Riley's music is usually based on improvising through a series of modal figures of different lengths. Works such as "In C" (1964) and the "Keyboard Studies" (1964–1966) demonstrate this technique. The first performance of "In C" was given by Steve Reich, Jon Gibson, Pauline Oliveros and Morton Subotnick. Its form was an innovation: The piece consists of 53 separate modules of roughly one measure apiece, each containing a different musical pattern but each, as the title implies, in the key of C. One performer beats a steady pulse of "C"s on the piano to keep tempo. The others, in any number and on any instrument, perform these musical modules following a few loose guidelines, with the different musical modules interlocking in various ways as time goes on.