It is a cliche, but not without good cause: hip-hop struggles live. Producers-turned-performers is perhaps the only other subgenre to fail so regularly before an audience. Therefore the London debut of hip-hop's hippest producers, the Neptunes, under their N*E*R*D (No One Ever Really Dies) banner, should have been a farrago. In fact, they almost confounded every expectation.

N*E*R*D have already done that once this year. On what seemed to be a whim they re-recorded their digitally created debut album, In Search Of... , with Spymob, an all-white quartet signed to their label, StarTrak. The results were eyebrow-raisingly successful. At Shepherds Bush Empire, Pharrell Williams and Chad Hugo appear alongside three-quarters of Spymob and a passing keyboardist. The group are as flexible live as they are in the studio: they are lithe on the ghetto morality tale Provider, then prove just as capable of Body Count-style manly rocking on the exhilarating Rock Star, which wouldn't sound out of place in a Red Hot Chili Peppers set.

The Virginian duo certainly do not fail in the songs department. The encore Stay Together is soft and lovely, Run to the Sun is pop psychedelia and Lapdance as tough as teak. Despite its eclecticism, In Search Of... is virtually flab-free and little of its craft and invention is lost on stage.

Producers or not, Williams and Hugo's workrate is Stakhanovite. From the off, the tactile pair hurtle into the reverential but giddy crowd. Williams takes the bulk of the vocals and makes the speeches between songs ("We're on the other side of earth. Wow"), while Hugo does the perfectly timed shouting, swearing and genital thrusting. When the crowd sing along during Bobby James, the rueful saga of a drug hog, N*E*R*D are full of pathos.

So near, but so far. Halfway in, they introduce another StarTrak act, Kelis. After a sterling turn on Truth or Dare alongside Williams and Hugo, the pair leave Kelis to her own momentum-killing devices and lightweight material. "It's been a rocky year," she confides, introducing a speech that may still be continuing, "I changed labels in the US and I... "

And then, disastrously, there is Williams's voice. He is a dextrous rapper, but he simply cannot sing outside the carefully controlled studio environment. When he tries to croon Things Are Getting Better, it is as if Jimmy Durante were fronting Jamiroquai. Your heart could break for him.