The name of the decade-old, Chicago-based record label comes from a 1959 teen flick that referred to a bunch of young miscreants as thrill jockeys. There isn't much in the way of delinquent behaviour on display tonight, however. The crowd may be here to rock, but they are here to rock thoughtfully - and, judging from the exhausted bodies littering every carpeted corridor and stairway, many of them have been doing so for the full, celebratory 10 hours.

Thrill Jockey made its name with post-rock, so tunes you can whistle were thin on the ground at Ocean - but the label's profile is broader than that. Brokeback, for instance, dip into jazz and ambient hip-hop, while alternative rock veterans Eleventh Dream Day deal in raw, buzzing guitar freakouts. The Sea and Cake are another kettle of cod entirely. With just two guitars, they manage the illusion of massed orchestration. They can whip up storms of plangent noise, but when frontman Sam Prekop sings against the odd breezy melody, you wonder if he has just rediscovered 1980s Brit-poppers Orange Juice.

If less is more, as the post-rock diktat probably has it, then nobody told Bobby Conn. Dressed in a white parachute suit, he is the wild card in the Thrill Jockey pack, possessed of a falsetto so extravagant he makes Prince sound like Darth Vader. Performing solo and triggering the sampled accompaniments himself, the oddball Conn trills and yowls his way through a lovingly crafted pastiche of 1970s American radio rock. Trans Am, next on the bill, are his kindred spirits: their pulverising guitar riffs and screaming synths veer towards heavy metal, but there is a sweetness beneath the sludge and it is all very carefully measured, despite the physical ferocity.

Headlining duties fall to reluctant post-rock gurus Tortoise, who have long since outgrown their reputation for sterile, tricksy, quasi-jazz instrumentals lasting three days. With two vibraphones, each about as big as an airport runway, the quintet work up plenty of rippled, skittish grooves alongside more solid blocks of muscle-bound rhythm. They fill the room with endless, subtly shifting planes of sound that are as light and lush as a pointillist painting.

"Geniuses!" shouts one overwhelmed punter. Maybe not. But after just five ineffably funky minutes, you realise Tortoise's name is their little joke.