The jury seemed hung when Tortoise released its fourth album, Standards, in the winter of 2001. Three years earlier, the band had wowed listeners with TNT, an overdub assemblage of nuanced jazz by an ensemble of instrumental aces. But it was unclear where the group would go next. Guitarist David Pajo soon exited, leaving the wonderfully eccentric Jeff Parker to handle guitar duties by himself. And in 1999, Tortoise served as the backing band for the first US tour of Brazilian radical Tom Zé—“the best music teacher you could imagine,” drummer John Herndon remembered more than a decade later. Those shifts and experiences granted the members of Tortoise the necessary license to push further than before. The result was Standards, which used “jazz” or “post-rock” as launching points to explore soul, funk, dub, electronica, and all points in between—and all in just 44 boundless minutes. The quintet’s devilish defiance becomes clear from the jump, as the opening track, “Seneca,” explodes into a noisy rumble that suggests Hendrix at Woodstock. But then Herndon and John McEntire lock into a staggering rhythm, as if Afrobeat played by John Bonham had been cut and built into dance-floor heat. By the end of six minutes, that beat is only the foundation beneath a mesmerizing prism of guitar lines, keyboard whorls, and hard handclaps. Elsewhere on Standards, the anxious gloom of “Benway” opens into vibraphone beauty, and closes again into math-rock knots, as tight as the muscle around a trigger point. And “Six Pack” balances krautrock insistence and haze with Grant Green guitar—an intercontinental fantasy of what instrumental rock could be. Standards was syncretic in a way that most other bands dared not to dream. Given that tizzy of sound, it’s easy to understand the mixed response to Standards back in 2001; there’s simply so much going on here. Some listeners championed the album as the future of post-rock—a crucial contribution in the expansion of indie rock’s boundaries. Others lampooned it as busybody noodling, an unfocused mess from a clearly talented band. The former camp was correct, of course. The soulful, slinking verve of “Monica,” the doomed lounge sprawl of “Firefly,” the intricate rhythmic games of “Eros”: These are the ideas and sounds that would soon become de rigueur in the widening gyre of indie rock, from Health to Bon Iver, St. Vincent to Zombi. Standards had a difficult infancy, but it was an artistic breakthrough—not only for Tortoise, but for the waves of bands that would follow the band’s lead.