The musical score of The Dark Crystal played a critical role in the film. Music was used not only to underline mood, but since much of the dialogue and action was so cryptic, it was relied on at times to create and sustain dramatic tension.
Jim Henson had been anxious to discover a musician who was young and inventive, who had the necessary experience yet could work with the Henson team in a flexible and experimental way. The producers learned of a young composer, Trevor Jones, who was scoring a John Boorman picture, then called The Knights. (It later became Excalibur.) This was Jones' sixth feature. While attending the National Film School, he had also scored dozens of student movies. He was an innovator – adept at both conventional orchestral scoring and employing synthesizers and other electronic devices. Better still, he was enthusiastic about working with the Dark Crystal team in precisely the freewheeling way Henson had envisioned.
Generally speaking, a score cannot be written until a movie has been edited into its final form (since it must match the visual images precisely). In this case, however, certain scenes had to be scored in advance for very practical reasons. The Pod People's feast, for example, fell into this category because it would be necessary for Brian Froud to hear the music before he could design the instruments that the Pod musicians would play.
For the most part, though, Jones received videotapes of each scene, in a rough cut form, so that he could watch them while he sat at the piano or – more typically – worked with a synthesizer, trying out themes that might later form the basis of the score. The main debate, from the outset, was whether the music should be relatively conventional, so as to make the movie more accessible to audiences, or strange and outlandish, so as to heighten the action on the screen. At first it was agreed that the former approach was correct. However, midway through principal photography, as the completed scenes began to accumulate, it was decided to reverse this decision and to use the music to intensify the strangeness. The completed score was recorded by the London Symphony Orchestra, supplemented by a synthesizer and a variety of unconventional instruments. Jen's twin flute, for instance, is represented on the sound track by an eighteenth-century double-flageolet that Jones came across in a Hampstead music store. The difficulty here was to find a musician who could play it imperfectly enough to match the limited skill that must be presumed for Jen. In Jim Henson's opinion, the results were perhaps the most ambitious fusion of electronic and orchestral music ever recorded for a movie soundtrack.