Yeah, apple lossless is apples equivalent of flac. If you're not using high quality headphones (ie new ones) then it's not worth it. It's not really worth it anyway on an ipod anyway imho, but that's up to you. WAV is what cds are and they're not really worth keeping. Lossless formats can be converted back to wav with no loss, so you may aswell keep them. Yeah, they do take up more space (uncompressed). AAC is apple's version of mp3, so yeah, lossy. I think they are better quality for the filesize compared to mp3, there's a lot of comparisons on the net. I personally keep all my music in mp3 though, as it is the set standard and is used by everything. Buy a new mp3 player that doesn't support it and you'd be fucked. Also for stuff like mp3 cds to work in dvds players/cars etc. Watch out not to convert your mp3s to aacs (as itunes can make you do) since this is transcoding and is really bad for quality. This goes for any lossy to lossy. You'll be fine going from a lossless to lossy though. That's one of the reasons for keeping your collection as lossless...you always have the power of converting to anything without transcoding. Also, if you're going to start ripping to mp3, get yourself eac, and use lame (the name of the encoder). It is the standard for top quality mp3s. Here's a tutorial jiGGafellz' Step-by-Step Guide to Secure CD Ripping w/Exact Audio Copy to help you with that. EAC secure rips, and ensures exact copies from your cd. Hope that helps (and hope i've been right). Don't know anything about AIFF though.