The DJs and laptop performers of electronic dance music (EDM) use preexistent elements such as vinyl records and digital samples to create fluid, dynamic performances. These performances are also largely improvised, evolving in response to the demands of a particular situation through interaction with a dancing audience.
In performance, musicians make numerous spontaneous decisions about variables such as which sounds they will play, when they will play them, and how they will be combined with other sounds. Yet the elements that constitute these improvisations are also fixed in certain fundamental ways: Performances are fashioned from patterns or tracks recorded beforehand, and, in the case of DJ sets, these elements are also physical objects (vinyl records).
This according to Playing with something that runs: Technology, improvisation, and composition in DJ and laptop performance by Mark J. Butler (New York: Oxford University Press, 2014).
Above and below, “The Wizard” Jeff Mills, who provides a case study in the book.
BONUS: Mr. Mills performs in 2016.