Despite his acclaimed interpretations of music by Radiohead, The Beatles and Nick Drake, Brad Mehldau is still unapologetically a jazz musician, he tells Shane Hegarty.

BRAD Mehldau is lounging in a Chicago hotel room, killing time until the evening's show. He's touring America in the middle of the election and confirming something he already knew: you don't get many Republicans in jazz.

"It's weird because I'm a partisan Democrat. I'm as partisan as they come. And everybody I know is too. And if you do a tour where a lot if it is in the periphery cities and the coasts, you're meeting more Democrats. You wouldn't know that there were Republicans. Then you turn on your TV and you see them."

Mehldau's jazz is a liberal's jazz. He's a classically trained pianist best known for improvised interpretations of songs by Nick Drake, The Beatles and Radiohead, but he's gotten a bit bored of promotional hype that says he "defies musical borders and makes you not care about jazz, or whatever. For me, there's always something great about saying unapologetically, I'm a jazz musician. Because when jazz is good there's nothing like it. It's so free and you can get into this ecstatic place that you don't get in other types of music.

"Of course, that's a generalisation. You can get it in other types of music, but jazz can go to a sort of place that's really unique to it."

It's easy for Mehldau to say that, of course: at only 34 he already has an astounding recording back catalogue and a reputation as a fine live performer. Albums with bassist Larry Grenadier and drummer Jorge Rossy have earned him the tag as the next great trio leader after Oscar Peterson and Keith Jarrett.

His solo performances, meanwhile, have become increasingly confident, as confirmed by Live in Tokyo, the new album in which he improvises songs by Porter, Gershwin, Radiohead, Monk and Drake. Each is both complex and beautifully simple, his performance energetic yet controlled. Mehldau once remarked that "music kind of yokes together the feeling of attainment and the feeling of loss at the same time", and there could be few more precise descriptions of the music on this record.

"I've been trying to do more solo sort of stuff steadily over the years as I feel that I have something to say. That's what it comes down to. So I've really over the last year or so been steadily practising solo piano concepts and trying to get something that's my own. And it's required a fair amount of physical practising to get to a point where I can execute, technically, things I'm hearing in my head.

"It's much more physical than playing with my Trio because I'm using more of the instrument and more of my left hand and I'm doing more difficult things, just from a technical standpoint."

Listen to Live in Tokyo and it's hard to believe there is only a single piano played by only two hands. But that show, recorded last year, was a near perfect night for Mehldau, on which he captured the songs in versions he was happy with, on a piano he loved, having done what he does on his day off: play the piano. But his current tour mostly consists of Trio shows as he tries to master the solo gigs, tries to get into the "psychic space where I really have no fear."

"Solo, there's a little more of a gap between a good performance and a performance that I'm not happy with. Where with the Trio it's levelled off a little bit. It's either good or really good or, very occasionally, it feels like it's not so good. But with the solo I can sometimes feel that I'm really struggling, because I'm trying to develop my own language or vocabulary approaching a solo performance.

"And there's a fair amount of trial and error there. I'm practising a lot. Sometimes the trial and error comes out in the performance. On the other hand, when I think I had a bad gig, a lot of times I realised the audience didn't realise all the stuff I was tripping out in my head."

Without wishing to sound facetious, given that much of what he performs is spontaneous, is it likely the audience even notices?

"That's a good point. I think one of the greatest skills in improvising, and it's not really talked about that much, is this ability, when you do something that you didn't intend to, to instantly, in that split second, make it sound like it was completely intended. And then to do something interesting and fun with what you didn't intend to do. In fact, you can start spinning a whole way of playing out of what's there, a certain amount of stream of consciousness.

"With the solo stuff, there's more of an opportunity to engage in a stream of consciousness. I'm not tied to meshing with bass and drums, so if I really want to go off on a tangent I can do it."

Mehldau's ability to find repeated depth in pop and rock songs has moved him outside of the straightforward jazz audience. Those who might find the eclecticism and audible whoops of Keith Jarrett a little off-putting can happily lose themselves in Mehldau's 19-minute take on Radiohead's Paranoid Android, enjoy the way he can disappear down a musical alleyway yet always return to the centre. And how he never plays the same song the same way twice.

"With classical music, I'm the kind of person who goes into one thing very deeply and stays there for a while," he says. "I did that with a lot of heavy-on-the-Germanic classical stuff. I got into Brahms 13, 14 years ago and got so into it and stayed there and stuff around it, such as Schubert and Schumann. And it's a slow process because there's so much music there.

"And I think it's a different world but it's the same kind of exploration, the same pace that's taken place for me with a few bands or singer-songwriters like Nick Drake and Radiohead and The Beatles. I guess what they all have in common is a certain melodic sensibility - just the fact that there is a melodic sensibility - and the beauty to the harmony that oftentimes overlaps with classical romantic harmony.

"Certainly with Nick Drake, River Man [ which closes Live in Tokyo] has been a staple for a while, and there have been certain songs over the years that have stayed with me. For whatever reason, some always remain compelling to play for me and that's always the test, whether I emotionally respond to playing it."

Mehldau fears that he'll get a little bored of music, find it harder to find the inspiration and excitement. He wonders, is this what being a professional musician does to you? He remembers when, as a 15-year-old in Hartford, Connecticut, an old drummer he used to play with would tire of talking about new records, saying that when a chef eats a good meal he doesn't call up all his chef friends to tell them about it.

"I kind of think what he was getting at was that once you are doing something, once you're putting it out there, you don't necessarily have that fetishic interest with everything that's involved with what you're doing. So I suppose it's about finding a balance and not letting that collapse into a cynicism. I have a sort of obsessive drive to absorb things still because there's so much music out there. And I don't want to, for my own ego and satisfaction, feel like I've pigeonholed my own musical identity."

At the moment, his CD player is helping him "finally get into the 20th century, now that we're into the 21st". He's listening to the French composer Olivier Messiaen and discovering Aaron Copland's piano sonatas. Also, Björk's new record is "blowing me away".

Having leaned so much on other people's songs of late, Mehldau is writing original material again. He recently performed with and wrote for a New York quartet, which included Grenadier, and is adapting that to the Trio, although he has no immediate plans to record. Elsewhere, Carnegie Hall has commissioned him to write for soprano Renee Fleming.

He's shy on who he would most like to collaborate with, only saying that he would love to work again with Jon Brion, who produced 2000's Largo, the album of which Mehldau is most proud.

Of his grander ambitions, he simply talks of "being able to grow old in music and to have a life in music" and to take the pain if the steep upward curve starts to plateau or slide. "So for me I guess that's my only goal. It's a sort of non-goal in a way, because it means, in terms of practical reality, staying open to the possibility of change."

For the moment, a world tour goes on until March, and he takes a moment to sweet-talk the Irish a bit. The audiences here, he says, have always been good to him, knowledgeable and appreciative. He'll play a Trio show in Cork and solo show in Dublin, coming here having played shows in Spain. "I love it in Ireland. I love that cold, and the ... maybe 'melancholy' is too strong a word."

Mehldau is being sincere. "I'm a north-easterner, so I feel tied to that in a certain way," he adds, having moved from Los Angeles to an hour north of New York City five years ago when he "married and settled down and did all that". And even more immediately, he has a little more time to kill before his show in Chicago.

"I wish I could say that I was interested in absorbing the culture of everywhere I go, but that's not really the case. Sometimes I just go to the hotel and sort of do nothing and then go straight to the gig. That happens a lot."

Live in Tokyo is available on Nonesuch. The Brad Mehldau Trio plays Cork Opera House on Sunday, November 14. Mehldau plays a solo concert at the National Concert Hall on Monday, November 15.