Avant-garde composers criticized the predominant use of electronic instruments for conventional purposes.[16] The instruments offered expansions in pitch resources[18] that were exploited by advocates of microtonal music such as Charles Ives, Dimitrios Levidis, Olivier Messiaen and Edgard Varse.[19][20][21] Further, Percy Grainger used the theremin to abandon fixed tonation entirely,[22] while Russian composers such as Gavriil Popov treated it as a source of noise in otherwise-acoustic noise music.[23]