At festivals of contemporary music in the early 1970s, a young Romanian composer was regularly in evidence. He had large features, which drew attention to him even when he was not saying anything — as was commonly the case. When this young man did speak, he would often denounce what had just been performed. More rarely he praised, but his comments always came with a humour just touching self-mockery. The ambition was evident: also the strength of mind and intelligence. It seemed clear to those near him he would make something of himself. Horatiu Radulescu did.

Radulescu became one of the most extraordinary composers of recent decades, though his works were appreciated more on the fringes than in the mainstream. Like others among music’s oddball visionaries, he found his natural home away from the musical establishment, whether in France, where he spent nearly all his adult life, or elsewhere.

The basic principle of his music was simple and ancient: it was to use tones that are related to one another in the manner of natural harmonics, with wide intervals below and increasingly narrow ones above. By compounding large numbers of such tones he sought to create sounds that have the complexity of those of nature, and also sounds never heard before: immense complexes stretching up to the furthest extremes of which musical instruments are capable. In order that enough tones were available, and that they could blend together, Radulescu often found himself writing for large arrays of similar instruments.

One striking example is his Byzantine Prayer, for 40 flautists placed among the audience, another his Fourth String Quartet, in which nine quartets, eight of which may be prerecorded, are heard from all around the auditorium.

Such works could not have been brought to performance without the belief that Radulescu inspired in performers, such as the flautist Pierre-Yves Artaud and the Arditti Quartet.

These works are, too, bound to have the aura of a special occasion, an aura which they live up to by the strangeness and potency of the sound they generate. Tuned to the frequencies of natural harmonics, the notes depart from normal scales and often involve very narrow intervals. Multiplied by many instruments, the effect may be of wails, hums, groans and ecstatic cries coming from a gigantic voice.

Radulescu himself spoke aptly of “sound plasma”, of sound as continuous and yet constantly changing as new combinations of the available instruments and notes are brought into play.

But this was only one facet of his work. He also pursued his fascination with unconventional tunings in solo pieces, notably Das Andere for a string player, which executes a mesmerising slow descent from the topmost heights, where the musician plays crystalline melodies, interrupting these with gruff broken chords. Another sequence of pieces involves what he called a “sound icon”: a grand piano turned on its side and either bowed or struck. Yet other works might be disarmingly normal, an example being his piano concerto The Quest.

Radulescu’s concern with the physical matter of sound — how it is constituted from harmonics, and how this knowledge may be used in composition — sometimes caused him to be labelled a spectralist, along with such French-born contemporaries as Gérard Grisey. However, he was in the field ahead of them, his earliest “spectral” piece being Credo for nine cellos, composed in 1969. He also kept his distance from these colleagues, as from most others.

His intellectual and spiritual company he found, rather, among great masters from the past — Leonardo da Vinci, Pythagoras, Daoist sages — and among the musicians of many cultures and eras who shared his sense of sound as divine. “The music we are composing is, above all,” he wrote, “the music of a special state of the soul, and no longer a music of action.” Time might seem to be stopped, for a single sound to be explored to its furthest reaches.

Radulescu studied at the Bucharest Conservatory during a time, the 1960s, when new ideas from Western Europe were being actively endorsed by the composers who taught there: Stefan Niculescu, Tiberiu Olah and Aurel Stroe. He moved to France in 1969 and took French citizenship five years later. Meanwhile, he did what he had come to do: take courses at Darmstadt and Cologne given by the dominant figures in the musical avant-garde (Karlheinz Stockhausen, György Ligeti, Iannis Xenakis, John Cage and Mauricio Kagel), attend festivals and develop his creative work.

This, from the first, was independent and original. It did not change. Through a period not kind to musical adventure he stayed on course, and though the exceptional demands he placed on musicians and organisations meant that performances were infrequent, his music was fairly well documented by recordings, of which the most recent, Intimate Rituals, provides a fitting testament.

Horatiu Radulescu, composer, was born on January 7, 1942. He died on September 25, 2008, aged 66