Xenharmonic music is that which uses a tuning system which neither conforms to nor closely approximates the common 12-tone equal temperament. The term xenharmonic was coined by Ivor Darreg, from xenia, "hospitable," and xenos "foreign." He stated it as being "intended to include just intonation and such temperaments as the 5-, 7-, and 11-tone, along with the higher-numbered really-microtonal systems as far as one wishes to go." John Chalmers, author of Divisions of the Tetrachord, writes: "The converse of this definition is that music which can be performed in 12-tone equal temperament without significant loss of its identity is not truly microtonal." Thus xenharmonic music may be distinguished from the more common twelve-tone equal temperament, as well as some use of just intonation and equal temperaments, by the use of unfamiliar intervals, harmonies, and timbres. Theorists other than Chalmers consider xenharmonic and non-xenharmonic to be subjective. As an example, Edward Foote, in his program notes for his "6 degrees of tonality" CD, refers to the differences in his response to the more radical tunings he uses, such as Kirnberger and DeMorgan, from "shocking", to "Too subtle to immediately notice", saying:
Diatonic xenharmonic music
Music also can share much of the familiar territory of twelve tone music and yet have xenharmonic features. As examples, Easley Blackwood, author of The Structure of Recognizable Diatonic Tunings, wrote many etudes in ETs from 12 equal to 24 equal which bring out both many connections and resemblances to twelve tone music as well as bringing out various xenharmonic characteristics of the tunings. See his Twelve Microtonal Etudes for Electronic Music Media. In his program notes for his Fanfare in 19-et, he writes: For a perhaps more radical example, for his sixteen notes Andantino, he writes: Darreg explains: "I devised the term 'xenharmonic' to refer to everything that does not sound like 12-tone equal temperament."
Tunings, instruments, and composers
Any scale or tuning other than 12-tone equal temperament can be used to create xenharmonic music. This includes other equal divisions of the octave and scales based on extended just intonation. Tunings derived from the partials or overtones of physical objects with an inharmonic spectrum or overtone series such as rods, prongs, plates, discs, spheroids and rocks are sometimes used as the basis of xenharmonic exploration. William Sethares is a pioneer in this area. William Colvig, who worked with the composerLou Harrison created the tubulong, a set of xenharmonic tubes. Electronic music composed with arbitrarily chosen xenharmonic scales was explored on the albumRadionics Radio: An Album of Musical Radionic Thought Frequencies by British composer Daniel Wilson, who composed his pieces with frequency-runs submitted by users of a custom-built web application replicating radionics-based electronic soundmaking equipment used by Oxford's De La Warr Laboratories in the late 1940s. The Non-Pythagorean scale utilized by Robert Schneider of The Apples in Stereo, based on a sequence of logarithms, may be considered xenharmonic, as well as Annie Gosfield's purposefully "out of tune" sampler based music using non systematic tunings and the work of other composers including Elodie Lauten, Wendy Carlos, Ivor Darreg, Paul Erlich and many others.
