As a musician, Mr. Duke made forays into the avant-garde rock of Zappa, Brazilian jazz and urban funk. His long string of recording credits included keyboard work on Jackson’s 1979 “Off the Wall” album and records by jazz saxophonist Sonny Rollins and trumpeter Davis.
In the 1960s, Mr. Duke studied trombone and string bass at the San Francisco Conservatory of Music while playing piano in his own jazz trio in clubs at night. The group’s engagements included a stint as the house band with singer Al Jarreau at San Francisco’s Half Note club.
Mr. Duke also struck up a partnership with French violinist Jean-Luc Ponty, and the two recorded an album in 1969 and gave a series of performances in the San Francisco area that drew the attention of Zappa and the jazz saxophonist Julian “Cannonball” Adderley.
In the next decade, Mr. Duke divided his time between playing organ and synthesizer on tours with Zappa’s rock band, the Mothers of Invention, and playing electric piano in Adderley’s jazz group. Starting in 1976, he co-led a jazz fusion group with drummer Billy Cobham, a noted Davis collaborator.
In the studio, Zappa pushed Mr. Duke to use the keyboard synthesizer in new ways, even to imitate the string bends of a guitarist.
“Bend notes! I’m a piano player,” he once said. “Now I can be like [blues guitarist] Johnny ‘Guitar’ Watson. I could play the blues on a synthesizer. I said, that’s it!”
Mr. Duke appeared on nine albums by Adderley and at least 13 by Zappa, including “Roxy & Elsewhere” (1974). When he wasn’t touring with Zappa, Adderley or Cobham, Mr. Duke led and recorded prolifically with his own fusion band.
Mr. Duke said he had wearied of fusion by the late 1970s.
“I felt that had I played as many notes as I could play,” he later told The Washington Post. “I was tired of looking out from the stage and seeing mostly men. . . . The fusion shows attracted mostly men, because it’s male-driven music. Ladies like softer, groove-oriented music. I was wondering if I could draw a different kind of audience with a different kind of music.
“The turning point happened right there in Washington, at the old Cellar Door,” he said. “Ndugu [drummer Leon Chancler] started playing this beat and I liked it so much that I told Byron [bassist Byron Miller] to start playing along to it while I added something on top. We called it ‘Reach for It’ and it became the title track of our next album.”
“Reach for It,” a dance groove that could have come from George Clinton’s Parliament, reached No. 2 on the Billboard rhythm-and-blues charts in 1978 and considerably broadened Mr. Duke’s audience — even as it alienated more than a few of his fusion fans.