Urban Classic, Hackney Empire, London <!-- none onestar twostar threestar fourstar fivestar -->

Four rappers in unison make a mighty sound, but the biggest noise at the Empire was the squeal of institutions jumping into a fashionable bed. The BBC's Concert Orchestra and two of its radio channels, the Arts Council and the PRS Foundation, even the Black Police Association - they were all backing Urban Classic.

That label "Urban" was there again, and when the orchestra's conductor Charles Hazlewood showed up wearing a hood, so was a hint of condescension. Top-of-the-bill singer Terri Walker didn't show up at all, so we had to skip the climax of the evening ("a fusion of urban and classical music") arranged by composer Jason Yarde and grime producer DaVinChe.

But it was a good night for a succession of MCs, Purple, Bruza, Pase and Tor, who rode the waves of sound, thrived on them, and finally hauled some excitement out of a slow-burning audience. Tor, with her brand of spiky and unmacho rap, had a particularly warm reception. The night's star turned out to be Faith SFX, the beatboxer who can mimic anything from drum loops to violins, sometimes all at the same time, as in his virtuoso song "Pony". He hardly needed an orchestra since he could do it mostly himself, and his deconstruction of the Godfather theme came close to sending up the whole show, but he was also the one who seemed to get the biggest creative boost from the orchestra's presence.

The event was the climax of a year's work, much of it done behind the scenes by the youth development agency Bigga Fish. If the workshops found any edgy new sounds, they were left well behind in the end product which featured several proficient examples of safe, professional-sounding orchestration. Some tricky patterns went into it, but at these levels of amplification anything dense disappeared: you could see timpani pounding away but rarely hear them, and in the final number's massive tuttis only the percussion and one melody line registered. Double-bass and big drum needed boosting with electric guitar before they even suggested sub-bass. Nothing attempted the rhythmic subtlety of Pase or Tor. Simplest and boldest worked best: strings only, a four-note clarinet riff, strong figures cutting through.