Diatonic and chromatic

Diatonic and chromatic are terms in music theory that are most often used to characterize scales, and are also applied to musical instruments, intervals, chords, notes, musical styles, and kinds of harmony. They are very often used as a pair, especially when applied to contrasting features of the common practice music of the period 1600–1900. These terms may mean different things in different contexts. Very often, diatonic refers to musical elements derived from the modes and transpositions of the "white note scale" C–D–E–F–G–A–B. In some usages it includes all forms of heptatonic scale that are in common use in Western music (the major, and all forms of the minor). Chromatic most often refers to structures derived from the twelve-note chromatic scale, which consists of all semitones. Historically, however, it had other senses, referring in Ancient Greek music theory to a particular tuning of the tetrachord, and to a rhythmic notational convention in mensural music of the 14th to 16th centuries. Genus (music) In ancient Greece there were three standard tunings (known by the Latin word genus, plural genera) of a lyre. These three tunings were called diatonic, chromatic, and enharmonic, and the sequences of four notes that they produced were called tetrachords ("four strings"). A diatonic tetrachord comprised, in descending order, two whole tones and a semitone, such as A G F E (roughly). In the chromatic tetrachord the second string of the lyre was lowered from G to G, so that the two lower intervals in the tetrachord were semitones, making the pitches A G F E. In the enharmonic tetrachord the second string of the lyre was lowered further to G, so that the two lower interval in the tetrachord were quarter tones, making the pitches A G F E (where F is F lowered by a quarter tone). For all three tetrachords, only the middle two strings varied in their pitch. The term cromatico (Italian) was occasionally used in the Medieval and Renaissance periods to refer to the coloration (Latin coloratio) of certain notes.