You’re familiar with post-rock, right? Long, usually instrumental tracks that start off quiet and pretty, build slowly then BOOM – erupt into cathartic crescendo, before tailing off with a swooning little coda. That’s post-rock. Beautiful and yes, intense, but formulaic; “alternative” muzak safe enough to accompany football highlights, teen melodramas and Sir David Attenborough whispering feverishly over infra-red footage of rutting beasts. Let’s rewind back to 1994. Mojo hack (and subsequent alt-music historian) Simon Reynolds slips the promo from a new British band into his stereo and presses play. The sounds which ooze from his speakers are alien – an…