Inevitably, it is very loud. You can hear the soupy rumble as Slayer start their set from the other side of the M8. Inside the SECC, the mosh pit thrashes, occasionally throwing a flailing body towards the stage. Thousands of young men in rude T-shirts nod in grim unison.
Welcome to the Unholy Alliance tour, a neat way for veteran blasphemers Slayer to win a younger demographic, and for young megastars Slipknot to stress that their roots run through serious death metal, not girly nu-metal.
Slayer have been going since the early 1980s, mixing grinding rock symphonies with assaults of thrash metal. It's not terribly subtle - there's only so many galloping guitar riffs you can listen to before you start to fancy a quiet paddock and a drink of water - but it seems popular with both the crowd and Slipknot, who do pretty much the same thing, only slightly faster and with masks on.
Visually, Slipknot's show is great. Each member has a slightly different mask (the effect can, in the right light, be rather unsettling), two percussionists are required to hit stuff with baseball bats, and lead singer Corey Taylor, who roars and shrieks but rarely really sings, marshals the audience until they are part of the spectacle, getting everyone to crouch down then leap up for Jump da Fuck Up.
Indeed, for a band who claim to hate humanity, Slipknot are big on communal gestures, taking time to inform the audience how much better this date is than the Belgian awards show they were forced to play the night before.
Still, Slipknot's wholehearted approach to entertainment could kick most indie bands into touch. The likes of The Heretic Anthem and Duality, meanwhile, have good tunes that leap from their brutal backing. For a band so infatuated with the dark side, Slipknot feel a lot like good, clean fun.
· At Birmingham National Indoor Arena tonight. Box office: 0870 730 0196. Then touring.
