The name UR belongs to the ancient Sumerian town, and to a Swedish word with many meanings. It corresponds to the English preposition of, and is used as a prefix (in German as well) in many words expressing something extreme or original, also primitive. But it also has the meaning of a clock or a tempest. UR was commissioned by IRCAM and premiered by the Ensemble InterContemporain, in connection with IRCAM's Symposium on Personal Systems for Computer Music (October 1986).
The instrumental and computer parts are written using calculations of rhythms and harmonies programmed in LeLisp on the Macintosh. Formalization of rules for the automatic creation of rhythmic events, gestures, and temporal processes in the piece is relatively straightforward. Defining a similar environment for processing harmonies and chains of chords is more complex. To get musically more coherent results I created a model of rules, set up as a field of accepted qualities for chords, to formalize processing of harmonies.
The microcomputer is also used in performance to control MIDI instruments; the score is organized as a set of sequences for the computer part, being triggered in real time by the pianist during the performance. Every time the pianist passes a keystroke form a MIDI-keyboard to the computer, combinations of precomposed chord-sequences, rhythm patterns, articulation shapes, etc., are generated in real time and played immediately by the Yamaha TX-816 synthesizer. This allows a very flexible way of organizing synchronization between live performers and computer without the use of a click-track.
Performance software was implemented in PreForm by Lee Boynton.