"Thirteen" is the thirteenth studio album by the cult British progressive rock band Soft Machine. This album, composed of previously unreleased tracks of exceptional quality, marks a new chapter in the band's sixty-year history. While the lineup of Soft Machine has undergone many changes since its golden age in the late 1960s, the group's spirit of musical adventure and its ease in evading labels have remained constant, navigating effortlessly between powerful progressive jazz-rock, atmospheric psychedelia, free improvised jazz, and loop-based ambient music. "Thirteen" features legendary guitarist John Etheridge, a member of the band for over fifty years who is once again at the peak of his art. Although all four band members contribute to the composition, the album's primary composer is saxophonist, flutist, and keyboardist Theo Travis, who wrote six of the thirteen tracks. The most recent member to join the band is drummer and composer Asaf Sirkis. The album is incredibly rich and far-reaching. Among the tracks are "Open Road," a rock piece where the band lets loose with fiery solos from Etheridge and Travis; the ballad "Disappear," which begins with ethereal flute loops and transforms into a beautiful piano miniature, without drums. "Turmoil," composed by bassist Fred Thelonious Baker, is full of unleashed fuzz bass, frantic solos, and an almost uncontrollable racket. "Daevid's Special Cuppa" features an appearance by founding member Daevid Allen (his guitar part having been recorded years earlier, with the track built around it). On "Thirteen," Soft Machine has never sounded bolder.