Singing in tune? That's so last century. The current trend in hip hop, soon to spread to the mainstream, is for the bravado off-key approach that puts character ahead of accuracy. Which means you've got to be flat to be cool

Last August the upper reaches of the British singles charts played host to a very odd record. 'Never Leave You (Uh Ooh Uh Ooh!)' was a radical rearrangement of 'Honestly' by Lumidee, a 19-year-old resident of New York's Spanish Harlem district. It was co-produced by one DJ Tedsmooth (aka Teddy Mendez), a man sufficiently aware of voguish musical currents to glue the song's vocal track to a Caribbean-influenced Diwali backing track.

The record was a dream-like delight, built on the most pared-down music imaginable. It was also fascinatingly out-of-tune: for the most part Lumidee sounded like one of those Pop Idol contestants fated to be ripped apart by Simon Cowell and Pete Waterman and hurled, sobbing, into the arms of Ant and Dec. Not since Crystal Waters crash-landed on Top of the Pops singing her inescapable 1991 hit 'Gypsy Woman' (remember -'Lah-dah-dee-dah-dah'?) had someone sat so precariously on the fence that separates the inexplicably addictive from the downright unlistenable.

'It's different,' argues DJ Tedsmooth, by phone from New York. 'Lumidee's not really a vocalist like a Mariah Carey kind of figure, so it's a vibe thing. And it sounds nice. Is it off-key? For sure - because we took the vocal from another record. Being a DJ, I do that all the time, but it always sounds sweet.'

Some came to different conclusions. 'Poor Lumidee can't even hit the notes!' marvelled one early review posted on the internet. 'I mean, if it's a personal style, OK, but this girl really wants to get it right and just dies. Couldn't she afford pitch correction?'

'She is out of tune,' says Radio 1 DJ and R&B authority Trevor Nelson. 'Blatantly. When they heard that record, a lot of my friends who are DJs immediately screamed and shouted and said it was the worst thing they'd heard all year. I didn't agree: I knew it was out of tune, but it just worked. Some records do that. Pete Tong jumped on that single very, very quickly. He wasn't as precious about it, not being a hip hop or R&B DJ. I played it to my producer and he said, "She can't sing, she's out of key." But I put it on at a club that weekend and it went down a storm.'

The Lumidee single is only one of dozens of records released over the past year that suggest a strange new development. Within both R&B and hip hop (which, let us not forget, exert a gargantuan influence on the pop mainstream), it is currently the thing to proudly flaunt one's vocal imperfections - and on occasion to embrace borderline tone deafness. A string of high-profile examples prove the point: such stars as Pharrell Williams (half of the much-worshipped production duo The Neptunes; see review, page 10), OutKast's Andre 3000 and the trainee R&B diva Ashanti are prone to come over like enthusiastic karaoke turns, implicitly acknowledging that vocal gymnastics are beyond their grasp, and sounding endearingly like human beings.

Those perceived as strait-laced rappers, meanwhile, have only furthered the sense that musical precision is currently an irrelevance. Ever since the New York artist Ja Rule spread the idea that atonal non-singing could sound like the acme of cool, droves of hip hop stars have followed his lead. Look at the million-selling 50 Cent: his street-tough poses are surely underlined by those moments - as on 'P.I.M.P' and '21 Questions' - when he attempts to grapple with a tune, manages two or three mumbled notes, and implicitly laughs in the face of musical convention. It was not always thus. In the days of rap music's old-school beginnings there was an implication that musical hooklines were best left to one's DJ; to sing would somehow be to compromise one's outlaw spirit. On the few occasions any rapper tried a melody, the attempt usually had clownish overtones - a point best illustrated by the fact that while Public Enemy's hip hop pioneer Chuck D stuck rigidly to an imperious, stout-chested rap delivery, his ghetto-camp sidekick Flavor Flav was occasionally allowed to break into song. As the likes of '911 Is A Joke' and 'I Don't Want To Be Called Yo Niga' proved, however, he was not exactly Luther Vandross.

In time, as rap music began to bestride the charts, the importance of an infectious chorus became hard to resist - but, perhaps on account of the experiments outlined above, rap stars were encouraged to leave this aspect of their music to the experts. 'If you were starting someone's hip hop career 10 years ago,' says Trevor Nelson, 'you would definitely have said, "Do not sing under any circumstances. We'll get an R&B singer to sing the hook." That was the norm. But now the rappers are keeping it all to themselves. They know they'll get away with it, and they don't necessarily want an R&B singer on the record. It's, "If it's my record, I'm singing on it". There's no shame in it any more.'

This, when you think about it, is no bad thing. Not long ago rap's air of hard-faced cool was rather compromised by an accent on airbrushed commerciality - witness the smoothed-out chorus on Coolio's 'Gangsta's Paradise', Faith Evans's contributions to Puff Daddy's unbearably icky 'I'll Be Missing You' or Mya Harrison's cooing vocals on Pras's 'Ghetto Superstar'. Now, by contrast, the importance of platinum records seems to have been belatedly squared with the eternally vexed problem of one's credibility. In short, you can have that oh-so-important chorus and Keep It Real.

In DJ Tedsmooth's estimation there's even an argument to be made that those with poor vocal skills are often forced to compensate by making more inventive music. 'If people have got great voices that's not so much about creativity - it's more raw talent,' he says. 'If you're more limited you've got to work on the content. It becomes more about what you're saying than how you say it. And if you ask me, you get a better record.'

The latest addition to the ever-expanding choir of Bad Singers is showcased on 'Slow Jamz', a huge American hit by the Chicago rapper Twista. An unabashed ode to carnality, it finds the producer Kanye West lumbering up to the microphone and delivering rib-tickling vocal lines in the sub-musical style du jour. 'She got a light-skinned friend, look like Michael Jackson,' he drawls. 'Got a dark-skinned friend, look like Michael Jackson.' Crooned by some big-lunged virtuoso, the humour might be all but lost; here, the medium melds perfectly with the message. In the words of the New York Times: 'Mr. West has figured out that many listeners want to be charmed, not floored. And whether he's singing or rapping, his sly, matter-of-fact delivery makes every track sound so slightly conspiratorial; we're all in on the joke.'

'Kanye West is one of the hottest talents in urban music,' says Nelson. 'And he's very smart. If he's off-key, he'll be doing it on purpose. I think some of these guys have a tendency to do it deliberately, even if they've got a good voice. It's as if they've just smoked a couple of cigars, had a load of Cristal, bit of bourbon - just woken up, haven't cleared their throat yet, and it's, "Let's hit the studio, man". It's perfect.'

One striking possibility is suggested by all this. If the idea that one should be able to warble like Mariah Carey is about to be expunged from the mainstream, should the music industry's impresarios now be looking for people who can't sing? Having just rejected the imperatives of body image, should the makers of Pop Idol now forget about the necessity of being in tune? Come to the think of it, might there even be an opening for that poor soul whose reading of Survivor's 'Eye Of The Tiger' so brightened our lives last year?

'I'm not sure about that,' says Nelson. 'You've got to remember: you can only go off-key if you've got credibility. Don't you dare try and come into the marketplace with no street cred, and go off-key. Manufactured off-key artists won't work. I think kids are a bit smarter than that. They'll take it from grimy hip hop acts, they'll take it from people who come of the streets, but they won't take it from Simon Cowell. No way. I'm not having that at all.'