Some friends were telling me about problems putting music from the iTunes music store on their Android phones. I realized the problem was most likely old tracks protected with DRM (Digital Rights Management). They didn’t know that Apple had stopped using DRM and they could get new DRM-free copies of their music.
Here’s how to remove the DRM from old iTunes music purchases. This is the official Apple way, which involves buying an “upgrade”. There are other tools you can find that will remove the DRM without the upgrade. I haven’t tried any of those.
This page gives all the details. The short version is that in 2009 Apple made “iTunes Plus” versions of all their music available. This is what you have been getting since then. You can upgrade your old tracks to iTunes Plus. This gives you DRM-free tracks and improved sound quality (they re-encoded the tracks at twice the previous bit rate). The cost is $0.30/track or 30% of the album cost.
This link will open iTunes and show the old tracks that you can upgrade and how much it costs. I tried it myself and saw this in iTunes:
The tracks are still in AAC format (not MP3) so you might want to verify that your music players support 256 kbps AAC before plumping for the upgrade. Or just try one track first to see if it works.