Q: My songs in iTunes (Mac of course), all from my own CDs, are in AAC format. When I burn them onto an Audio CD, for use in a normal non-MP3 CD player, they are converted back into uncompressed audio. Are any of the original frequencies etc from the original CD somehow restored when the AAC tracks are burnt back into an audio CD? Is the situation the same if one uses Roxio’s Toast software?
A: Unfortunately, the “lossy” nature of AAC, MP3, and many other compression schemes is permanent – no fidelity can be restored when the audio is transformed back into CD format. These compression schemes are efficient (producing small audio files) in part because they permanently rid themselves of many parts of the audio stream that aren’t essential.
“Lossless” audio compression schemes are different. They’re not nearly as efficient, producing much bigger files, because they behave like a Zip file in that they only compress the audio data, not removing any content. These files, when you listen to them or burn them onto an audio CD, uncompress themselves to restore all of the original audio fidelity.