by William Ruhlmann The informal title says a great deal about the contents of The Mozart Sessions, which could have been called Concerti for Piano and Orchestra, Nos. 23 and 20 , since that is, for the most part, what it is. But of course the conductors, vocalist Bobby McFerrin and jazz keyboard player Chick Corea , are not your average classical musicians. Nor is there any doubt about the non-traditional nature of the recording, when it starts with McFerrin's patented improvisational vocals followed by Corea's piano inventions under the title "Prelude." So, for a start, purists should be warned away. On the other hand, the more adventurous may be slightly disappointed, since after they get the preliminaries out of the way, McFerrin and Corea , aided and abetted by the St. Paul Chamber Orchestra , turn in pleasant but unexceptional readings of the concerti, with Corea especially eschewing any attempt at dazzle in what are usually sho...