I would try and sing but it sounded atrocious 
The actor formerly known as Leaf Phoenix has long moved out of the shadow of his talented, tragic older brother River. Reverting to his birth name he has carved out an impressive screen career in his own right, with highlights including Gladiator, The Yards, Buffalo Soldiers and Signs. Now he stars in James Mangold's Walk The Line, portraying music legend Johnny Cash in a performance that has already created a buzz of Oscar speculation.
So you play Johnny Cash - can you give us a song then?
I don't think you'd want that! And anyway I can't do it any more. It was amazing working on it and doing scales every day, strengthening the vocal muscles but I can't even do John's speaking voice any more. I don't have the same strength that I did. If you've ever worked out and reached the point of failure, where you can't lift a certain weight, it's like that. Your body simply won't do it, and it's the strangest feeling. But if you work at it you find that suddenly you can hit these notes that had eluded you for so long.
Given how familiar Johnny Cash is, it must have been important that you deliver a performance rather than an impersonation...
In every film, whether it's a fictional character or not, you create an idea of the character and for me I always do a bad impersonation to start with. For me the key was to try to understand why he did certain things that he did, as opposed to just impersonating him by saying you would move like him. For instance when he sang, I'd notice from watching, he'd always lift his head up. I kind of thought it was this interesting tic but after I watched it for a while I noticed that he was taking a breath, so he'd draw a breath and go back in and sing. So that's how I started learning to breath when I sang. So it became just a natural part of how I performed as opposed to thinking "I'm going to do this movement now". Those are the things that you tackled so that it doesn't feel like an impersonation.
Were you much of a singer before this?
It was all brand new to me, I've always loved music but never had an understanding of it, and never had the patience or determination to really learn anything. I always wanted to, and I liked the idea and I listened to music a lot. I would try and sing along with bands that I like but it sounded so atrocious that I couldn't.
Did you find it daunting playing a man so loved and admired?
Absolutely, but I feel that every time. Every time I do a movie you read a script, and for me when I decide to take a movie I have this overwhelming need to do the film, I have to do this. And then I go, "How do I do this? Am I going to do this right?" It matters a great deal to me, it's not just a job in that sense.
Did you regret not being able to talk with Cash directly?
In a way yes, but I was fortunate that he'd written two autobiographies. I had the unedited transcripts from one, and James Mangold worked really closely with him for a long time in the development of the story. So I didn't feel like I didn't have enough information, that I was relying on my imagination ever. But I would have liked to have spent some time with John.
But you had met him briefly before, hadn't you?
I did. James Gray, who directed The Yards, was shooting footage of John and June in the studio when they were working with [music producer] Rick Rubin. I'm not sure how my name came up but I think John was talking about Gladiator and Jim Gray said he knew me, John said he'd love to meet and invited me to dinner. As I was leaving he stopped me and said he liked Gladiator. He said what his favourite part was, and then he quoted this dialogue, the most sadistic dialogue you've ever heard. And he relished it. That was John.
Walk The Line is released in UK cinemas on Friday 3rd February 2006.
