Nils Frahm/A Winged Victory for the Sullen review – BBC 6 Music's late-night middle youth rave

They call it neo-classical, post-classical, indie-classical – but here’s what it comes down to: a German in a deep-V T-shirt hammering at a keyboard, while, up in the stalls, fanboys play air piano and weave hand shapes. At such points, none of the evening’s signifiers – late-night prom, presented by 6 Music – seem fair warning for what verges on a seated rave.

You might not have expected such antics from pianist Nils Frahm or ambient duo A Winged Victory for the Sullen. Frahm’s early recordings are brisk, elegant piano pieces, while AWVFTS (their unwieldy choice of acronym) sum up their modus operandi in the opening track of their first album, We Played Some Open Chords and Rejoiced. On paper, combining these labelmates looks less like a big night out and more like three-quarters of a rather stubbly team on University Challenge.

Yet, tonight, both acts supersize their shows. Opening, Dustin O’Halloran and Adam Wiltzie enlist the support of three string players, the five-piece London Brass ensemble and three dancers from Company Wayne McGregor, with whom they collaborated on the 2013 piece Atomos. The extra bodies fill the stage without somehow distracting from AWVFTS’s warm, amniotic sound.

Ramming home the idea that this is a middle youth rave, the two sets mix into each other, with Frahm playing into the last five minutes of A Winged Victory. The Berlin-based soloist sometimes makes his melodies too pretty and finished and, at first, as the audience cheers on big tune Says, the effect is rather like Richard Clayderman landing up in the chill-out room of a club circa 1993. But he wins you over by sheer virtuosity and attack.

Darting between a giant piano, an organ, a Fender and a sampler, Frahm sometimes broadcasts loops of the refrain he’s just played; sometimes attacks the strings of his piano with toilet brushes. All this is lapped up by the crowd, an affable bunch who look like they’ve just rolled out of a tent at Latitude with barely a pitstop for a shower and a sourdough toastie.