There were many Frank Zappas: guitar virtuoso, studio tinkerer, writer of raunchy rock songs. But at his core, he was a legitimate composer, with ideas often too massive for a typical band format.

Fittingly, Zappa made his final formal stage appearance as a conductor, leading the 25-piece Ensemble Modern during a performance in September 1992.

By that point, Zappa had firmly left the rock world behind him: He’d staged one final tour in 1988 and, after being diagnosed with terminal prostate cancer two years later, focused on writing for orchestra and early sampling workstation the Synclavier. (He did play the guitar — with his typically inspired, cinematic style — onstage twice in 1991, during a pair of guest spots in Prague and Budapest)

While rumors of Zappa’s cancer diagnosis had been circulating in the media, the news wasn’t publicly acknowledged until late 1991, when he failed to make a planned appearance at the “Zappa’s Universe” tribute concerts. According to Barry Miles’ 2005 book, Zappa: An Autobiography, Zappa’s daughter Moon told reporters at a New York press conference, “Up until the last minute we were still hoping he would feel well enough to get on a plane and come here. There are occasional periods when he’s not feeling as well, and it’s unfortunate it happened to coincide with this event. He’s thrilled people are performing his music.”

Listen to Frank Zappa and Ensemble Modern’s Version of ‘Uncle Meat’

Despite his failing health, Zappa was also thrilled to work with the Ensemble Modern, finally realizing the full potential of his orchestral ideas. The collaboration began after he was selected as a featured composer for the 1992 Frankfurt Festival; seeking a group of musicians versatile — and, of course, unconventional — enough to handle his ideas, Zappa eventually met with the Ensemble and found instant chemistry. The group traveled to Los Angeles that summer and played for Zappa individually, allowing him to assess their skills and record samples of their playing, which he later arranged with the Synclavier.

“One of the things I like about the Ensemble Modern is that they’re interested in sound just for its own sake,” he told the Los Angeles Times. “At one rehearsal, one of the horn players picked his horn up off the floor, and it scraped and made a noise. And I said, ‘Do it again,’ and the next thing you know, we had the entire brass section taking their instruments and scraping the bells back and forth across the floor, making this grinding, grunting sound. Just try to imagine that at a Hollywood recording session.”

After further rehearsals in Germany, Zappa and the Ensemble created a 90-minute repertoire that blended newly composed material (like the stately string quartet piece “None of the Above”) with revamped versions of old rock staples (“Pound for a Brown,” “Uncle Meat”) and recent Synclavier pieces (“G-Spot Tornado”). They recruited an outside conductor, Peter Rundel, along with the Canadian dance company La La La Human Steps — a formidable presentation for a run of concerts in Frankfurt, Berlin and Vienna.

Watch Frank Zappa Conduct ‘G-Spot Tornado’

Zappa was riveted by the rehearsals but was only able to attend two of the actual performances, the first and third at Frankfurt’s regal Alte Oper. He did, however, manage to conduct “G-Spot Tornado” on opening night — while soaking in a bit of the crowd’s rabid enthusiasm. “There’s no accounting for taste,” he jokingly told Today in 1993, reflecting on the reported 20-minute standing ovation. “I was sick, so it was hard to be truly thrilled, but I was happy they did that rather than throw things at the stage.”

In retrospect, it’s sad to watch the footage of Zappa conducting — understanding the weight of his pain, realizing he’d be around for barely one more year. (An album recording of the concerts was released under the name The Yellow Shark in November 1992, one month before his death.)

But the sight is also inspiring: Here he is, stoic and slightly mischievous, guiding this massive band through a swirl of technicolor sound. It’s Zappa at his purest.