CLASSICAL MUSIC / Master of the rolls: Bayan Northcott on Conlon Nancarrow, the maverick who crossed Bach with boogie-woogie on the player piano

Imagine spending decades at a mechanical contraption punching long rolls of paper with thousands of tiny holes. Imagine the mathematical exactitude required to plot out elaborate textures on the rolls even before the hole-punching can begin. And imagine, after months, even years, of anxiety as to whether the original piece was worth all the effort, finally feeding the complete roll into the works of a pianola and hearing for the first time a realisation lasting perhaps no more than two or three minutes. Yet, since 1948, such has been almost the sole obsession of Conlon Nancarrow.

His earliest years hardly suggest an emerging solipsist. Born in Arkansas in 1912, he studied music with some of the best East Coast teachers - Walter Piston, Roger Sessions, Nicolas Slonimsky - while supporting himself as a jazz trumpeter. And by the end of the 1930s he had begun to attract attention among American musicians of the so-called 'Experimental' tendency: that indigenous tradition of bold rhythmic constructivism which had been pioneered by Charles Ives and Ruth Crawford Seeger and was to influence - if in very different ways - the unfolding of Elliott Carter and John Cage. A Prelude and Blues for piano, published in Henry Cowell's questing quarterly New Music in 1938, already pre-echoed Nancarrow's characteristic concerns in a kind of Cubist, jazz-inflected Bach, deconstructed and reassembled with a relentless inventiveness.

Unfortunately, he had also begun to attract the unwelcome attention of the US administration. Inspired by the left-wing fellow feeling that linked so many avant-garde Americans before the war, he had taken himself off to Spain in 1937 to serve in the Abraham Lincoln Brigade against the fascists - almost losing his life in the process. On his return home in 1939, the government confiscated his passport for suspected Communist leanings and the following year he took permanent refuge in Mexico City - becoming a Mexican citizen in 1956. In the first few years of his exile, he continued to compose pieces for conventional ensembles, including the brief, moody-ebullient Piece No 1 for Small Orchestra (1943) and the frenetically folkloristic String Quartet No 1 (1945). But he had already been disappointed by the failure of live players to bring off his increasingly complex cross-rhythms. It was after briefly experimenting with a pneumatically operated percussion ensemble programmed by a piano roll that he found his answer in the pianola itself - or, as it was known in America, the player piano.

In a way, it was an odd answer for so manifestly progressive a composer. By the late 1940s, even the most sophisticated pianolas such as the pair of Ampico models Nancarrow managed to obtain - instruments capable of reproducing not just the notes, but the nuances of a great pianist like Rachmaninov - had been more or less outmoded by the gramophone. A few years later, and he might have investigated the emergent technology of electronic composition, as he himself has testified. But for the moment he was evidently mesmerised by the possibilities it seemed the pianola alone could offer: of measuring out streams of notes more precisely and rapidly than any pair of human hands could ever play; of superimposing multiple textures and tempi; above all, of structuring entire pieces according to the complex rhythmic relationships that had always been his primary interest.

Of the 60-odd Studies for player piano that have slowly accumulated since 1948, many of the earliest are constructed upon relatively simple, even banal materials - jazz inflections and vamping patterns, Spanish guitar harmonies, popular dance rhythms - but continually made to change gear, ambush and tumble over one another: an approach that reaches a climax of manic exhilaration in the extended Study No 7 completed some time in the 1950s. But in later Studies, two other concerns have become increasingly prominent. The first is an extension of the early penchant for hard- edged neo-Baroque counterpoint, in a series of canons of increasing complexity. In Study No 19, for instance, each of the three simultaneous lines keeps to its own tempo in the ratio of 12 to 15 to 21; while the whirling top line of Study No 21 steadily slows down against its retrograde, which equally steadily speeds up, the two crossing one another halfway like an X.

The second growing interest has been in the aural illusions created by swarms or tirades of notes too dense or rapid any longer to be distinguished individually - something he was only later to discover that such European contemporaries as Xenakis and Ligeti were also pursuing in the 1950s and 1960s. In Nancarrow's case, this reached its awesome apogee in Study No 41 a and b. Not only are these two pieces organised according to staggeringly complex internal rhythmic ratios, they are also conceived to be performed by Nancarrow's two Ampicos in precisely related simultaneity as Study No 41 c. The resulting torrents and vortexes of sound have to be heard to be believed.

Not that anyone much heard Nancarrow's studies in the earlier years, apart from a few old friends like Elliott Carter, to whom he sent periodic tapes. Carter at least responded admiringly by quoting a fragment of the Study No 1 in his own massive First String Quartet of 1951. Then in 1960 Cage arranged six of the earliest studies for a Merce Cunningham ballet with decor by Robert Rauschenberg, initiating a cult that was to lead by the late 1970s to the release in the US of recordings, made in Nancarrow's Mexico City studio, of the complete Studies up till then. And in 1985, the co-director of the Almeida Festival, Yvar Mikhashoff, succeeded in luring the reclusive composer himself to London for a few memorable days. Since rising performance standards were by now encouraging Nancarrow once more to undertake the occasional live commission, Mikhashoff proposed a collaboration in scoring up some of the pianola Studies too - a project only curtailed by his untimely death last year. Recently, however, the Ensemble Modern has issued a much-praised disc of the 11 completed arrangements (BMG Classics 09026 61180 2), and next weekend at the Barbican, the London Sinfonietta will be offering, as part of a jazz-inspired package, a chance to compare the arrangement of Study No 7 with its pianola original.

This will not be found a simple matter. There was always something paradoxical about the Nancarrow experience: of listening to a recording of a mechanical piano reproducing a composition which had never actually been performed in the first place. And while this might be likened to the effect of artificially generated electronic music, it is at the same time impossible to forget that the basic musical materials Nancarrow is drawing through this double reproductive process, indeed the very piano sound itself, are - or once were - the stuff of live music-making. A prolonged exposure to the pianola Studies can induce an irresolvable tension that seems not just aesthetic but almost physiological, and Mikhashoff's attempt to rehumanise the substance of the studies by giving them back to live players - and, hopefully, establishing them as bona fide works in the concert repertoire - is understandable.

But it may also prove beside the point - and not only because the scoring-up of Nancarrow's remorselessly objective pianola textures can sometimes seem to reduce them to surrealised Tom and Jerry cartoon music. For his real achievement is surely as a selfless discoverer, realiser and codifier of musical possibilities. Composers have always hankered after impossibly complex textures or superhuman virtuosity. From now on, anyone seeking to hear the exact effect of a boogie- woogie in five tempi at once, or a canon governed by proportions of two to the square root of two have only to pop on a CD of one of those coruscating Studies by modern music's master of the rolls.

London Sinfonietta 'Response' weekend, 21-22 May, Barbican, London EC2 (booking: 071-638 8891): includes Nancarrow's Piece No 2 for chamber orchestra Sat 7.30pm; an illustrated talk on the pianola by Rex Lawson, Sun 4pm; Nancarrow's Study No 7 (for pianola and arranged Mikhashoff), Sun 7.30pm