When György Ligeti was a child he had a recurring dream. In it, a vast network of tangled fibres hung around his bed; even the smallest movement would cause the whole structure to shudder and pulsate. Related many years later, this core memory has become a popular analogy for what the composer called ‘micropolyphony’ – music made up of many individual lines, each moving at different speeds and by varying degrees, combining to create a shimmering cluster of sound …