A number of different sound and image devices would have been needed to present this subject-matter multi-medially in the early 1990s: a slide projector, a video recorder, an audio-cassette tape deck or an audio CD player. A mere decade later this can all be done on a single digital platform, and so can be processed on this website in text, image and sound. The computer as a so-called universal machine replaces a number of individual, separate media apparatuses, it deals with images, sound and text at the same time. So it seems that the difference between image and sound now lies only in different data formats. [2] But when video data are combined with audio data, and vice versa, at the touch of a button [3] —can we say that technology has surmounted all the genre boundaries, and can we see the multi-media universal work of art as something we can take for granted? Hardly. So before we get to art, here are a few fundamental thoughts.

Perception—physics—art

Let us not be deceived by the media technology of the universal machine: image and sound are completely

separate physical phenomena. Sound wave are vibrations in the air, which is why airless outer space is so silent. Light is our name for the small proportion of the electromagnetic spectrum that is visible to man. The full range of the spectrum ranges from kitchen microwaves to long wave radio transmitters. Put loosely: these phenomena are as alien to each other as a horse and a motorbike.

There is only one place in the world where light and sound affect each other mutually in a way that goes well beyond any technology or physics: in human perception. This is where the synaesthesia of sound and vision comes into being. It becomes an artistic experience, a state of audio-visual 1 intoxication and almost religious ecstasy. Torch dances in primeval caves, organ music in the light of Gothic stained-glass windows, Baroque firework music, Wagner's operas, psychedelic rock concerts, techno-parties—all these indulge our synaesthetic delight in audio-visions [4] (cf. text by Barbara John).

Mankind has been searching for a natural law on the relationship between colours and sounds for millennia. But no objective links can be established