One of the best compliments you can give a group is that its music makes you stop what you're doing and pay attention. To this day, I find that instrumentals work better than vocals for one's comprehension while reading. This was the case when studying for tests in school, and it's still the case when trying to concentrate on a book.
For background music, I find that an album of consistent, contemplative instrumentals, such as Liz Story's "Solid Colors" or George Winston's "Autumn," works best. You're able to appreciate the piano arrangements while comprehending what you're reading.
Using vocals as your background music, however, challenges you not to pay attention to the lyrics or start singing along. I've found I've had to read some of the same material at least three times to remember it when I've listened to well-sung vocals. If I don't stop and actually listen to the music, I'll find myself thinking later, "How much of a tax increase did that report say it was going to be? When is that road construction going to start, again? What's tomorrow's predicted high temperature? I know I just read it, but I've forgotten it." Such was the case recently when I listened to the "40 Days" CD by The Wailin' Jennys. Throughout all of their incarnations, The Wailin' Jennys have maintained a great blend of moving harmonies. Try catching up on the news while listening to such standout tracks as "One Voice" or "Something To Hold Onto." Your ears will likely tell you to give your full attention to Cara, Nicky, and Ruth's voices.
I went back to the news as I listened to various violin instrumentals by Annbjorg Lien. I can still remember the energetic melody of "Iriandia" while also retaining that tomorrow's predicted high temperature is 78 degrees, and no rain is expected.