Considering their primary function is for making calls I didn't expect much in terms of SQ with the built-in music player. Although they sound decent with earphones, it was just horrible when I tried hooking my cell phone directly to my car amp. Sounded like I was inside of tin can. The small usb thumb drive mp3 player I tried wasn't any better. I don't have an ipod or any of the other higher end mp3 players so I couldn't test those. I'd assume they'll be better but still far from a quality headunit.