THE UPIC SYSTEM
Greek composer Iannis Xenakis (1922–2001) is credited with developing the first widely used system that could turn visual gestures into audio. UPIC was a PC-based system on which the composer drew visual gestures that would control parameters of a newly generated audio file. Xenakis composed several works with the system, including La Legende d''Eer (1977) and Mycenae-Alpha (1978), and it was also used by numerous other composers who worked at CCMIX (originally known as CEMAMU and later as Les Ateliers UPIC), the research center and music studio that Xenakis set up in the suburbs of Paris.
You can find a number of works composed with UPIC on a 2-CD set on Mode Records (CCMIX, available at moderecords.com) and view a visualization of Xenakis''s Mycenae-Alpha at youtube.com/watch?v=yztoaNakKok (also check out the original graphics score that Xenakis created for Metastasis). You''ll find an animated rendition of Gyorgy Ligetti''s famous work Articulations at forbiddenmusic.wordpress.com/2007/10/21/ligeti-on-youtube. Both give a good idea of how a composer might compose using lines, circles, and other graphic images.