The idea that you should listen to music while meditating is very common. It probably goes back to seeing meditation as little more than a means of relaxation. Of course meditation does help you to relax, but it goes beyond that and helps us to be more alert and focused. Music is likely to get in the way of that.
If you’re trying to pay attention one-pointedly to your breathing, then you can’t also listen to music. And if you’re trying to listen to music then you can’t fully concentrate on your breathing. Focusing on music is fine, and I wholeheartedly suggest that you try doing that. I also suggest that you try doing it at a time when you’re not meditating.
I’d go further and suggest that listening to music, if done properly, can be a meditation in itself, just as walking or washing the dishes can be. You can take many activities and make them richer and more satisfying by taking more awareness into them. Music, as we’ve seen, is just one example. If you’re going to listen to music as meditation then try not to do anything else at the same time. Don’t work, or read, or balance your checkbook while you’re listening. Just listen to the music. Sit or lie down comfortably, and just pay attention to the music. You’ll probably find that you enjoy it like never before.