Herbie Hancock admits he would get so wrapped up in the music itself that he never paid any attention to the lyrics when interpreting songs, even on his Grammy-winning album "Gershwin's World."

But the jazz pianist's outlook changed when he recorded an album of songs by Joni Mitchell, his longtime friend who shares his penchant for genre-bending musical adventures.

Hancock spent months working with co-producer Larry Klein, Mitchell's ex-husband and longtime musical partner, analyzing the lyrics and choosing the songs for his new album, "River: The Joni Letters." He even typed out the texts and discussed them with his fellow musicians before recording each track — something he had never done before in the studio.

"It's a territory that I never really explored in the past ... but knowing that Joni's music really grows out of the lyrics, I was determined ... to do everything I could to help ensure that the lyrics were the driving force," said the 67-year-old Hancock, by phone from Tokyo where he was touring with an all-star quartet of fellow Miles Davis alumni — saxophonist Wayne Shorter, bassist Ron Carter and drummer Jack DeJohnette.

"I started playing piano when I was 7 ... and I never looked at the lyrics," said Hancock. "It's very typical of jazz instrumentalists. We're so dazzled by melody, harmony, textures ... that even when I hear a vocal and it's in English, it might as well be in Polish."

A year ago, Hancock eagerly embraced the suggestion of Dahlia Ambach-Caplin, director of A&R at Verve Records, that he do an album of Mitchell's music given their long-standing friendship and mutual respect.

NEW TERRITORY

Hancock and Mitchell have appeared on each other's records since 1979, when the singer-songwriter invited him and Shorter to record the album "Mingus," on which she wrote lyrics to tunes composed for her by legendary jazz bassist Charles Mingus shortly before his death from Lou Gehrig's disease.

At the time, both were exploring new musical territory. Hancock had angered jazz purists by venturing into electronic jazz-funk with his Headhunters band, while Mitchell had upset her fans by moving beyond her pop-folk-rock blend into jazz and world music starting with her 1975 album "The Hissing of Summer Lawns."

"We have the same problem from two different approaches," said Mitchell, who joined Han-cock at a luncheon with several writers at a Manhattan hotel in late September, a day after her new album "Shine" and Hancock's "River" were released. "He was going too far into pop and I was going too far into jazz. They accused him of commercialism and me like if you do that we're going to lose sales.

"I guess Herbie found this challenging to do my music. Harmonically it's wide like jazz, so you got a lot of freedom for choice of notes ... but it's not within the laws of jazz."

Hancock says it's clear from Mitchell's music that she was "exposed to jazz early on." That's why he included two jazz instrumentals that influenced her development on "River": Duke Ellington's "Solitude," which Billie Holiday sang, and Shorter's "Nefertiti," which he and the saxophonist recorded with trumpeter Davis' quintet in 1967.

JAZZ PERSPECTIVE

Hancock and Klein were determined not to make another hodgepodge tribute album. Instead, "River" reflects Hancock's personal look at Mitchell's music from his own jazz perspective. The pianist put together a stellar acoustic jazz quintet with Shorter, bassist Dave Holland, drummer Vinnie Colaiuta and guitarist Lionel Loueke who play on nearly all the 10 tracks.

But he decided he didn't want to use any traditional jazz singers, but rather vocalists who could approach jazz from their own perspective, including Norah Jones ("Court and Spark"), Corinne Bailey Rae ("River") and the Brazilian Luciana Souza ("Amelia"). Mitchell's poet mentor, Leonard Cohen, closes the album with a gravelly recitation of "The Jungle Line," her surrealistic look at a jazz club, to the sparse accompaniment of Hancock's lone piano.

"I always like to have something that's not expected on my records," Hancock said.

Perhaps the most surprising vocal is Tina Turner's restrained performance on "Edith and the Kingpin," about the underworld denizens of a bar.

"There's a kind of purity and subtlety in the way she's singing on 'Edith and the Kingpin' that we're not used to hearing from her," said Hancock. "I would say that she's reinventing herself as a new Tina."

GREAT RESPECT

Hancock didn't advise Mitchell of his plans for the album until last January when he took part in the Toronto ceremony inducting her into the Canadian Songwriters Hall of Fame. Mitchell decided to contribute to the album by singing "Tea Leaf Prophecy," a portrait of her parents' World War II courtship, in tribute to her mother, Myrtle Anderson, who died in March at age 95.

Hancock was struck by how different this version was from Mitchell's original recording of the song on the 1988 album "Chalk Mark In a Rainstorm."

"Joni's one of the greatest jazz singers that I've ever heard — it's her phrasing, choice of notes and the improvisatory choices she makes. I mean, she explores," said Hancock, who also had Mitchell sing several tracks on his 1998 "Gershwin's World" CD.

In November, Hancock will perform material from "River" on a West Coast tour with his own quartet — with Colaiuta, Loueke and bassist Nathan East — and Sonya Kitchell, an 18-year-old blond singer-songwriter-guitarist who could be typecast as the young Mitchell in a biopic.

Hancock says that doing the CD, and delving more deeply into her lyrics, has only increased his respect for Mitchell.

"She has the courage to express what she really feels and believes in," he said. "She's not afraid to openly voice her viewpoint on the crises of the era ... and she does it in such a beautiful and imaginative way."