Played without warning in any public place, Washington, D.C., band Orthrelm's OV a single 45-minute instrumental track will induce hysteria. Some of the terror comes from the music's sonic proximity to distress signals: Riffs blare like air-raid horns, and other guitar notes hover at an urgent pitch like Emergency Broadcast System tests. For properly prepared listeners, OV can be intriguing. It's a Frankenstein's monster of disembodied death-metal fragments, and its serrated slivers of melody and spiral percussive patterns seem to play a little differently each time. It's a musical marathon for players and listeners alike, the rare show that gives spectators a sense of accomplishment upon successful concert completion.