Scores: Universal Edition, 1979; revised version 2003

Issues of pulse have inevitably been prominent in a book relating to music of the twentieth and twenty-first centuries. It has also been stressed that subjective artistry should never be absent from any technical mechanism required for interpretation and performance. Nonetheless, there is a further dimension to analyse in relation to pulse itself. In Part One the music of several composers illustrates varying applications of metric modulation. An extreme experiment with this feature is made by Harrison Birtwistle in what could be described as a pulse piece. His Silbury Air makes very exacting, but very exciting demands on a conductor. There are two versions of the work: the original dating from 1979 and a revised one from 2003. Both editions are required for reference; I shall refer to the 1979 version as A, the 2003 as B. In A there is a unique graphic characteristic which identifies the number of beats in any bar by a single integer, while the quality of the units is signified by a time-signature. B simplifies the complex irregularity of pulse by using conventional notation. Comparing pp. 1 and 2 in each version exposes a number of varying features. Throughout B Birtwistle has chosen to revise some of the orchestration and to recompose certain sections. While the revised version B must now be used in performance, I consider it to be essential for a conductor to study version A because its structural relation to the pulse labyrinth, printed as a glossary in both versions, is more identifiable with the composition process than version B.

From a composer’s point of view, version A contains a fascinating logic which a conductor will also find useful in gaining an insight into the motivation behind Birtwistle’s idea. He describes the substance as ‘invested logic via modes of juxtaposition, modes of repetition, modes of change’. The pulse labyrinth sets out the metric modulation relationships. In version B Birtwistle explains that this is included to indicate the ‘compositional logic’ rather than an aid for conductors. I maintain that the labyrinth is an essential part of the conductor’s comprehension of the music.