'COMPOSING like mad' is the present condition of Donnacha Dennehy, composer and founding director of the Crash Ensemble. He's spending a year in Amsterdam where he is not yet halfway through a sabbatical from his teaching post at Trinity College Dublin. He's three minutes' walk from the Concertgebouw and ten minutes from the Paradiso. He sometimes drops in on Louis Andriessen's composition class.

Nor is the city's thriving musical life the only distraction from composition for Dennehy. The New Year's hectic schedule of performances of his music requires him to check versions and respond to requests for changes of instrumentation and to various other contacts from performers. It all takes time.

It's also a pretty good barometer of his profile and success, a point which he never seems to think to mention. The London Sinfonietta is giving the première of A Game for Gentlemen Played by Thugs in February; the American group Ensemble Relache is performing Junk Box Fraud in Philadelphia and Baltimore; the Shobana Jeyasingh Dance Company is touring England with [h]Interland in February and March; and, back in Ireland, the Ensemble Integrales will perform Glamour Sleeper II in Belfast, Dublin and Bray in March.

No wonder he's busy. Just not as busy as he would be in Dublin. He is clearly delighted with all the time he can devote to composition. 'I'm loving being here,' he says with feeling, 'and I adore Amsterdam. It's a great city for music. And all during the day I just write music.' On his desk at the moment is a commission for Bang on a Can.

He professes to being much more relaxed whenever he is away from the claustrophobic smallness of Dublin and from the stresses of teaching and Crash. Down the phone from Amsterdam he sounds like his usual self, just more so: eager. Many subjects -- not all of them musical -- prompt from him an intense and enthusiastic concentration. It is pure zest, very often coupled with laughter. In equal measure he is both self-deprecating on the one hand and ready to mock on the other, good-humouredly slagging whole countries before revealing an actual affection for them. You can hear the glint in his eye as he disparages his own capitulation to the need for filing his scores and CDs in alphabetical order, or as he fillets certain aspects of America, France or Milton Babbitt.

The zest is child-like and must have been obvious to all around him when he was in fact a child. There was little in the way of music-making in the house, although his paternal grandmother played traditional fiddle. His mother liked Elvis Presley, and he remembers his transistor radio playing nothing but Elvis all day long on the day Presley died. He acquired the radio -- his first piece of music technology -- on his seventh birthday. His favourites were a catholic mixture of The Boomtown Rats and Music for Middlebrows. He was lucky to have a good music teacher in primary school who taught them all recorder. It was then that he began composing.

'I think at my first music lesson I started composition at the same time,' he recalls. 'I know I wrote very long pieces and I used to play them into a tape-recorder and then write them out.'

Meanwhile the recorder would eventually take Dennehy to the Royal Irish Academy of Music for lessons in both recorder and flute with Doris Keogh. He even played in her Capriol Consort (but did not, he emphasises, wear tights). 'I remember being very shy originally. Although maybe people don't remember me as being shy. Because I used to inflict my compositions on all of them. Doris Keogh would actually organise concerts where we played them.'

He reckons that his love of classical music began when he was nine or ten and his favourite composers were Bach and Stravinsky. 'I heard them both on this record, this rocked-up version, 'Concertos for the 70s'. Really dreadful. I shouldn't admit this at all. With kind of funky versions of the classics. This was before Hooked on Classics. A one-off. Much better, in fact, than Hooked on Classics. And there I heard the Brandenburg Concertos. And I went in and got the real Brandenburg Concertos after listening to this record, and I fell in love with them. Then, of course, I heard The Rite of Spring.'

This early love was nurtured by a theory teacher at the then College of Music, William York. York, whom Dennehy suspected was driven to distraction by classes full of 'mature' ladies wanting music appreciation, recognised the hunger for knowledge in his young charge. Their one-to-one lessons sometimes stretched to two-and-a-half hours.

'He really inspired me with a passion for twentieth-century music. For me, at ten, he was a very exciting character to go to lessons with. You always got the impression that his life was rather wild. But actually, he was quite a strict teacher. I was only ten or eleven, and he made me do all the Lovelock harmony exercises. Fugues, everything. I remember thinking that it was a pain having to learn all these rules.' I suggest that it says something about him that he was able.

'Well I worked hard on them. I was industrious and I had an appetite for it.'

It was York who encouraged Dennehy to go and experience Stockhausen during his visit to Trinity. He says it wasn't really love at first hearing. 'But I was more interested in Stockhausen then than I have been at any other point in my life,' he says with that glinty laugh. 'There's an element in Stockhausen that appeals to children. I did find it fascinating, but I found it much more difficult than Stravinsky. I preferred Varèse. I got into Varèse and I liked minimalism. Glass and people like that.'

I point out how far his theory lessons had strayed from the conventional College syllabus as I remembered it. 'We used to have discussions, for instance about John Cage. Actually I came across notebooks from the lessons. And in a piece I had written, one note had gone though to the other page. And his joke was, 'This kind of spatialised composition needs more control'.

'After York left Ireland, I didn't have that same sort of correspondence with anyone for quite a long time. I got these quite boring theory classes, and the Leaving Cert. didn't interest me at all: pat answers and no investigation. In my teens I lost interest in classical music altogether and became interested in pop and rock, David Bowie in particular.'

But his interest was re-awakened when he began in Trinity. 'Michael Taylor's analysis classes used to fire me up, both in disagreement and in excitement about the way he was looking at the music. I think we started it off with one of the Webern Bagatelles. The way he deconstructed this piece was like rediscovering the wheel almost. I found that very exciting.

'I used to adore Joe Groocock's counterpoint classes. It was like learning from an unbroken tradition almost. Of course, he had no feeling for new music at all. He was very conservative, but a nice man. And then [Professor Hormoz] Farhat was very encouraging. It was mainly because of his encouragement that I went to the States.'

Dennehy omits to mention that earning a Fulbright Scholarship also helped. This enabled him to pursue graduate studies in composition at the University of Illinois. But for a young man whose family had never travelled abroad, and whose only venture outside Ireland until then had been a visit to the south of France, life in America came as a major shock.

'It just struck me as like entering a TV set,' he recalls. 'Jesus, I thought. It really is true the way they show it on TV. I couldn't believe it. I would wake up in the morning and there was a motorway and a Dairy Queen and a Taco Bell. And I thought, I'll never be able to take this. Why didn't I go somewhere in Europe?

'It took me six months to get over that. And then it was great. There were twelve full-time composers teaching on the faculty. It's a music department that has orchestras and opera and is almost better kitted out than Dublin's entire musical life! It was a real eye-opener for me.

'There were great things like the Monday night Composers' Forum where you'd have concerts. Afterwards, everyone -- well, anyone who was brave enough -- would go to Herbert Brün's house for his seminar in experimental music which would last past midnight. And that would get very feisty. It was an extremely concentrated environment for new music.

'I was there at a lucky time, because Herbert Brün is since dead, as is Sal Martirano. They were two of my main teachers there, both of them firebrands in the 1960s. They had a real sense of engagement with the music, and also of questioning.'

Dennehy also spent a few months at IRCAM where he was surprised that the aesthetic was far less closed than he had expected. It gave him an opportunity to pursue his interest in spectral music and to encounter a more European perspective on music and technology.

'It's an interesting place where you have the mixture of the scientific approach and the musical approach. Sometimes I fear that an institution like that may spend too much time trying to justify its scientific research, and not enough in encouraging the kind of almost rhapsodic, accidental stuff of which art is really born. But I was surprised by some of the personalities there who were very open. I expected it to be very French with ten forms to fill in. But it wasn't.'

That was 1998. In the previous year, and not long after his return from the US, Dennehy was the driving force behind the founding of the Crash Ensemble. 'It was the only thing I could do. I really felt I wanted to set up something for the music I was interested in. Particularly music for mixed media, stuff that was quite rhythmic, and with a little bit of an urban edge to it. We weren't afraid to acknowledge the influence of rock because it's a very important part of our growing up now, anyone from my generation.'

In its first five years Crash was quick to assume a leading role within Ireland's new music scene. It addressed and brought in a whole new audience for contemporary music, attracted the interest and support of the Arts Council, and has been active internationally since 1999, notably with visits to Sweden, Germany and North America. In 2002 Crash created the separate position of director, appointing Fergus Sheil in time for the ensemble's high-profile Up North! festival of Irish and Nordic contemporary music. Dennehy, who continues as artistic director, believes the change is a step towards 'professionalising' the group.

'As much as I loved the early days -- we never started concerts on time, etcetera, which was all part of the excitement that had an almost rock energy to it, particularly for the classical establishment in Dublin which is probably the stuffiest I've ever encountered. As much as I loved all that, it really is time now to consolidate and have a proper structure. I want to make sure that the ensemble maintains itself when the initial euphoria about it is gone.'

I ask him about how he works. He had to leave his Broadwood piano in Dublin, so he uses a Clavinova as well as computer equipment including a sampler and a laptop. And lots of paper. He says that this -- what he calls 'the strict paper way of working' -- is the legacy of his classical background. 'I use very old-fashioned ways along with all these almost pop music ways of working. And actually I think the mixture works well for me. I sometimes think that some of the guys we have in the department of music technology in Trinity are too influenced by the technology. And then I think, Oh God if only they had all those years of the severe way of doing it that I had!'

But he understands the allure of the technology. 'There was a time for a while when I became really seduced by it and I would rely on it a lot. I've moved away from that now and I'm quite strict about when I'll play something back and when I won't.'

The empirical investigation of collections of timbres and of tuning systems is a central component of the process and one that only a computer makes possible. It can exist independent of the material and can happen before or after he has worked with the material.

'Sometimes I orchestrate first and then write the material. Sometimes it's all backwards. For me. I come up with a sound world, and then the material comes as well. Even though I have very distinct ideas about how I treat material, and I like sharp divisions and things to be quite clear, still I have that weird way of working.

'For this Bang on a Can piece, I dreamt the opening. That sounds very dramatic, but I did dream it. Because I was panicking. I always have about a month of panic before I start a piece. So maybe that's where it comes from: panic. Sleepless, restless, I suppose. And I did get a dream of the kind of sound that I wanted in this piece.

'So I went to my computer and typed down in words the kind of sound world that was in the dream. An essay. I then worked on it in different ways, in terms of sounds.

'There is a whole collection of different approaches. One is concerned with the sound, for which I use the sampler or the computer. And then another is the working out of something, for which I always use the piano. And then the paper for a more analytical way of working it out. I usually pin everything up on the wall. So I have pieces of paper -- all the sketches, the harmonies -- pinned on the wall. Indeed, I ruined the last place we were in. We had to re-paint the walls.'

Most of the time the ideas don't come to him in dreams. They just come. He was afraid they wouldn't come any more after he quit smoking two years ago. But they're still coming. And when he works with those ideas, the likely audience whether the 'stuffiest' -- classical establishment or the mix of niche-interest and youth that comprises a large portion of Crash's dedicated following -- makes no difference to him. 'I don't think about that. I just write the music that I want to write and that I feel excited about writing. I think that if you're too worried about constituencies then you should enter politics. That way of thinking can infect you sometimes. Because when you run an ensemble, there is a certain amount of your life that has to be engaged in the political as well. You have to apply for grants etcetera. But that should never ever interfere with your creative life. And that's why I am happy about having a proper director for the group.

'You write the music whatever way you write it anyway. I have great trouble with the idea then that it takes a connoisseur to understand it. Milton Babbitt's famous essay 'Who Cares if You Listen?' was kind of a war of words with John Cage. He was saying that you really needed people who were just like a neuroscientist. If someone in neuroscience was to present something, you'd want an audience of neuroscientists to respond to it. The idea of the audience being quite specialised. And that's anathema to me. Because the arts are different from the sciences in that regard.

'That's why sometimes in programme notes I avoid discussion of intervals or interval constructions and the tools of how you put something together. It happens an awful lot in music where people write programme notes that are full of jargon that you almost need a music degree to decode. There are different levels of experiencing that music. The people who are interested in these things have genuine inquisitiveness about them, and what they have to say matters as much to me as someone who's an expert.

'Compare Babbitt to Xenakis. Xenakis also used a lot of mathematical procedures when he constructed things. However, his pieces can have meaning for a listener who is unaware of all that. I did an analysis of the cello piece Nomus alpha which is done using group theory -- I think, if I remember right; it's a while ago! Anyway, he doesn't follow half of it in the piece as it's worked out. So obviously his ear kept on interfering: this way works, this way doesn't.

'What makes Xenakis really interesting is the sound and how these things help him control the sound. He used techniques to control sound. After all, that's all that we're interested in in the end: sound. Although Babbitt has one or two not bad pieces, you did get the sense that he expects you to perceive the structure in the same way that he constructed it. For example, that there is to be an excitement when the aggregate structure is not completed. Can you feel the pulse of that excitement?'