Earls Court on a Friday night in February. Among an eye-socking pyrotechnic orgy of lasers, fireworks, flame belchers and steroidal PC screensavers, a 24-year-old Swede in a John-Boy Walton flannel shirt and a backwards baseball cap is twiddling knobs, faders, CD decks and a MacBook Pro. As a nod to the London crowd, the streak of bumfluff and drainpipes that Forbes magazine lists as the world’s sixth highest-earning DJ drops a medley of what he calls ‘site-specific’ tunes — Underworld’s ‘Born Slippy’, Arctic Monkeys’ ‘Do I Wanna Know?’, some bits of Candi Staton’s ‘You Got the Love’ — but it’s his own stuff, the jump-and-fist-pump hits, that really take the roof off: the zithery synth of ‘Levels’, the country-tinged ‘Wake Me Up’ (the fastest-selling single of 2013) and the cheesy Euro-house refrains of ‘Hey Brother’. Avicii mouths the lyrics like a teenage fan, conducts the tunes like François Truffaut’s character in the climactic scene of Close Encounters. There are 18,000 people going hands-in-the-air, girlfriend-on-their-shoulders nuts. It is all over by 10.30pm.