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 showcase pieces. The piano work is fluid and the orchestral accompaniment delicate, but the principals seem sufficiently concerned about getting anything wrong not to really take off. At the end, as Corea once again improvises in tandem with McFerrin's voice, one longs for more of their interaction, perhaps in a less restrictive context.