The following correction was printed in the Guardian's Corrections and clarifications column, Thursday 15 July 2010
The date of Stockhausen's death was out by a year in the article below. He died in December 2007, not 2008.
In the summer of 1963, Karlheinz Stockhausen came up with a project for a composition class he would teach that autumn. On holiday in Sicily with his lover Mary Bauermeister, he worked out a structure which would involve transformations of seven different kinds of music, explaining later that "as I couldn't take a lot of paper with me, I tried to hide in the shadow of a rock with Mary, and we drew them in the sand together".
The result was Plus Minus, a score which provides some basic musical material, and then much more elaborate instructions for turning that material into a finished piece – a sort of flat-pack composition. These instructions are encoded in seven pages of diagrams, with more pages of text explaining how to interpret them. In the shade of their rock, Bauermeister and Stockhausen refined their symbolic language so that it could show not only the characteristics of each musical event, but also how they might grow or contract: the plus and minus of the title.
Each frame of the score is a subtly varied re-combination of the same abstract forms: lines, circles, triangles, squares – much like early 20th-century constructivism (Bauermeister was a painter). It is also formidably complicated. Anyone wanting to make music from it has to be willing to spend hours deciphering the symbols, and then many more hours translating each constellation of symbols into something that musicians can actually read.
In 1998, I was invited by the Dutch new music group, the Ives Ensemble, to work on a large-scale realisation of Plus Minus. It took months, a process of trial and error in which I would translate a few symbols, discover I had misunderstood an instruction and have to start all over again. But by May 1999, we had 40 minutes of music ready for performance; now, 11 years later, we have a CD recording.
It was a strange experience. I was composing, yet not writing my own music, referring every decision back to Stockhausen's instructions, some of them quite ambiguous. So why did I do it? Because Plus Minus comes from the middle of a 20-year period in which Stockhausen invented some of the most extraordinary music of the last century. Working on the score was like having a composition lesson with him at the height of his powers.
Stockhausen's success owed much to his attention to detail. Photographs of the West German Radio studios in Cologne where he worked show a space like the control room of a power station, the composer flanked by banks of dials. Battling with technology that was never intended to produce abstract soundscapes, he would create dazzling effects which pass in a moment. Today, they could be achieved with a couple of clicks of a mouse; then, they took hours of careful configuration of oscillators, filters and tape machines.
As Stockhausen became more famous, this concern for detail tipped over into full-blown megalomania. Promoters would be presented with lists of demands, specifying everything from the colour of the microphone cables to the size of the composer's bed. He also started to make fixed versions of several open-form works.
Somehow Plus Minus evaded Stockhausen's revisionism. Perhaps because no one had made a satisfactory version of the piece, he felt there was nothing to fix. Whatever the reason, when I started work on it there was remarkably little on which to build. When the music was ready to perform, and then to record, we thought about contacting Stockhausen. But we worried that he might want to intervene, even attempt to stop us, and after years of work we decided to go ahead without him.
We reassured ourselves that the piece had been in the public domain since 1963 and that there had been other versions before ours. Stockhausen had said it was a piece which could "have its own children". If he was the father, did that make me (and the Ives Ensemble) the mother – and, if so, what were our parental rights?
Stockhausen died at the end of 2008 and can no longer tell us what he thinks, but I'm sure his many fans will. I suspect that those who like our recording will praise Stockhausen, and that those who find it wanting will blame me and the performers. It's not so much about ownership after all, more about being a parent.
• Plus Minus is out now on Harmonia Mundi
