Jarrett was sleep-deprived and harried that night, and his mood wasn't helped by the fact that the opera house had supplied a relatively small, poorly tuned piano rather than the Bösendorfer grand that he requested. Even after an emergency tuning, the instrument supposedly sounded like a toy, with shrieking high notes and little projection in the low registers. On the record, having passed through two microphones, the piano has an almost otherworldly sound, like it's five stories high and made of glass. Jarrett plays it harder than he does on his other solo recordings, bashing the keys and keeping largely to the mid-range notes, perhaps out of frustration. "What happened with this piano was that I was forced to play in what was—at the time—a new way," he explained years later. "Somehow I felt I had to bring out whatever qualities this instrument had."

This is all backstory and context, but as an album, The Köln Concert melts context, vaporizes it: Purely as music, it exists outside time and space. It's a perfect product of the shaggy, stoner '70s, but it sounds completely modern right now and will remain so 40 years from now. Like everything ECM releases, it sounds somewhat clinical in a European fashion, but Jarrett's musical imagination is undeniably American, spanning funk, blues, and pop balladry. I agree with Geoff Dyer's assessment that "when Jarrett is at his best, snatches of all kinds of music flow through his work, but there is never any sense of strain, of a conscious effort to combine these disparate influences." This is as close as you'll ever come to actually hearing a genius think. The ideas build and mutate, and Jarrett is such a shockingly talented instrumentalist that there seems to be no distance between his brain and his fingers.

Jarrett has remained uncommonly prolific in the four decades since Köln, though his music has rarely bore any resemblance to it. He continued to play solo improvised concerts for decades, and in the early 1980s founded the Standards Trio with fellow Davis and Lloyd alumnus Jack DeJohnette on drums and Gary Peacock on bass; their body of work, largely drawn from the American songbook, is as respected as any contemporary jazz combo's, and they remain a reliable live draw. But Jarrett's contemporary compositions are rarely so genreless and accessible as his 1975 masterpiece, and his concerts have never regained that group-séance feel. In fact, his prickliness onstage—pausing to lecture audiences on the rudeness of coughing, for example—has become nearly as legendary as his still-inspired playing.

But what a marvelous, bizarre thing that an artist like this can become so popular, even for a moment, embraced by people, like my dad, who barely messed with jazz besides. I first discovered Köln in our basement, among Dad's old LPs, sandwiched among Ten Years After, Grin, and Mountain. I was a young teenager, intrigued by the spare album art and curious as to how Dad could like something so New-Agey. When I listen to it now, I get the same feeling I had the first time: I feel stronger, smarter, more inspired. It works when I'm sad, when I'm joyful, when I'm driving or falling asleep.

In David Foster Wallace's 1989 story "Girl With Curious Hair," the unnamed sociopathic narrator goes with his dirtbag friends to a solo Keith Jarrett concert in the early '80s. The friends drop acid, and one explains that the improvisation "smelled like old velvet in a trunk in an attic, or like vitamins, or medicine, or morning … [It] resembled weak sunlight through ice." That's true enough, but I prefer the brevity of the awful narrator, who's never heard Jarrett's music before and who, sober, declares with great enthusiasm that the show is "punkrock." The Köln Concert will remain ever so.

John Lingan has written for Slate, The New Republic, The Virginia Quarterly Review, and lots of other places. He lives in Maryland, and is on Twitter.

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