Listen to a sample of Gerard Grisey's Spectralist music

If you’ve ever thought of doing a spot of classical composition, here are a few tips. Ditch your pencil, paper and piano. Purchase one very large, powerful computer. Find one equally large, powerful new brain. Replace for your own. And get printing. For there’s a new musical lingua franca and it relies on indescribably complicated computer printouts (spectrograms), wave analysis and new Pythagoreanism. Don’t ask. What really matters is that it’s called Spectralism, it’s the future of classical music — and it actually sounds rather nice.

Out of the fog of avant-garde schools — New Complexity, New Simplicity, Neoromanticism, Minimalism — the 1970s French Spectralist movement has in the past decade come to the fore. This season the Southbank Centre in London showcases the work of this school with a rare performance by the London Sinfonietta of Gérard Grisey’s Les Espaces Acoustiques at the Queen Elizabeth Hall, and a composer day in February dedicated to Tristan Murail, a leading Spectralist member.

“It’s music actually made from very simple materials,” says George Benjamin, who will conduct the Grisey. “The listener stands back and hears these materials in a hypnotic fashion gradually transforming from one state to another, almost in a psychedelic way.”

It all seems a long way from Mozart. But, fundamentally, it isn’t. Beneath the computers and the jargon, Spectralism was a simplifying movement, just like Mozart’s Classicism. Both were reactions to decades of musical overcomplication. In Mozart’s youth this was exemplified by the warren-like fugues of high Baroque; in Grisey and Murail’s the unpopular abstractions of Serialism that lifted mathematical equations to a musical art form.

While the Serialists built up ever loftier and more fantastically ornate structures, the French Spectralists looked to the psychedelic sounds of Pink Floyd’s Dark Side of the Moon.

It was a complicated process. And expensive. Only two musical institutions in the world had the technology to do the computer analysis that the Spectralists sought: Stanford University and the Institut de Recherche et Coordination Acoustique/Musique in Paris.

Spectralists were trying to access a sonic rainbow, one that lurked naturally within each and every sound. Just like the spectrum of colours that makes up white light, a spectrum of faint noises makes up each and every sound. This became the Spectralists’ new scale.

Before devising each piece of music, a composer would feed a computer a note, say the sound of a bell or a violin, and a programme would unravel it, revealing a spectrum of pitches, showing up as coloured lines on a graph. The composer would then take each of these pitches and get each part of the orchestra to reconstitute the original sound.

The first to use this sonic spectrum was Grisey, who in 1974 began composing Les Espaces Acoustiques. It did more than introduce a new sonic landscape, however. In Les Espaces Grisey reintroduced many of the traditional principles of composition that the previous generation had tried to strangle and bury. Tonality, rhythmic pulse, predictability — and the idea that harmoniousness was pleasant on the ear and that dissonance wasn’t — were all back. In the first bars, Grisey even includes a tune that you could whistle. “It really was quite significant,” the composer Julian Anderson explains. “It would have been almost impossible to whistle a piece of Serialism with any ease.”

The movement gained traction as foreign composers passed through Paris during the 1980s and took in the movement’s exotic ways: its colours, directness and, as Anderson vividly remembers, those spectacular computer printouts. “You can’t imagine how exciting it was to see those printouts for the first time.”

The music itself had an undeniably winning formula, ricocheting between the harmonious and the noisy, the familiar and the unfamiliar; it was refreshingly intelligible stuff without being overly simplistic. In Les Espaces the music moves slowly and smoothly from one pole to the other like some great sea.

One drawback, however, was the typical avant-gardish fragility of the movement. Grisey was uneasy with the tag of Spectralism and totally against the creation of a “school”. So while many of the world’s most important contemporary composers — Kaija Saariaho, Magnus Lindberg, Peter Eötvös, Julian Anderson, Jonathan Harvey, Ligeti — all absorbed its language, most left labels behind. The result was that other more unashamedly populist rivals such as the Minimalists began to steal a march on the movement.

But, surreptitiously, spectrally, the movement’s techniques began to seep into composers’ works, on to music faculties and universities across Europe and America. What cemented Spectralism’s place as the new musical tongue, however, was computers. Tristan Murail says: “When you compose computer music it’s inevitable that you’ll use Spectral techniques because you’re creating sounds from scratch. So fewer and fewer composers began to see a difference between Spectralism and computer music.”

For many decades now it has been fashionable to argue that the narrative of classical music was choked with Modernism, that the thread from church monophony to total Serialism had been severed, the story shattered. That for ever more a messy, amorphous Postmodernism would reign. Well, perhaps not. While many composers aren’t yet in thrall to its ways, Spectralism seems likely to dominate contemporary classical music in a way that none has for a very long time. “I think its time will come,” Anderson says. “And I think it’s coming right now.”

Les Espaces Acoustiques, October 14, Queen Elizabeth Hall. londonsinfonietta.org.uk

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