The best music, regardless of its type or its hometown, is usually created by the musician who is not known by many people to be one, for whom being artistically expressive is an escape from the daily grind rather than the grind itself. For this artist, and for those who love his art, a dream is more fruitful than a dream come true.

This idea is rooted especially deep in American popular music because so much of it has blossomed from the black music made in the early-to-mid 20th century South, where there was an inordinate amount of dreaming going on. Blues and gospel, which grew in the Delta among the cotton stalks that sustained the land, rang with pain and longing, but also with faith and aspiration.

Both art and commerce impelled two white siblings from Memphis, Jim Stewart and Estelle Axton, to found Stax Records in 1957. Their dream was simply to record country tunes, but the working-class kids who streamed through their doors had other ideas. Through the two decades that followed, their Stax label, whose history will be on-screen in a PBS documentary airing tomorrow called “Respect Yourself: The Stax Records Story,” would rise to iconic heights and sink to shocking lows in a constant struggle to stay afloat in the burgeoning music industry. Along the way, it would also hold a kind of musical mirror, often for better and sometimes for worse, to the tectonic racial and social shifts that shook the country.

First came the music. Mr. Stewart and Ms. Axton were an enlightened pair, and they operated their studio with an open-door policy — if you were talented and you could find your way to the corner of McLemore Avenue and College Street, then you could make a record with Stax. The first to arrive were local black kids with nothing to lose and the blueprints for soul music — the melding of blues, gospel, and jazz — in their hands. They were followed in short order by local white kids, who had been thunderstruck only a few years before by the collision of black and white music that was pioneered by Memphis’s own Sun Records, which had produced Ike Turner, Elvis Presley, Howlin’ Wolf, and Jerry Lee Lewis in the mid-’50s. To hear PBS tell it, Stax Records was the Garden of Eden in terms of its disregard for Jim Crow and its portentous fusion of American styles. The total omission of Sun Records’ momentous effect on the young white population is all the more glaring in “Respect Yourself” since Sun was literally walking distance from Stax.

Between 1958 and 1966, Stax introduced the Mar Keys, William Bell, Otis Redding, Isaac Hayes, and Booker T. & the MGs. The last of these was an instrumental foursome, composed of two blacks and two whites, whose sound, a hipshaking blend of electric keyboards and bright horns, exemplified the southern soul style for which Stax would become famous — so much so that the MGs became the Stax house band and the embodiment of what popular music could be.

According to the various musicians and engineers interviewed in “Respect Yourself” who were there, the issue of race was moot within the sound-proof walls of the studio during the early days. Viewers may rightly wonder how that was so as the civil rights movement gained momentum — not to mention how this groundbreaking music contributed to the climate of change — but they won’t find the answers here. Except, as one musician puts it, “While people fought for integration in the streets, at Stax, race was what you did on your way to the bank.”

As the ’60s progressed, Stax slowly established itelf as an indispensible purveyor of the new soul music. But to watch “Respect Yourself,” you’d hardly know that Detroit’s Motown Records was having greater chart success with more enduring artists, and was providing the nation’s only real model for mainstream, blackowned music production — it even had its own interracial house band.

By the late ’60s, Stax was being run by a former civil rights activist named Al Bell (though it was still owned by Mr. Stewart) and was looking for inroads to white America. Redding’s unforgettable appearance at the 1967 Monterey Pop Festival — alongside Janis Joplin, the Grateful Dead, and The Who, among others — launched the singer and his label into the stratosphere. Redding’s powerhouse vocals and infectious stage presense were impossible to resist. The live footage of Redding, of Sam & Dave, and of the MGs twisting and shouting before throngs of barely contained teenagers lends the documentary its most watchable moments.

Redding provided the soundtrack for the social revolution taking shape under the stewardship of Martin Luther King, Jr. So when Redding’s private plane crashed into a Wisconsin lake on December 10, 1967, the effect on Stax and soul music was much the same as the assasination of Martin Luther King Jr. on the country at large. The label had lost its biggest star, along with his crossover appeal for white rock and folk fans. Not long after, it learned that its distribution deal with Atlantic Records gave the New York label ownership of everything Stax had recorded to date. (“I had not read the fine print in the distribtuion agreement,” Mr. Stewart admits in the film.) Poor financial foresight and the bloated promise of fortune of had corroded the label from the inside out.

As the 1970s dawned, Stax had fallen apart, and much like the wounded black community, the label closed ranks and began to focus exclusively on the black market. Suddenly, integration didn’t seem like the way forward, and Mr. Bell pulled Stax toward the black power movement that was rising from the ashes of the love decade, signing exclusively black artists and advertising for an exclusively black audience. As the documentary points out, it is difficult, even now, to blame him. There was more violence and unrest both inside and outside of Stax Records, but Mr. Bell was not expoliting his community’s sense of anger so much as building his own economic base of black consumers. Further ventures into movie production and sports ownership lifted Stax back into the black, but it also dragged the label away from its original commitment to the music.

Tellingly, the mid-’70s hosted a remarkable resurgence for the label, which, at one point, replaced cotton as the biggest industry in Memphis. But as the money flowed, the egos grew, and the country stumbled forward, the music suffered. So what should be an uplifiting story of Stax’s triumphant return is instead the most tedious portion of this two-hour film. Gold-plated cars took the place of gold records, and a subsequent distribution deal with Clive Davis’s powerful CBS Records, which looked like the final step to salvation until Mr. Davis was fired by CBS, once again left Stax fending off bankruptcy — a fight it would lose in 1976.

By that point, though, the innocence of possibilty that had taken a musical form on one street corner in Memphis had long since died away, taking the ingredients of soul music with it.