Rsbeck: The same way data compression works with other computer files: zip, stuffit, whatever. You can compress a file on your computer, de-compress it, and get back the exact file, bit for bit. Apple Lossless works the same way.
That's distinct from "lossy" compression, like AAC and MP3, which aren't reversible. What you take out, you can't put back in. But if you start by taking out the things people can't hear anyway, and then move to the things that are very hard to hear or not very noticeable, the effect is relatively benign.
