Since forming in 2006, Milwaukee’s Group Of The Altos has pegged itself as “a surly high school orchestra.” It’s a fine description, but it only gets half of the story right. At 12 members strong, the group certainly shares the size and breadth of an orchestra, with marching-band brass swapped out for violins, violas, and saw. But on the breathtaking Altos—a title to match a recently pared-down band name—the group’s demeanor isn’t so much surly as it is menacing. Recorded at Bon Iver frontman Justin Vernon’s April Base Studios, the album shares some of Vernon’s DNA (band member Daniel Spack also does time with Volcano Choir and Collections Of Colonies Of Bees), but it cuts a strange and troubling post-rock path all its own. Always inventive and never comfortable, Altos is the sound of a band creeping up behind you, and of a scene moments before the explosion.