After putting post-rock on the map with their second album, Millions Now Living Will Never Die, Tortoise pushed into new territory on 1998's TNT. The forward-looking Chicago band tapped into the Windy City's long-standing avant-jazz scene to expand their sound even further. By the '90s, the jazz community first fostered by artists like Art Ensemble of Chicago included a whole new generation, and the presence of new Tortoise member Jeff Parker on guitar and guest cornetist Rob Mazurek marks the band's assimilation of that aesthetic. Of course, plenty of the old Tortoise elements are still in play here, like the Steve Reich–esque tuned percussion tapestries on "Ten-Day Interval," the pulsing, Krautrock-inspired grooves of "Swung from the Gutters," and the Afrobeat inflections of "The Equator." But from Parker's aqueous six-string tones to the increasing jazziness of the drumming, there's an undeniable opening-out process at work on TNT, as Tortoise prove that you can only be a truly progressive band if you keep progressing.