MUSIC / Chemical reactions: Dominic Muldowney transforms base actors into singing artists. He talks to Mark Pappenheim

Songs yes, song-cycles certainly, music theatre maybe - but opera? Never] As a true man of the theatre, Dominic Muldowney has shown he has too much respect for text ever to subject it to the 19th-century gestures and contorted diction of the trained operatic voice.

Sixteen years into his job as music director at the Royal National Theatre, Muldowney has had plenty of time to contemplate the role of music on the stage, particularly in the setting of songs. When Muldowney sets a text to music, it's because he wants it to be heard - which means he writes only for registers that conform to the natural speaking voice (so no sopranos or tenors) and tries to set things straight. If a song has something to say, he believes, it should be spelt out in notes of one syllable: 'It's no good putting three notes on the word 'You', for instance,' he explains, 'if it's going to be heard as 'you', 'your' or even 'yawn' . . . I never set text melismatically - unless there's a reason that comes out of the theatre.' For, as he stresses, when it comes to writing theatre songs, context is all.

Above all, though, Muldowney likes his performers to sing a text as they would speak it. 'My cliche is that actually I think singing is an acting problem . . .' Mastering the notes is only the start. 'All my actresses have to learn the right notes and the right rhythms. But then they have to own it - and to own a song they have to find out who's singing it and why they're singing it and they have to do the whole acting process on it.' In the limited time usually devoted to rehearsing new music, the average concert singer, far from owning a song, rarely tries to do more than take up temporary residence in it. That's why Muldowney has withdrawn his songs from performance except by hand-picked artists such as Robyn Archer and Maria Friedman.

He's learnt from long experience that it's a much harder journey for a trained singer to come his way - 'and drop the posh' - than it is for him to push an actress into high chromatic trills. 'But I think they're both interesting and they both must happen - because until they do, I feel the century hasn't produced its new operatic mode. This thing called 'music theatre' just isn't good enough . . .'

Square Rounds, his latest theatrical collaboration with the poet Tony Harrison, is intended to be a further step on the road and not just another piece of 'music theatre'. 'When people ask me what music theatre is,' Muldowney explains, 'I always say there's only one piece of music theatre and it's called The Soldier's Tale and it happened nearly 90 years ago . . .' Muldowney and Harrison prefer to call Square Rounds 'a serious variety show'. The serious side is provided by Fritz Harber, the man who discovered how to extract nitrates from the air, and thereby paved the way for the development of both fertilisers and explosives. 'He also invented chlorine gas in the First World War,' Muldowney adds. 'The most bizarre thing about him was that he was Jewish, and the chemical weapons that he, as a scientist, discovered, went on to kill fellow Jews only 20 years later. So the whole piece has this incredible ambiguity.'

Magic provides the theatrical metaphor for that ambiguity: the set is one huge conjuror's hat and Muldowney's synthesised score draws on 'the sort of electronic music you get at magic shows'. Magic is also what he is hoping to work on the distinction between the singing and the acting voice. For, while all the company are women, all are also actresses - bar one, soprano Angela Tunstall. 'I call her my opera singer,' he says. 'She's the one who can read music.'

Most of the songs in the show are about gases - 'There's a Trinitrotoluene Song and a CO2 Song and an NO2 Song, a Laughing Gas Song, and a Song of the Nitrates'. Muldowney has written the one about Zyklon-B to be sung like opera - 'but it's high opera,' he adds, 'opera where you can't hear the words. So the song about the most horrible gas is sung in the most beautiful way'.

But the opera singer is not just there to set off the actresses like a special effect. 'In Square Rounds we're going from opera back to something rougher,' Muldowney says. 'I'm trying to find something that hasn't just got ingredients of both, but has actually transformed itself into a new object. We haven't quite achieved the alchemy - we still have this beautiful and this rough rubbing against one another, but just occasionally the chemical transformation occurs.'

In the meantime, when Muldowney really wants to write something theatrical, he writes a concerto. 'It's this whole idea of the relationship of the one to the group, that's what I call the theatre of it. It's the protagonist who comes out of the chorus.'

Muldowney has written four concertoes in the past 10 years: for piano (1983), saxophone (1984), percussion (1991) and violin (1992). His latest, for oboe, is premiered by the LSO under Michael Tilson Thomas on Wednesday (while John Wallace should be presenting a new trumpet concerto next year with Mark Wigglesworth and the Premiere Ensemble).

While, in the theatre, Muldowney happily makes his music the servant of the text, in the concert hall he gives free rein to his compositional concerns, above all to his increasingly complex experiments in polyrhythms. These reached their apogee in the Violin Concerto, where soloist Tasmin Little was continually forced to choose between two tempi, delivered by two orchestras, under two different conductors, each with a separate clicktrack.

The new Oboe Concerto, though, marks a break with such complexity. 'I did actually want a rest from all those clicktracks.' It is also, for a composer who now sees himself writing 'only songs and concertos', the best of both worlds - a set of songs without words for instrumental soloist. 'I listenened to Roy (Carter, the LSO's principal oboe) to find out what he does best - and what he does best is turn a phrase.'

Muldowney has given his oboist plenty of curvaceous lines, with a slightly modal, Japanese feel (partly derived from some theme music he wrote for the TV series, The Ginger Tree). It is, he says, basically a 'jolly piece', although it has a certain 'threnodic quality' inspired by the recent death of a colleague. 'So this plangent oboe is the perfect instrument.'

Oboe Concerto: world premiere, Wednesday 7.30, Barbican Centre EC2 (071-638 8891)

'Square Rounds', now previewing, opens Thursday, Royal National Theatre, London SE1 (071-928 2252)

(Photograph omitted)