Over at the O’Reilly website is an article entitled How to Convert Digital Audio Files
Here’s the quote
There are so many types of audio files out there that it’s all too easy to end up with the wrong one. Maybe you converted your CD collection to Real Audio or WMA and now want to convert the songs to a nonproprietary format, such as MP3, so you can play them with iTunes. Or maybe you purchased songs in a copy-protected AAC format from the iTunes Music Store and need to convert them to MP3 so they’ll work in your portable player, handheld computer, home network, or competing jukebox program, such as Musicmatch Jukebox.
It’s a good place to start trying to make sense of the alphabet soup that is digital music formats.