THE SOUNDTRACK FOR Sweet Sweetback's Baadasssss Song has no wakka-wakka guitars scratching out a funk groove, no cinematically inspired orchestral swells, not even an obligatory car chase score. Instead, you get the eight-minute "Sweetback's Theme" – a raw, lo-fi composition that repeats its saxophone and keyboard riff like a mantra. The song doesn't sound much like "blaxploitation," but then again, before filmmaker Melvin Van Peebles wrote his baadasssss song, there was no blaxploitation sound.

Peebles came to the Bay Area recently to help promote his son Mario's new film, Baadasssss!, a "making of" feature that tells the story of how Peebles put together Sweetback's, arguably one of the most important independent films of the past 30 years. Though the astounding success of Sweetback's established Peebles as an architect of a new black cinema, his contributions to modern black music are far less recognized, despite being just as seminal.

Long before Sweetback's, Peebles had insisted on doing the music for his films, stretching back to 1957 with the short "Three Pickup Men for Herrick." As he told me when I spoke to him, he learned how to score his own films out of "this magical necessity of [having] no money." Lacking funds and formal musical training, Peebles made do with what he had for "Herrick": "I couldn't play any instrument, so I got a harmonica and I got a kazoo. When I wanted something more intricate than my harmonica, I hummed it. If you see 'Herrick,' that's me humming alone because I couldn't do anything better," Peebles said.

By the time he made his 1963 short in Paris, "Cinq cent balles," he had begun to expand his musical horizons. "I had a buddy who knew how to play the violin, so he'd listen to me and then play it on the violin. That was the soundtrack," he explained. Returning to the United States in 1967, Peebles began work on Br'er Soul, an album for A&M that mixed black power-inspired poetry over soul and jazz tracks – two years before the Last Poets and Gil Scott-Heron would follow suit. By then, Peebles had developed a rudimentary system for writing music: "I numbered all the keys on the piano. I'd go one to eight, and someone said, 'Oh, one is middle C.' I didn't know what middle C was. I explained what sounds I had, and they transposed what I had in mind."

When it came time for the music on Sweetback's, Peebles had yet to score the movie when he enlisted the aid of a young Los Angeles soul group led by the boyfriend of one of his production assistants. His name: Maurice White. His band: Earth, Wind and Fire.

In Baadasssss! the moment when Peebles and White meet elicits laughter. As the audience, we get the joke – "This is Earth, Wind and Fire, wow!" – but at the time, White was literally just a friend of a friend, and the band had yet to release their own album. Peebles joked, "They were all starving to death on Hollywood Boulevard," and like in his earlier films, he had them transpose his musical snippets into full-length songs. He hadn't even heard the band play before: "I [hadn't] heard their music. I went to show them the movie and told them what I wanted. 'I want the tempo here, I want the sax like this, and I want dissonance there.' That's all."

The finished soundtrack, like the movie, is a hodgepodge of styles: there's movie dialogue cut over parts of the score; "Hoppin' John" is a slick, James Brown-influenced funk cut; the frantic "Come On Feet" first appeared on Br'er Soul. To be sure, the Sweetback's soundtrack is nowhere near as polished or fully realized as the later albums it helped inspire, especially Curtis Mayfield's Superfly and Isaac Hayes's Shaft. In fact, Hayes came to work on that album – the biggest of his career – because MGM Studios needed help with the soundtrack and approached Sweetback's label, Stax, which had Hayes on its roster. As Peebles explained, "When a little, unknown film, by an unknown guy and an unknown group, [succeeded like] this, everybody took notice. MGM took notice."

Yet, whatever Sweetback's lacks in refinement, the soundtrack still lingers with you, especially "Sweetback's Theme." What's so striking about the song is how sweet it is – for a movie about a hustler turned revolutionary who kills corrupt cops and escapes into the desert with hounds on his trail, his theme betrays none of that rage or darkness. In the movie we hear chanting over the melodic hook – "You bled my momma! You bled my daddy!" – and there's a tension between the visceral imagery of those words and the cheery swing of EW&F's playing. But there's something pure about the song's simplicity and how the singing horn riff patiently unfolds. "Sweetback's Theme," like the soundtrack and movie, has no standard to measure itself against, no precedent to converse with. It revels in that freedom like Sweetback revels in his. The theme plays out, again and again, a reminder that its namesake is still out there, still on the lam, still free.