Tetrachord

In music theory, a tetrachord (Greek: τετράχορδoν; Latin: tetrachordum) is a series of four notes separated by three intervals.

498 cents)—but in modern use it means any four-note segment of a scale or tone row, not necessarily related to a particular tuning system.

The hypate and mese, and the paramese and nete are fixed, and a perfect fourth apart, while the position of the parhypate and lichanos, or trite and paranete, are movable.

Here are the traditional Pythagorean tunings of the diatonic and chromatic tetrachords: Here is a representative Pythagorean tuning of the enharmonic genus attributed to Archytas: The number of strings on the classical lyre varied at different epochs, and possibly in different localities – four, seven and ten having been favorite numbers.

The 19th-century theorists of ancient Greek music believed that this had also been the case in Antiquity, and imagined that there had existed Dorian, Phrygian or Lydian tetrachords.

[11] Theorists of the later 20th century often use the term "tetrachord" to describe any four-note set when analysing music of a variety of styles and historical periods.

[17] Tetrachords based upon equal-tempered tuning were also used to approximate common heptatonic scales in use in Indian, Hungarian, Arabian and Greek musics.

A more inclusive description (where Ottoman, Persian, and Arabic overlap), of the scale divisions is that of 24 quarter tones (see also Arabian maqam).

It should be mentioned that Al-Farabi's, among other Islamic musical treatises, also contained additional division schemes as well as providing a gloss of the Greek system, as Aristoxenian doctrines were often included.

[24] It is typically a set of harmonic variations in homophonic texture, wherein the bass descends through some tetrachord, possibly that of the previous paragraph, but usually one suggesting a minor mode.

Because of the extreme brevity of the theme and number of repetitions required, and free of the binding of chord progression to tetrachord in the lament, the breadth of the harmonic excursion in litany is usually notable.