Rock star side projects have a notoriously chequered history. From misguided attempts at re-invention to full on vanity projects, whenever a renowned guitarist puts down the six stringer and picks up, well, almost anything else, the results are usually dreadful; mention classical music and you’re in full-on Nigel Tufnel territory, complete with sniggering about the influence of “Mach” and D Minor being the saddest of all keys.

But then the National’s Bryce Dessner is not your average rock star. For a start, classical guitar is his first love, picked up when he was just 14 years old, and a passion that led to him earning a Master of Music degree from Yale University in 1999. Add in his many collaborations with the likes of Steve Reich and Phillip Glass, his work with Kronos Quartet, his numerous production and curator credits, and the fact that he’s currently composer-in-residence at the Muziekebouw Eindhoven in Holland, and it’s easy to see that St. Carolyn by the Sea, his latest classical offering, is no mere side project.

“It’s part of what I’ve been doing for a long time,” he tells me down the phone from New York, and the ambition and detail on show over the 43 minutes of music he recorded with the Copenhagen Philharmonic leaves you in no doubt that this is the work of a master at the very top of his game. With influences ranging from Jack Kerouac to Blind Willie Johnson via a 16th Century English lutenist, Dessner – alongside his twin brother Aaron – weaves a sublime spell as the music ebbs and flows through a whole range of emotions. It’s contemporary yet reverential, ambitious yet enjoyable and, for anyone who thought he was just a guy who played guitar in another (admittedly brilliant) rock band, something of an education. Turns out his more famous day job is just the tip of the iceberg...

DiS: Can you describe the project?

Bryce Dessner: It's a new record that pairs three orchestral compositions of mine with a suite of orchestral pieces by Johnny Greenwood, brought together by a German conductor called André de Ridder who was kind of the engine behind the project. We worked with the Copenhagen Philharmonic, which is a great orchestra, to record the pieces. The three pieces of mine are ‘St. Carolyn by the Sea’, which is a double guitar concerto that I played with the orchestra and my brother Aaron, another track called ‘Raphael’ which uses electric guitars alongside strings, wind, brass, and percussion, and then a newer piece called ‘Lachrimae’ which is a big, orchestral piece inspired by the English composer John Dowland. Johnny's suite is made up of pieces he wrote for the score for There Will Be Blood.

What prompted you to release this now, in terms of timing?

A lot of this music was written over the course of a long time, but it's only now that it's being released. It was just the opportunity; the orchestral world has opened up a lot in recent years, and there are very creative ensembles now, like the Copenhagen Philharmonic - they do some pretty adventurous programming. Recording an orchestra is obviously a big endeavour, and expensive, and this is really the first time for a project this large that it came together in a realistic way. There's another album of mine coming out this year, of string quartet music that I did with Kronos Quartet, and so it was just the timing, and the way it happened; it takes a while to write the music, and when the opportunity came up with the orchestra it just felt right. Also, a lot of this music was written for the concert experience, and it's less about me thinking about it being an album – each of these pieces has it's own story, was commissioned for a different group, and was developed on it's own timeline, but they all came together in a concrete way and I just thought it was something that would make a good album. So it's a combination of all those things.

How different is the process of composing a classical piece of music, compared to writing a song as part of a rock group?

I always say that I'm the same musician, regardless of what I'm doing; whether it's rehearsing with the band or I'm at home working on a piece for a more classical setting. The difference is that with the National, we're very collaborative, so we bring simple songs or sketches of songs to the band and then the process of writing, developing, and recording them is the work of five people. With the classical stuff I'm doing, there's a couple of things that are different; the way I generate music and think about it, whether that be improvising with the guitar or using the piano or whatever, is similar, but the process of making the work is quite different – I do 90% of the work myself, where I'm working to notate scores, so I really have to think through all the details on my own. There is a bit of collaboration that goes into the performance side and recording – with André, we were both very involved in shaping the music, and even in some cases editing it. And with certain ensembles, like Kronos Quartet, there is collaboration that happens as well. I would say that the inspiration for music and the way that ideas come is quite similar, whether it becomes a classical piece or a rock song, but then the actual process of making it is different; the National writes in the studio, and we really use recording as part of our process, but with my classical music I really focus on notating the music and making sure the score is really clear, so the musicians can read and understand it.

Do you find that classical composition gives you a greater sense of liberation and freedom when it comes to writing? It seems far less constrained that the traditional structure of rock music, or a rock song.

Formally, I'm able to do more ambitious things in my classical music, and it's a really healthy counterpoint to rock songs, which tend to have an economy about them, and a stripped down immediacy. That's really important, and classical musicians can learn a lot from rock songs and from rock musicians. I've really learned so much from spending so many years writing rock songs that when I'm composing longer pieces, I still try to keep that kind of energy in them. But ultimately, you're not constrained by radio format, or thinking about what it would mean for a vocalist to follow, so I'm able to explore more adventurous sonorities – ‘Raphael’ is almost 20 minutes long – and can develop some of the ideas further in such long form works.

At certain points, especially on ‘Raphael’, it's almost like there’s a cross over between classical and rock, similar to what Sigur Rós do. Is that a fair interpretation?

I know the guys from that band – some of them have a similar background to me – and in a way, some of their rock music feels orchestral. But they write songs, whereas ‘Raphael’ is, by nature, a drone piece, based around a harmonium, which was the central instrument in it. So if you're hearing that, it’s probably there. It’s not necessarily intentional on my part, but I think Sigur Rós have done amazing things with sound and texture, and even using orchestras on their records, so there could be a similarity there.

I didn't mean so much a similarity in the music, but in that it straddles both worlds in a way; like it has one foot in the rock world, and one foot in the classical world, trying to use elements of both.

Yeah, I think you’re right. There’s certain rhythms in the percussion for instance in ‘Raphael’ that maybe have more in common with rock driven drumming, and some stuff I did with the strings and orchestra and what not...again, the way I go at these things is I don't necessarily think that way, or think I'm mixing in different things from different styles consciously. For me, it’s just all part of my language, and I feel free. There's also bits of folk in ‘Raphael’, little quotes from this great blues slide guitarist Blind Willie Johnson at the end from a song of his, and I'm able to reference freely; whatever or wherever the piece brings me, I don't worry too much about what the genesis of the idea was, it’s just part of my language.

You included the six-piece suite from Johnny Greenwood, from There Will Be Blood. Was his success with those pieces of music an inspiration for you to do this album, and to release something concrete in terms of your classical composition?

No, not really. I think that we're like minded musicians in many ways – Johnny is a classical violist – and we're both very close to Steve Reich, an American composer, and we've both worked with him. But my interest from music stems from being 14 years old, and playing classical guitar and studying at Yale, so it’s part of what I've been doing for a long time. Johnny wrote that music for an amazing film, and it works incredibly well as a suite for orchestra, so the choice to include it was made by the conductor André de Ridder – he was really the third collaborator on this record. Ultimately, writing for orchestra is, for me, more about enjoying the format, and I feel like I have something to say. It's such a creative and diverse sound for a musician, it's a fantastic instrument to write for, but Johnny and I approach it in quite different ways actually.

Do you have ambitions to score a film?

Yeah, I think if the right opportunity came up I would definitely do that. I wrote some music for a ballet recently, for the New York City ballet, which I loved doing. The guy's name is Justin Peck, he's a choreographer at the NYC ballet, and it was a piece for a LA based company called LA Dance Project; a twenty minute piece where I wrote the music. It’s different from scoring a film, but in a way it’s nice to write music that has a purpose outside a concert hall. At some point, probably with my brother, we'll try scoring a film – it would be interesting to do something new.

So nobody has ever approached you?

No. We've had lots of queries about doing it, but finding the right project is a little bit tricky.

What would you consider to be the "right project"? What criteria would you use to say yes or no?

Well, I think the way that Johnny [Greenwood] worked with Paul Thomas Anderson on movies like There Will Be Blood and The Master is great. He's a really collaborative director who believes in a musician and is interested in the music playing a big role in the film; that would be exciting. And then it’s partly subject matter – we'd have to think about what kind of film it would be – but with the National, we've done music for movies like Win Win, we did some stuff for The Warrior, and Matt has done a song for Game of Thrones. It's always really fun to have your music used in that way, so it’s definitely something we'd be excited to do.

You played St. Carolyn by the Sea last May at the Barbican. Do you have any more plans to perform it this year, and what is your actual role while on stage?

I'm doing it in Cincinatti and Germany in March, and again in Mexico in the fall. Both my brother and I play guitar with the orchestra, so I'm on stage performing – the pieces were composed that way. But this May, at the Barbican, I'll be premiering a new piece I've written with Kronos Quartet – so we'll be a quintet – for electric guitar.

The title is from a book by Jack Kerouac. What is it about his writing that inspired you, and why did you choose it?

When I was writing St. Carolyn by the Sea, I was reading his book 'Big Sur' – it’s kind of a memoir novel, written when he was basically losing his mind from alcoholism, and he died a couple of years later – but the book itself has this incredibly dynamic arc, and it's written as he’s living in this little cabin on the Californian coast, near Big Sur, and the imagery and the hallucinatory arc of the book itself feels orchestral. It also mentions Stravinsky a couple times, and that vista, of the great Californian ocean, has a grand orchestral feel about it. I often take non-musical inspiration from things like that for my instrumental pieces. It's also actually an image from the book; he's sitting on the coast, and his lover in the novel, this distraught woman, is wading out into the ocean and he thinks she’s going to drown herself like Ophelia – that’s where the Carolyn comes from. I just thought it was this beautiful image, and dramatic, and so that piece – the title track – is inspired by the book and, in a way, goes through a series of intense mood shifts and follows the drunken hallucinations of the book itself.

You mentioned Stravinsky, and Steve Reich earlier; what other classical composers or performers are you inspired by in particular?

I've been really lucky in my life to have worked with a lot of the great minimalist composers who are now in their mid to late 70's – I've toured with Phillip Glass, performed and recorded with Steve, and performed with Terry Riley. And then the generation after them, people like David Lang, has also been a big trigger for me. But more than that, I grew up playing classical guitar, and playing things like Bach and John Dowland [English lutenist and composer] – ‘Lachrimae’ is actually inspired by a specific Dowland work. Bartók is probably my favourite composer for strings, so that's definitely an influence, and there's also an experimental Polish composer called [Witold] Lutosławski whom I like, so I have pretty diverse interests in the classical world.

Given that perhaps not a lot of people are aware of your background in terms of classical training, and studying at Yale, are you worried that this album won't be taken seriously? That people might just think "Oh, another rock star side project" and not realise that it's a big part of your life, and a big passion for you?

Not really, no. It's not the first record like this that I've released, and I think that rock fans and critics are quite hungry for new music and are pretty open-minded. Ultimately it's music that people should relate to as music, and they're free to have their own opinion on it; I don't necessarily have any kind of brilliant plan about that. I just hope people will find it enjoyable and that it'll transport them somewhere, and that others will take the time to seek it out. I mean, it’s not easy music – it does take some time to listen to and get into – but I think if people spend time with it they'll hopefully enjoy it.

How was it working alongside your brother Aaron on the project?

My brother's really amazing. He doesn’t have the same background in classical music that I have, but we've been making music together since we were kids. I followed a more academic path and he's more self-taught, but we’ve been playing together since forever, so he's really, really great – I barely have to teach him anything. We have a very symbiotic relationship and he's very supportive of all this music. In a way, he’s always right there when I'm doing these more experimental projects and I think it has it's own kind of influence on what he's doing as well.

You mentioned how it was inspired by Kerouac's 'Big Sur', and how you were struck by a lot of the imagery contained in the book. Would you say that thematically, this album is a classical version of an Americana album, with the same kind of themes and imagery that the likes of Bruce Springsteen and Woody Guthrie use?

In terms of the subject matter, the record is definitely...there's this idea of the West, and the ocean, and there's an emotional energy in it that might feel distinctly American on some level. For me, I definitely do weave folk music influences into all this stuff; there's a bit of slide guitar in there, and ‘Raphael’ was in part inspired by a Blind Willie Johnson blues song called ‘Dark Was The Night’. So there's some of that stuff in there, it’s just maybe looked at though a different lens than you would find in a folk song.

What are your future plans in terms of classical composition? Do you have any new music written or collaborations lined up?

I'm writing a large orchestra piece actually, for the Los Angeles Philharmonic for next May, so that's kind of a big thing. And this May I'm at the Barbican presenting a new piece with the Kronos Quartet for electric guitar – May 13th I think – and I'll be performing with them. I'm also going to write some music for my friends, some solo pieces for really great instrumentalists that I work with, and I'm really enjoying writing this music – so far, I've had lots of exciting opportunities. It’s always a balancing act seeing what I can do with that music while still having time for the band and touring – eventually I guess we'll start thinking about music for a new record – so it’s just a case of making sure I have time to do it all! But I'm enjoying having both things in my life for sure.

Bryce Dessner: St. Carolyn By The Sea / Jonny Greenwood: Suite From "There Will Be Blood" is released on March 3rd via Decca.