Steely Dan released Aja on September 23, 1977, and within three weeks it had reached the top five of the Billboard Top LPs chart on its way to number three. That sounds like a standard commercial success story. It was anything but. Aja was seven tracks long, two of them running past seven and a half minutes, built from jazz-based chord progressions, dense harmonic structures, and the contributions of nearly forty session musicians assembled and auditioned with something closer to obsession than production. The album did not soften its ambitions to reach a mass audience. The mass audience came to it. That is the rarer thing, and understanding why it happened tells you something important about what FM radio had become by 1977, what listeners were actually ready to absorb, and what the crossing cost.

The recording sessions ran from January to July 1977, primarily at a small studio on Hollywood Boulevard called Producers' Workshop, with overdubs handled by engineer Roger Nichols at Village Recorders in Los Angeles. Engineer Bill Schnee tracked most of the sessions, with Al Schmitt and Elliot Scheiner also contributing. Producer Gary Katz, who had worked with Walter Becker and Donald Fagen since the band's formation, presided over a process that was famously and deliberately punishing. Each song was recorded with multiple configurations of players; the duo filtered through dozens of rejected guitar solos on the infectious "Peg" before settling on Jay Graydon's take. On "Deacon Blues," Becker himself ended up playing bass. The drummer situation alone reads like a casting call for a film: Steve Gadd, Bernard Purdie, Rick Marotta, and others all rotated through, with Gadd's explosive, structurally complex performance on the eight-minute title track standing as perhaps the most celebrated drum performance on any record of the era. Purdie, whose famous shuffle had been a session staple for years, anchored the funky, unhurried "Home at Last." The musicians on the record were not a band. They were a roster, assembled track by track, part by part, to serve specific compositional needs.

The specifics of who played what on Aja are worth naming because they reveal exactly what kind of record this was. Wayne Shorter, recently of the Miles Davis Quintet, played the stately, rhapsodic saxophone solo on the title track, a solo the liner notes — written pseudonymously by Becker and Fagen themselves — described as "descending gracefully into a recapitulation of the vocal theme." Pete Christlieb, whose playing Becker and Fagen had noticed on The Tonight Show Starring Johnny Carson, was brought in for "Deacon Blues." Guitarist Larry Carlton, fresh from years of session work with Joni Mitchell, contributed to the album's guitar arrangements. Tom Scott's saxophone solo on "Black Cow" gave the album's opening track its jubilant, slightly sideways momentum. Michael McDonald sang backing vocals on "Peg," his voice adding the bright, clarion harmonic texture that helped push the single to number eleven on the Hot 100. Chuck Rainey's bass was the one constant across the sessions, his silvery line on "Josie" and slap-bass harmonics on "Peg" providing the rhythmic spine that held the album's more elaborate structures in place. Every one of these contributions was chosen, rejected, revised, or replaced until Becker and Fagen were satisfied. Becker later called the album "dangerously ambitious." He was not wrong, and he said it approvingly.

The crossover question is this: why did an album this demanding, this unapologetically jazz-inflected, this indifferent to the conventions of rock radio, become Steely Dan's fastest-selling record and one of the first albums to receive the then-new RIAA Platinum certification? Part of the answer is that FM radio had spent the early and mid-1970s training its audience to listen to album tracks rather than singles, to tolerate longer forms and more sophisticated production, to treat the listening experience as something worth paying attention to. By 1977, that audience was ready for Aja even if it did not know it yet. Billboard called the album the year's "most polished," and the NME called it "simply the finest and most sophisticated and intelligent rock album to be released this year." ABC Records spent $275,000 on television advertisements for the album in the summer of 1978, and FM stations were playing all seven tracks in rotation. The record was everywhere. But it was everywhere on its own terms. Becker and Fagen had not written shorter songs or simpler chord changes or more radio-friendly arrangements. They had simply made the record they wanted to make, and the infrastructure of FM radio, built over the previous decade, turned out to be exactly the right delivery mechanism for it.

What the crossing cost is the part that tends to get left out of the celebration. Aja was nominated for Album of the Year at the 1978 Grammys, competing against Fleetwood Mac's Rumours and the Eagles' Hotel California. It did not win that award. It won Best Engineered Recording, Non-Classical, for the work of Nichols, Schmitt, Scheiner, and Schnee. That Grammy, for engineering rather than songwriting or performance, is its own kind of statement about how the industry understood the album. The record was acknowledged as a technical achievement before it was acknowledged as an artistic one. And the creative cost was steeper still. Becker later admitted that the album had been "dangerously ambitious," and the three years it took to complete its follow-up, Gaucho, bore that out. The perfectionism that made Aja possible was also what made it nearly impossible to follow. Steely Dan broke up in 1981, not long after Gaucho arrived. The band that had spent seven albums refusing to tour, refusing to compromise, refusing to simplify, had finally been consumed by the very standards it had set.

The Grammy Hall of Fame inducted Aja in 2003, twenty-six years after its release. That gap is instructive. The album's reputation grew in the decades after it arrived, not because listeners came to understand it better but because the recorded music culture it helped create eventually caught up to what it had proposed. The idea that a record could be made with unlimited takes, rotating casts of the finest available musicians, and a standard of sonic clarity that bordered on the clinical, and that such a record could also be warm, melodically generous, and genuinely pleasurable, was not obvious in 1977. Aja made it obvious. "Peg" still sounds like a pop song. "Deacon Blues" still sounds like a jazz ballad for people who have never called themselves jazz listeners. The title track still sounds like something assembled from pieces of other songs, because it was, and the seams are invisible. That is the craft. The crossover was real, and it was permanent, and it happened because Becker and Fagen refused to meet the market halfway.