Acousmatic music is a form of electroacoustic music that deals specifically with acousmatic sound as a compositional resource. The practice has a historical basis in musique concrète. It can be created using non-acoustic technology, exists only in a recorded format (as a fixed medium), and is composed for reception via loudspeakers. The compositional material is not restricted to the inclusion of sonorities derived from musical instruments or voices, nor to elements traditionally thought of as ‘musical’ (melody, harmony, rhythm, metreand so on), but rather admits any sound, acoustic or synthetic. With the aid of various technologies, such as tape recorders, digital signal processing tools and digital audio workstations, this material can then be combined, juxtaposed, and transformed, in any conceivable manner. In this context the compositional method can be seen as a process of sound organisation: a term first used by the French composer Edgard Varèse.
(Taken from wikipedia).