How are music downloads 'upsampled'?


When I download music from iTunes, it comes in at maybe a 4mb file. When I change it to an 'Apple Lossless' file, it becomes a 20mb file. Where does that new data come from?
hi_end
New data can not be created. Upsampling simply uses an algorithm to flll in additional data points. It is simply an educated guess.
Alan
Arh is correct, there is no sonic advantage in converting from an iTunes
native file to Apple Lossless. When the data was stripped away to create a
smaller file there is no way to get back the original fidelity by converting
to a different format and larger file.
No use in converting mp3 to apple lossless just uses up more hard drive space. You could even go all out and convert to 24/192. I have to wonder if that is all they have done with some of the hi Rez downloads they are selling now. I have closely compared some and cannot hear a bit of difference. Just another way for the record companies to try and screw us.