 allows download of ATRAC Advanced Lossless to Minidisc Players, PlayStation Portable, and PlayStation 3. Recent Walkman players do not support ATRAC Advanced Lossless/ATRAC. Sony has all but dropped the ATRAC related codecs in the USA and Europe and their SonicStage powered 'Connect' Music Service (Sony's equivalent of iTunes) on 31 March 2008. However, it is being continued in Japan and various other countries.
Read more about this topic: Adaptive Transform Acoustic Coding
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