When Herbie Hancock releasedPossibilities(2005), a collaborative effort that paired the great pianist and composer with a group of pop and rock stocks from the world over, it was obvious the restless master was entering a new phase of his long career. In that context, River: The Joni Letters makes perfect sense. Hancock and his fine band --Lionel Loueke(guitar),Wayne Shorter(soprano and tenor saxophones),Dave Holland(bass),Vinnie Colaiuta(drums) -- prepare a series of instrumentals and vocal interpretations of the songs ofJoni Mitchell. The vocalists here include those who were inspired byMitchell, namelyNorah Jones,Corinne Bailey Rae, andMitchellherself on one number (her own recording,Shine, was released on the same day), and some of her peers in the pop world, includingTina TurnerandLeonard Cohen. 　　Cohen's connection to the songwriter is direct in that they are both Canadians and both came up playing clubs and venues in the then new "folk" scene. But Hancock understands something implicit aboutMitchell: she was never -- ever -- a folksinger. Her compositions have always walked wildly adventurous rhythmic and harmonic terrain. Indeed, she has played with jazz musicians solidly since the 1970s, beginning with the L.A. record,The Hissing of Summer Lawns, and toured with jazz groups, including the all-star band assembled forShadows and Lightthat includedPat Metheny,Jaco Pastorius,Lyle Mays,Don Alias, andMichael Brecker(Shorterplayed on a number of those dates as well). Indeed, whenMitchellasked no less thanRobbie Robertsonandthe Bandto back her on a tour, they had to excuse themselves because they simply couldn't find a way to play behind her. The material here doesn't walk the line between pop and jazz -- something Hancock is very comfortable doing. This is a jazz record with vocals. The album's ten tracks are, for the most part, programmed for a vocal tune, followed by an instrumental. This holds true with only one exception in that the disc's first two songs are vocals. First there's the lovely, spooky, smoky "Court and Spark," sung byJones, followed immediately by the ethereal yet from-the-gut version of "Edith and the Kingpin," sung byTurner(it should be noted here that she is in fine voice, since she hadn't been heard from in quite a while). In this latter cut, it's a testament to the singer, the writer, and Hancock, how deeply soulful this performance is. 　　Turneris one of the great soul singers, but this ballad lends itself to another kind of reading and is therefore radically reinterpreted here with ...