Acousmatic music (from Greek ἄκουσμα akousma, "a thing heard") is a form of electroacoustic music that is specifically composed for presentation using speakers, as opposed to a live performance. It stems from a compositional tradition that dates back to the introduction of musique concrète (a form of musique expérimentale) in the late 1940s. Unlike musical works that are realised using sheet music exclusively, compositions that are purely acousmatic (in listening terms) often exist solely as fixed media audio recordings. The compositional practice of acousmatic music features acousmatic sound as a central musical aspect. Other aspects traditionally thought of as 'musical' such as melody, harmony, rhythm, metre may be present but more often consideration is given to sound-based characteristics such as timbre and spectrum. Compositional materials can include sounds derived from musical instruments, voice, electronically generated sound, audio that has been manipulated using various effect processors, as well as general sound effects and field recordings. The music is produced with the aid of various music technologies, such as digital recorders, digital signal processing tools and digital audio workstations. Using such technology various sound materials can 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. Origins According to certain historical accounts, the origin of the term acousmatic can be traced back to Pythagoras; the philosopher is believed to have tutored his students from behind a screen so as not to let his presence distract them from the content of his lectures. Under these conditions, the listener focuses on the sounds being produced to heighten the sense of hearing. In 1955, Jérôme Peignot and Pierre Schaeffer were the first to use the term acousmatique to define the listening experience of musique concrète. It is said to be derived from akousmatikoi, the outer circle of Pythagoras' disciples who only heard their teacher speaking from behind a veil. In a similar way, one hears acousmatic music from behind the 'veil' of loudspeakers, without seeing the source of the sound. Developments Within academia the term acousmatic music, or acousmatic art, has gained common usage, particularly when referring to contemporary musique concrète; however, there is some dispute as to whether acousmatic practice relates to a style of composition or a way of listening to sound. Scruton defines the experience of sound as