If were talking about study i believe the music needs to be interesting enough in the background that it can be played over and over again to keep you awake but soft enough not to get in the way by being a distraction. Since I do on the average about 15 hours of study per week i usually use the following selections which have no vocals and no horns. ( Except for a few selections on the (Michel Colombier “ Old fool back on earth) Double album.

Horns like vocals grab your attention and for study you don't want that. If you have iTunes i believe you can preview some of these CD's. Let me know what you think.

Michel Colombier “ Old fool back on earth
Andreas Vollenweider (Caverna Magica Under the Tree)
Ramsey Lewis Maiden Voyage
Ramsey Lewis Ivory Pryamid
Ramsey lewis Sky Island

__________________
"What you hear in a great jazz band is the sound of democracy. “The jazz band works best when participation is shaped by intelligent communication.”
Harmony happens whenever different parts get to form a whole by means of congruity, concord, symetry, consistency, conformity, correspondence, agreement, accord, unity, consonance…….