HT1351: iTunes: Syncing media content to iPodLearn about iTunes: Syncing media content to iPod
Currently Being ModeratedAug 3, 2013 1:39 PM (in response to cretali)
If the songs on the iPod are not in your Mac's iTunes library, and you told iTunes to sync an empty (or different) iTunes library to the iPod, the songs that were on the iPod are gone. You can't get them back.
If the songs came from music CDs, you can re-rip them into your current iTunes library. If you purchased any of the songs from the iTunes Store, you can re-download previous purchases from the iTunes Store Purchased screen, at no cost.