What’s a band without musicians?

That sounds like a paradox or a riddle. But by their sixth album, Steely Dan had fired everyone in the band, leaving only a songwriter and a producer. The resulting record, running about 40 minutes, was just seven tracks, two of which ran over seven and a half minutes long, largely made of unusual rhythms, dense chords, and uncommon narratives about drunk newscasters and orientalist wet dreams. A full LP of music for a band without a band.

It also went five-times platinum in the states. This landmark work of esoterica came to hold an unreachable standard for sonics; the only Grammy it won the year of its release in 1977 was for engineering. The impossible detail applied to Aja shimmered off the album’s intricate chordal and rhythmic superstructures, sparkled against the masterful and famously labored performances of the best musicians the day had to offer: Wayne Shorter, recently of the Miles Davis Quintet; Bernard “Pretty” Purdy and Steve Gadd; Larry Carlton, fresh off several years with Joni Mitchell on some of her best albums. Hired guns; mercenaries.

Aja is remembered, and often maligned, for its emphasis on the precision of its recording. Despite its commercial success, it’s often called niche, given the peculiarities of its style. Even given the popularity of jazz and jazz fusion in its own right and in pop music, Aja can either be called antiquarian or hidebound in its sound, or, alternatively, as Rolling Stone wrote, containing “some of the few important stylistic innovations in pop music in the past decade.”

However that debate shakes out, it's clear that Aja is the weathervane for the most important change music ever underwent: its industrialization. What makes Aja anathema to so many was the way it was led by engineering, facilitated by recording technology, and, most importantly, defined by production. Four decades on from this album, popular music is, too, largely defined by production, and myriad genres have come into being thanks to the possibilities it created. Considered an indulgence in its time, Aja indicated the future.

Recorded music itself is a creation of technological innovation, but it wasn’t until the massive boom in research, development, and productive capacity during the Second World War that instruments like the electric guitar, or the amplifier, could be mass produced at a low enough cost to meet a consumer market newly enriched by the global growth following the war. Fender began selling guitars in 1946, which fueled a boom of guitar-centric bands in clubs for decades to come. Suddenly it was possible for more people to play to more people in more places, and make a very different noise while doing it. Combine this with the proliferation of mass media in radio, records, and television, and creating and consuming music was suddenly far cheaper and more widespread than before. This changed how music sounded.

The advent of radio, and, as a result, of mass-market popular music, had dramatic effects on music as a profession. This low bar to access effectively amateurized the work of performance, and at the same time, created an entirely new trade around its recording and delivery. Recording engineers, in their early incarnations, were more purely engineers than anything else: Paul McCartney recounts how, when creating the Beatles’ 1969 album Abbey Road at the studios of the same name, engineers employed at the site were required to wear white lab coats on the premises.

That juxtaposition, between four self-taught musicians reared in clubs with mass-produced electric instruments playing songs they wrote and performed, and uniformed engineers working in a studio setting Winston Churchill said made him feel like he was in a hospital, describes the inexorable change music would undergo and never return from. In effect, because becoming a musical performer had become financially attainable for most individuals, but the costs to recording and distributing that music remained accessible to only those with requisite investment, music largely became professionalized around production. For all but the most successful songwriters and performers, the money wasn’t in making music, it was in making records.

The Beatles are celebrated for using the studio as an instrument, particularly after they stopped touring in 1966. Steely Dan took this idea that much further. After a number of years of commercial success, the band’s songwriter, Donald Fagen, and producer, Walter Becker, began to find the conventional ensemble context unsatisfactory. So, in 1974, they fired the other three members of the band and scaled their touring back significantly to focus on making records. With each album they made following—Katy Lied, then The Royal Scam—the “band” trended further toward the AM jazz of Fagen’s songwriting and the flossed twinkle of Becker’s production. This focus on sound and style translated to a rigor for performance, which was borne out in the ablest hands music’s pool of session musicians had to offer, with unlimited takes at their disposal.

Which brings us to the legend and spectacle of Aja, which stands with Abbey Road on the famous end (and perhaps Chinese Democracy on the more infamous end) in music’s new lore of the studio. With endless time, limitless talent, and a new arsenal of recording tools, Steely Dan made it possible to make a record with impossible exactitude. “Up on the hill,” Fagen sings on the title track, “they've got time to burn.” That’s part of why so many people hated it: it was stylistically and performatively implausible, made in and for the recorded environment rather than the pub or rehearsal space, which, prior to that, was the only place music could have been made. It is the day of the expanding man.

This is to say nothing of the songwriting itself, which is wonderful. But it’s the jazz-heads and audiophiles who extol the drama of “Deacon Blues,” or the Odyssean “Home At Last.” To so many listeners, the ballistic upper partials that festoon Gadd’s fractalizing tumult on the album’s title track, set in glinting clarity by Becker's production, are just fake—unreal in the sense that they couldn’t have played to a club. And that’s the point, frankly: This is the beginning of what’s possible beyond the physical realities of music, music that is an abstraction of itself, primarily. It’s music like you’d imagine music if you weren’t really hearing it, but remember how good it might have been if your focus was only on it. And, in that way, you can hear it better than maybe you ever had before. “The essence of true romance,” if you will.

The business of music continued to shift to its production and dissemination in the decades following, and that largely stands today. Max Martin, a producer, is among the most successful and influential songwriters in generations; Rihanna’s songwriting summits are storied; Some of the most celebrated music of our time is the realization of production; Rap and electronic music are defined by what an individual can do in the studio, not what happens beyond it.

This is, of course, a tragedy to those who believe music is pure in live performance and most honest when produced “organically.” The cool control of Aja seems an affront on music like it was. But music isn’t what it was, it has never been. The unreality of Steely Dan is like art to art: Tom Scott’s jubilant saxophone solo on “Black Cow,” Michael McDonald’s clarion background vocals on “Peg,” Chuck Rainey’s silvery bassline on “Josie,” each are perfect in their realization, as things never are. “When you smile for the camera,” they sing, “I know I'll love you better.”

—Charlie Kaplan