Jazz pianist Herbie Hancock, right, recently recorded an album of songs by Joni Mitchell (right), a friend who shares his penchant for genre-bending musical adventures.

New York ? 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 old 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, in a telephone interview 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,” Hancock said. “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.

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 the black-clad Hancock 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 both released. “He was going too far into pop, and I was going too far into jazz.”

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. 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. … And so as a humanitarian, Joni Mitchell really reflects her belief in the dignity of human life and its relationship to our environment.”