Acousmatic music
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 inherently acousmatic, as Lydia Goehr (1999) paraphrases, "the sound world is not a space into which we can enter; it is a world we treat at a distance". Style. Acousmatic music may contain sounds that have recognizably musical sources, but may equally present recognizable sources that are beyond the bounds of traditional vocal and instrumental technology. We are as likely to hear the sounds of a bird, or of a factory as we are the sounds of a violin. The technology involved transcends the mere reproduction of sounds. Techniques of synthesis and sound processing are employed which  may present us with sounds that are unfamiliar and that may defy clear source attribution. Acousmatic compositions may present us with familiar musical events: chords, melodies and rhythms which are easily reconcilable with other forms of music, but may equally present us with events which cannot be classified within such a traditional taxonomy. Performance practice. Acousmatic compositions are sometimes presented to audiences in concert settings that are often indistinguishable from acoustic recitals, albeit without performers. In an acousmatic concert the sound component is produced using pre-recorded media, or generated in real-time using a computer. The sound material  will then be distributed spatially, via multiple loudspeakers, using a practice known as "sound diffusion". The work is often "diffused" by the composer (if present) but the role of interpreter can also be assumed by another practitioner of the art. To provide a guideline for "spatialisation" of the work by an interpreter, many composers provide a "diffusion score"; in its simplest form this might be a graphic representation of the acousmatic work with indications for spatial manipulations, relative to a time-line. The acousmatic experience. In acousmatic music, listeners are challenged to distinguish sounds, not based on their source, but  by their sonic quality. As Pierre Schaeffer writes in his "Treatise on Musical Objects" "The concealment of the causes does not result from a technical imperfection, nor is it an occasional process of variation: it becomes a precondition, a deliberate placing-in-condition of the subject. It is "toward it", then, that the question turns around; "what am I hearing?... What exactly are you hearing" -in the sense that one asks the subject to describe not the external references of the sound it perceives but the perception itself." That music is acousmatic is determined more by "how" it is listened  to, than by whether it is being played from a loudspeaker or not. In understanding the term 'acousmatic' appropriately, it is necessary to distinguish clearly between sound "source" and sound "identity". If for example a recording of a solo cello being played in a recognizable way is sounded through a loudspeaker, the source of the sound is the loudspeaker, but its identity is still 'cello' for a listener. Thus, acousmatic music can be said to be that which calls for the listener to perceive sound without (or with a reduced) sensibility to the sound's identity. The listening mode is  oriented instead upon more abstract timbral than mimetic aspects of the sound. Pierre Schaeffer has referred to this as "écoute réduite" (reduced or narrowed-down listening). It can be said that an "écoute réduite" leads to the perception of music as acousmatic, in the sense that playing sounds from loudspeakers has the potential for obscuring their identity, as the visual reference is removed.