Jamie Foxx's startling portrayal of singer Ray Charles has been snapping up awards across the US. Donald Clarke talks to the hot actor about winning the great man's approval, as well as prejudice, impersonation - and teaming up with Colin Farrell for Miami Vice.

In the right context, the phrase "Who the hell is that guy?" can be the most complimentary thing you can say about an actor. While watching Michael Mann's problematic 2001 biopic, Ali, I found myself mouthing those words every time the actor playing the champ's eccentric corner-man, Bundini Brown, opened his mouth. Such quiet confidence. Such dignity. Who is that guy?

Jamie Foxx (for it was he) had, in fact, been around for a while. Born 36 years ago in Texas, Foxx, who was raised by his grandmother after his parents split up, displayed any number of talents as an adolescent. After flirting with professional football and recording a decent r&b album, he eventually decided to try life as a stand-up comedian.

Though he tasted success alongside Jim Carrey on the American TV show In Living Color, the rest of the world knew little of Foxx before Oliver Stone cast him as a mouthy quarterback in the gridiron drama Any Given Sunday. Last year he stole Mann's Collateral from Tom Cruise. And now, playing the late musician Ray Charles in Taylor Hackford's sure-footed biopic Ray, Foxx has become a favourite for the Best Actor Oscar.

"I don't quite know what's happening to me," he laughs. "Everything I have tried till now is just right out of the park. I'm using a baseball analogy here. I have just knocked it right out of the park. Now, when I was young, I felt that I could rely on my youth, but now I know it's about preparation. I learned that from Jim Carrey."

Though some have suggested that the performance has more to do with impersonation than proper acting, there is no question that Foxx's work on Ray is quite astonishing. He carries himself so like the singer that one immediately forgets their physical dissimilarities. At times, particularly during the extended musical sequences, he almost seems to be channelling Ray's spirit.

Interestingly, Foxx was reluctant to spend too much time with Charles, who, sadly, died a few months before the picture's release, in case geriatric mannerisms would creep into his performance.

"Quincy Jones gave me a tape of Ray on The Dinah Shore Show and it was a whole different voice: faster, higher. We had to work hard on modulating his voice as the movie went on." Nonetheless, shortly after he secured the role, Jamie did go and meet Ray to seek his endorsement. It proved to be a gruelling encounter.

"He was very, very happy that we would take an interest," Foxx says. "We got to play together on his piano, and every time I hit a wrong note it'd be: 'Why the hell would you do that? The notes are right beneath your fingers. Life is about those notes right underneath our fingers.'"

Just when Foxx was getting the hang of the music, Ray would drop in a tricky Thelonious Monk riff. "Oh yeah, and it was like I was retarded. Then he gave me that speech and said: 'Just play it'. That's what I mean. That was his test. 'Let's see if you can get past this, man.'"

Foxx, who plays the piano almost as well as he does everything else, secured the veteran's seal of approval. It is perhaps surprising that Charles was supportive of a project that deals so unforgivingly with his heroin addiction and many adulterous affairs. Though the film may be a celebration of Ray Charles's life, it is certainly not a hagiography.

"He wanted all that stuff in. But in Ray's mind I think he knew that he was on the way out and he wanted it all told. Maybe if there were no health complications then it would have been different, but you never really know. He wanted the truth told.

"We were fortunate that this wasn't a big studio film. We were able to tell the story of the drugs because it was an independent company. If it was a big company it might have been: 'We can't do that. We can't tell that story. We are trying to sell this and that.' Pepsi generation. America. All that shit."

The film paints a bleak picture of the Georgia in which Ray grew up. The singer was barred from performing in the state after refusing to play in segregated theatres, but received a formal apology in 1977 when the state legislature adopted his great ballad Georgia on My Mind as its official song.

Following the civil rights campaigns, the Texas of Foxx's youth must surely have been a little less starkly segregated than Georgia in the 1940s.

"Oh no. It was just the same. It still is the same," he says sadly. "There hasn't been enough time. Hip-hop changed things a bit. That embodied a lot of things. But really it's the same. There were these railroad tracks in my town that divided it and I had to go to school on the white side of town as we called it. And they would call you 'nigger' or run you out of their town. You got used to it, but you never really understood why it was that way."

He shakes his head in puzzlement. "I have never even been in my local newspaper and it is only 12 pages. I have never even been put on the front. It doesn't worry me, but I will never do an interview for them. They phoned a while back and said [ adopts shit-kicking, redneck voice] 'Would you come on down here and do the parade or something?' No man, because you used to run me over. Not everybody in the city was like that, but it was that way often."

These comments mark a rare sombre interlude from a buzzy, energetic performer who finds it hard to get through a sentence without dropping in a noisy impersonation. The young Eric Bishop - Foxx selected his unisex stage name to hoodwink bookers hungry for female stand-ups - must have been quite a handful for his hard-grafting granny, who died just a few months ago.

Clearly impressed by his talent, the old lady forced Jamie to take piano lessons from the age of three. He became his high school's quarterback while simultaneously honing his talents as a crooner. But, somehow, comedy won out.

"Comedy won out because it was the only thing you could do without anybody else having to validate you," Foxx says. "If you are playing football then somebody can say, you're not good enough. If you try to act you have to audition. With stand-up you are a gun-slinger. You walk into the saloon: bang bang! You can cook it instantly, right in front of you. Also, you can work on your acting, your jokes, your delivery. It's a training ground for everything."

In Ray, we see the hero working his way from dive-bars up to grand theatres. The show-business world of the 1950s seems to have been awash with vice. I don't imagine Foxx came across any drugs or fornication when he was starting out as a comic. Surely not?

"Haaaa! There were woman and drugs everywhere, man," he laughs. "But you know that doesn't go with my culture. My culture is healthy. When I was coming up I was an athlete; drinking was cool, but in moderation. And then you see what cocaine and heroin did to people and how it fucked them up, and you don't want to do that. You can't maintain life like that.

"But women will always be the most incredible creation and they make you do things a little better. If there are a lot of women in the audience then ... it's not that you want to be with all of them ... but it still makes you up your game a little bit."

Foxx has a young daughter, but is no longer with the child's mother. Maybe it's time to settle down. "I don't know, because it's kind of fun the way it is right now. It is fun being single and enjoying life."

Talk of the high life brings us on to the events of April 2003, when Foxx was arrested in New Orleans for assaulting a police officer. He pleaded guilty to a misdemeanour offence and received a six-month suspended sentence and a $1,500 fine. It seems the incident started when his sister was hassled outside a casino. Does he have anything to add to the story?

"Oh, man, no," he says, screwing his face into a clenched fist. "No there is nothing to add; it was what it was. Yeah, but sometimes - I know you'll have experienced this - you'll be having a great time and then somebody comes in and tries to wreck it,.I guess I have to learn to lay back a bit."

Foxx is certainly capable of formidable levels of discipline. Throughout the shooting of Ray he wore prosthetic eyelids, rendering himself as blind as the singer he was playing. To paraphrase Olivier's famous comments to Dustin Hoffman, what is wrong with just acting, dear boy?

"Taylor suggested we should go blind and I said yeah immediately. Otherwise we're cheating. When a door opens you will anticipate it. There are certain things you can't cheat properly. Actually, being in the wrong place in the room is different to just pretending you are. The uncertainty of Ray Charles was unique: being not quite at the mic and so on.

"I had to get used to that blindness real quick and I hyperventilated a lot. Every time I went to put them on, in fact. I'm being closed in for 18 hours and I got to eat lunch like this. If somebody visits the set I don't know who it is, so I am just waving. It was a jail sentence."

Of course, when he finally came to see the film, much of its look came as a surprise.

"In-fucking-credible! Oh, they had these dresses on. And look at the blues, the reds, the yellows. I cried quite a few times - complete sensory overload. The performances of everybody else. The women. The way Taylor put it all together. It was amazing."

Viewers who think of Ray Charles as something of a middle-of-the road performer will get a real sense of the dirty energy of his early music. Foxx, who appears on the recent, highly acclaimed LP by hip-hop star Kanye West, is eager that the film should play to younger audiences.

"I'm so happy that people like Kanye West, people like The Neptunes, people like Puffy got to see it. I said to them 'You are going to be amazed by this movie because it's you.' But also people who haven't been to the movie theatre for years are going. One of my friend's father said 'I ain't been to the movies since '72, but I am going to see this Ray thing. I want to make sure that this kid didn't fuck it up.'"

Next up Foxx will be joining Colin Farrell ("A great guy. He was a really stand-up guy during that whole Alexander thing") in Michael Mann's big-screen version of his own breakthrough TV series, Miami Vice. Will it be a pastiche? "No, not at all. If it turns out funny then it's a failure. We are looking at that great first season, not all that pastel stuff. Michael Mann has been all over the world researching. It's not just set in Miami."

So Jamie will be wearing socks? "Oh yeah," he chortles. "It will be the looks of today - Aston Martin, Armani. The movie is set in 2000 and infinity"

Ray opens next Friday