SILVERCHAIR frontman Daniel Johns gives a dry laugh. "Some days I can walk, other days I can't. Some days I walk with a cane. I've still got this arthritis thing but other than that I'm all right." Not exactly the state of health he was hoping for on the eve of the release of his band's first album in three years and with a year of international touring ahead.

This "arthritis thing" is the result of a virus that has left him with swelling of the knees since Christmas, requiring cortisone injections and restricting his usually boisterous stage presence on the band's tour with the Big Day Out festival in January.

The pain worsened after a trip to London to visit his girlfriend, singer and songwriter Natalie Imbruglia.

"All the doctors can tell me is to wait and be patient," he shrugs. "At the moment we're sitting around waiting for my knees to deflate."

But Johns also has a little secret that is helping to ease the pain, one which will be revealed when the new album, Diorama, hits the stores from tomorrow and – like their three albums before it – inevitably debuts at No. 1 on the Australian albums chart.

The secret? Diorama might just be the best rock album you will hear all year, and such a bold reinvention of the band's sound that it is sure to alienate some of their millions of fans around the world while winning over others.

Comparing Diorama with the band's teenage years as bleak, post-grunge rockers is like comparing Sgt Pepper with the first Beatles album.

Where once the Silverchair sound was dense, distorted, angry; the new approach is cinematic, epic. Orchestral arrangements are an integral part of the sound. At 22, Johns's songwriting and vocal performance have matured to the level suggested by the sneak preview single, The Greatest View.

Silverchair can still hit like a sledgehammer when the song and occasion demands, but anyone expecting a reprise of hardcore anthems like Freak or Abuse Me is in for a rude shock. And, obviously, hasn't been paying attention.

Johns, the band's singer, guitarist, songwriter and driving force, explored the use of orchestral arrangements on 1999's Neon Ballroom album, which featured classical pianist David Helfgott on one track and showed the broadening scope of his pen on tracks such as the powerful Ana's Song (Open Fire) and the gentle piano ballad Miss You Love.

Johns admits he was "over traditional rock" by the time he was 18, and more lately has dabbled in experimental recordings with Sydney musician Paul Mac and released them on the Internet in late 2000.

The name of the project? I Can't Believe It's Not Rock. It's clear that Johns knew even then where his music was taking him and what Silverchair fans might say when they heard it.

Not to mention the reaction of drummer Ben Gillies and bassist Chris Joannou. Despite their youth, they go back a long way – Gillies started making music with Johns at primary school in Newcastle, where they were soon joined by Joannou to play a repertoire of Led Zeppelin, Deep Purple and Black Sabbath songs learnt from their dads' record collections.

"The time I was most nervous about this was showing them the songs and wondering what they were going to think," Johns says. "A lot of this record was written at a time when I didn't even know if I was going to do another Silverchair record.

"I wasn't that I thought the music would be too complex for the band, but I thought the public's perception of the music would be so out of whack with what they were used to from Silverchair that the record might be ignored."

After their initial shock, Joannou and Gillies gave an enthusiastic response to the material and Johns decided to proceed with Silverchair.

The dark emotions that drove the world's biggest teenage hard-rock band are gone, replaced by the perspective of someone who had struggled with the demons of teenage stardom and felt good about coming out the other side.

"The last album especially was very black with shades of grey," he says. "This time I was trying to project a sense of colour, a broad spectrum so that people would feel uplifted after listening to it.

"When you're at that age you have that feeling of alienation or whatever it is you're feeling angry about. Now I've grown up a bit and look at things differently.

"My music had always been a projection of what I'm feeling at the time, whereas with this album it was a conscious decision to make the music influence the way I was feeling. Even if I was feeling down, I'd try to write something uplifting to try to change my perception."

At the time Neon Ballroom was released, Johns admitted to having suffered – and recovered from – an eating disorder which inspired Ana's Song.

His teenage years were anything but normal, his band discovered by a Triple J/SBS competition and their Frogstomp album storming into the American top 10 in the year they had turned 16. It went on to sell more than 2.5 million copies worldwide.

Would he recommend that level of fame at such a young age for his own children?

"Definitely not, but that's not to say I don't think it can be a very positive thing to have early success. I feel incredibly proud of what we've done.

"But if I had my own kids I wouldn't be pushing them into it at an early age. I don't think it's good for self-esteem because you start judging yourself on how other people see you rather than how you are.

"If you become popular at 14, people start judging you in the media. That's a time when there's a lot of self-doubt in your mind; you don't know who you are or what you're doing, you're still trying to discover yourself. When you start reading people's negative perceptions of you at such an early age it's not going to do you much good."

Johns says the unusual circumstances in which they found themselves – high school rock stars – helped them cope.

"We were still at school in Newcastle. You get back from a two-month tour of America at 15 and all of a sudden everyone's calling you 'faggot' or 'gay singer boy' or whatever. You couldn't get carried away because there were too many people who hated you!"

These days, Johns can see the funny side of a bad review. Perhaps he's bracing himself for some strident reactions as headbangers try to get their heads around Diorama.

"Obviously when we're recording a song like Across The Night after three albums that don't sound anything like that, you wonder if people are going to like it or think you're a pretentious idiot, but that never changes the direction I'm taking. I'm quite selfish in that way. When I'm writing music the only person I'm trying to impress is myself. All I want to do is make myself sit back at the end and go, 'I didn't think I could do that'. "

Many others will be thinking the same thing when they hear the orchestral sweep of Across The Night, a majestic pop tune that opens the album with a direct challenge to the Silverchair audience.

"People had told me that song shouldn't be the first track because you should ease people into the direction that the album has gone. But it always felt like an opening track from the moment I wrote it. It's inviting you down this new path, and some people are going to choose not to go down there and some will embrace it."

While the album was recorded in Sydney with American producer David Bottrill, Across The Night is one of three tracks featuring the exotic string arrangements of legendary American songwriter/producer/arranger Van Dyke Parks, who worked with Brian Wilson on the famous "lost" Beach Boys album Smile and was the co-writer of its best-known survivor, Heroes and Villains.

His 1968 debut album, Song Cycle, with its lavish arrangements, is still hailed as an art-rock masterpiece. Despite their 40-year age gap, Johns knew instinctively Parks was his man.

"Someone suggested him to me. I hadn't heard him, but when I listened to the Beach Boys stuff he had worked on and some of his other work he blew me away. I thought we were on a similar wavelength."

They were. But the songs he worked on – Night, Tuna In The Brine and Love Your Life – are far removed from the old Silverchair. "Dude," you can hear the conversations going in malls across the land, "I can't believe it's not rock."

The symphonic element doesn't stop there: It carries on throughout, even in the hard-rock riffing that concludes Without You, one of the few places on the album that has anything in common with the wave of nu-metal bands that have rushed into the vacuum in Silverchair's absence.

Classical music has not been an influence, Johns says, but neither has much else. He kept every form of music at a distance in the creation of Diorama so that he wouldn't be influenced by others.

The Van Dyke Parks songs provide a core to the album, but these are just one part of the mosaic, from the lumbering metal riffs and prog-rock grandeur of The Lever to After All These Years, a tune with a piano flourish that Freddie Mercury would have been glad to call his own.

Best of all is a song called World Upon Your Shoulders, a healing, emotional epic that marries Beach Boys-standard harmonies to a rock tune as sophisticated as U2 on All That You Can't Leave Behind and Led Zeppelin at their zenith. And electric guitar music doesn't come much more powerful than that.

Johns knew he was on to something special even as he was making a demo of the song at home with a drum machine and cheap bass sound.

He remembers the night clearly when he was recording the song's guitar part in the studio. It was September 11.

"I had this big dilemma in my head about whether I should go to a D minor or a D major chord. I went to get a cup of coffee and saw what was happening on TV, and then I knew what chord I wanted to use meant nothing.

"The record was made at a time when the world seemed quite disturbed and a lot of that comes across. The uplifting qualities are there because they are trying to overcome a time in the world that felt anxious and fragile."

At a time when the ephemeral and the slickly targeted steal valuable air time from music that really matters, Silverchair, like U2, aspire to something higher.

When you hear something as compelling, as complete, as moving, as World Upon Your Shoulders, you know Silverchair had no choice but to shed their skin and begin again.

Diorama is available in stores from tomorrow on the Eleven label through EMI.