It was so dark, my friend noted, you could have had sex or done a Hitler salute. No stage lights, no stair lights, no desk lights, no door lights, no usher lights, no exit signs. The few wisps of illumination that did steal in created colossal shadows, giants freeze-framed on the walls. In these snatches the wooden ribcage interior of the Barbican Hall looked demonic. A few photons lit up the Autechre boys, Rob Brown and Sean Booth, who flickered like blue flames rising from a hob. A few more nudged into view the ceiling that had become a vast charcoal grisaille. When, occasionally, someone left, the tiny glowing portal that appeared made it feel as though we were at the bottom of a cavernous well. The barrage of doofs, thwangs, skwrshy-sweeshes of Autechre’s super-processed electronics also suggested we’d been plunged somewhere vast and inhospitable.