"It's no joke when you're chasing the bus, growing older in a college town" sings Polvo guitarist/vocalist Ash Bowie on "Light, Raking," a moody, melody-bending standout on the math rock institution's sixth full-length, Siberia. This lyric is one of the only clues that could date Polvo's strange, stilted evolution. Siberia follows 2009's In Prism, the album that marked the break of a 12-year absence for the band but sounded more or less in line with the colorful math rock tones of their classic '90s albums. The 12 years in between saw the members of Polvo growing from college-aged kids making noise in their hometown of Chapel Hill, North Carolina to seasoned indie rock vets, still stationed in Chapel Hill and still focused on the making of noise. This focus shows on their albums that came after the reunion, and Siberia doesn't radically update the constantly shifting melodic math rock sound that made albums like 1996's Exploded Drawing so essential. The time away from the band seems to have resulted in a return to form, more so here than on their initial efforts with In Prism. Spirited and melancholic rockers like the epic "The Water Wheel" capture the same energy as Polvo exuded in their younger days, with the addition of unexpected tonal shifts from a bevy of overdubbed guitars and spaced-out tape effects coming in at the end to pull the rug completely out from under this epic tune. Album opener "Total Immersion" also sounds out of time, with its spindly riffs stretching out in many directions over the song's almost seven minutes. "Old Maps," while equally involved in its arrangement, leans toward the mellower side of things, its slow and mysterious interweaving acoustic guitar figures capturing the same distance and longing of Thurston Moore's 2007 solo album Trees Outside the Academy. Always challenging and ear-twisting without relying simply on atonality, Siberia is a step up from Polvo's original return to the scene. Though the songs here would have fit in with the best of their earlier phases, they manage to inject deeper subtleties and emotional crosscurrents than even their best work from the '90s without getting too soft in the process.