Diatonic and chromatic are terms in music theory that are used to characterize scales. The terms 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 chromatic scale in 12-tone equal temperament, 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.
History
Greek genera
In ancient Greece there were three standard tunings (known by the Latin word genus, plural genera) of a lyre.It is unclear whether the lyre in question was itself a presumed four-stringed instrument ("τετράχορδον ὄργανον"), as some have suggested (see Peter Gorman, Pythagoras, a Life (London: Routledge & K. Paul, 1979), p. 162: "The fundamental instrument of early Greek music was the tetrachord or four-stringed lyre, which was tuned in accordance with the main concordances; the tetrachord was also the foundation of Greek harmonic theory"). The number of strings on early lyres and similar instruments is a matter of much speculation (see Martin Litchfield West, Ancient Greek music (Oxford and New York: Oxford University Press, 1994), especially pp. 62–64). Multiple later instruments had seven or perhaps more strings, and in that case the tetrachord must be thought of as based on a selection of four adjacent strings. These three tunings were called diatonic, chromatic, and enharmonic,Occasionally, as in the Rollin excerpt shown in this section, spelt inharmonic; but in OED this is only given as a distinct word with a distinct etymology ("Not harmonic; not in harmony; dissonant,..."). The motivation and sources of the Greek term ἐναρμονικός (enarmonikós) are little understood. But the two roots are ἐν (en: "in") and ἁρμονία (harmonía: "good placement of parts", "harmony", "a scale, mode, or τόνος [in one sense; see notes above]"). So in some way the term suggests harmoniousness or good disposition of parts, but not in the modern sense of harmony, which has to do with simultaneous sounds. (See Solon Michaelides, The Music of Ancient Greece: An Encyclopaedia (London: Faber and Faber, 1978); Liddell and Scott; etc.) For more information, especially concerning the various exact tunings of the enharmonic tetrachord, see Enharmonic genus. 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.
Medieval coloration The term cromatico (Italian) was occasionally used in the medieval and Renaissance periods to refer to the coloration (Latin coloratio) of certain notes. The details vary widely by period and place, but generally the addition of a colour (often red) to an empty or filled head of a note, or the "colouring in" of an otherwise empty head of a note, shortens the duration of the note. In works of the Ars Nova from the 14th century, this was used to indicate a temporary change in metre from triple to duple, or vice versa. This usage became less common in the 15th century as open white noteheads became the standard notational form for minims (half-notes) and longer notes called white mensural notation.Parrish, Carl, The Notation of Medieval Music, Pendragon, New York, 1978, pp. 147ff.Harvard Dictionary of Music, 2nd ed., "Chromatic". Similarly, in the 16th century, a form of notating secular music, especially madrigals in was referred to as "chromatic" because of its abundance of "coloured in" black notes, that is semiminims (crotchets or quarter notes) and shorter notes, as opposed to the open white notes in , commonly used for the notation of sacred music. These uses for the word have no relationship to the modern meaning of chromatic, but the sense survives in the current term coloratura."The root of the Italian term is that of 'colour', and it is probably related through its use of diminution (the little notes that 'rush' to the next long note, as Bernhard writes) to the mensural practice of coloration" (New Grove, "Coloratura").
Renaissance chromaticism
The term chromatic began to approach its modern usage in the 16th century. For instance Orlando Lasso's Prophetiae Sibyllarum opens with a prologue proclaiming, "these chromatic songs,Rendered by many as Carmina chromatico, though this is incorrect Latin; the title is given as Carmina chromatica (which is plural of Latin carmen chromaticum) in New Grove Online. The entire passage is relevant to present points in this article: heard in modulation, are those in which the mysteries of the Sibyls are sung, intrepidly," which here takes its modern meaning referring to the frequent change of key and use of chromatic intervals in the work. (The Prophetiae belonged to an experimental musical movement of the time, called musica reservata). This usage comes from a renewed interest in the Greek genera, especially its chromatic tetrachord, notably by the influential theorist Nicola Vicentino in his treatise on ancient and modern practice, 1555.
Diatonic scales
Medieval theorists defined scales in terms of the Greek tetrachords. The gamut was the series of pitches from which all the Medieval "scales" (or modes, strictly) notionally derive, and it may be thought of as constructed in a certain way from diatonic tetrachords. The origin of the word gamut is explained in the article Guidonian hand; here the word is used in one of the available senses: the all-encompassing gamut as described by Guido d'Arezzo (which includes all of the modes).
The intervals from one note to the next in this medieval gamut are all tones or semitones, recurring in a certain pattern with five tones (T) and two semitones (S) in any given octave. The semitones are separated as much as they can be, between alternating groups of three tones and two tones. Here are the intervals for a string of ascending notes (starting with F) from the gamut: ... –T–T–T–S–T–T–S–T–T–T–S–T– ... And here are the intervals for an ascending octave (the seven intervals separating the eight notes A–B–C–D–E–F–G–A) from the gamut: T–S–T–T–S–T–T (five tones and two semitones)
The white keys are the modern analog of the gamut. In its most strict definition, therefore, a diatonic scale is one that may be derived from the pitches represented in successive white keys of the piano (or a transposition thereof). This would include the major scale, and the natural minor scale (same as the descending form of the melodic minor), but not the old ecclesiastical church modes, most of which included both versions of the "variable" note B/B.
Modern meanings There are specific applications in the music of the Common Practice Period, and later music that shares its core features.
Most, but not all writers,Goetschius, as cited below, accepts only the major as diatonic. accept the natural minor as diatonic. As for other forms of the minor:
"Exclusive" usage Some writers consistently classify the other variants of the minor scale – the melodic minor (ascending form) and the harmonic minor – as non-diatonic, since they are not transpositions of the white-note pitches of the piano. Among such theorists there is no agreed general term that encompasses the major and all forms of the minor scale. "Inclusive" usage Some writers consistently include the melodic and harmonic minor scales as diatonic also. For this group, every scale standardly used in common practice music and much similar later music is either diatonic (the major, and all forms of the minor) or chromatic. "Mixed" usage Still other writers mix these two meanings of diatonic (and conversely for chromatic), and this can lead to confusions and misconceptions. Sometimes context makes the intended meaning clear.
Some other meanings of the term diatonic scale take the extension to harmonic and melodic minor even further, to be even more inclusive.An explicit example of such an extended general use of diatonic scale and related terms: See also #Extended pitch selections, in this article. See also an exceptional usage by Persichetti, in a note to #Diatonic_pentatonic_scale, below.
In general, diatonic is most often used inclusively with respect to music that restricts itself to standard uses of traditional major and minor scales. When discussing music that uses a larger variety of scales and modes (including much jazz, rock, and some tonal 20th-century concert music), writers often adopt the exclusive use to prevent confusion.
Chromatic scale
Chromatic scale on C: full octave ascending and descending
A chromatic scale consists of an ascending or descending sequence of pitches, always proceeding by semitones. Such a sequence of pitches is produced, for example, by playing all the black and white keys of a piano in order. The structure of a chromatic scale is therefore uniform throughout—unlike major and minor scales, which have tones and semitones in particular arrangements (and an augmented second, in the harmonic minor).It is not usual to use chromatic scale in any other sense. A rare exception is found in Elements of Musical Composition, Crotch, William, 1830. (See the quotation from this text, below. See also extensive analysis in the excerpt from "The leading tone in direct chromaticism: from Renaissance to Baroque", Clough, John, 1957, in the same subsection below.) Outside of music altogether, chromatic scale may refer to Von Luschan's chromatic scale.
Musical instruments Some instruments, such as the violin, can play any scale; others, such as the glockenspiel, are restricted to the scale to which they are tuned. Among this latter class, some instruments, such as the piano, are always tuned to a chromatic scale, and can be played in any key, while others are restricted to a diatonic scale, and therefore to a particular key. Some instruments, such as the harmonica, harp, and glockenspiel, are available in both diatonic and chromatic versions (although it is possible to play chromatic notes on a diatonic harmonica, they require extended embouchure techniques, and some chromatic notes are only usable by advanced players).
Intervals
Because diatonic scale is itself ambiguous, distinguishing intervals is also ambiguous. For example, the interval B–E (a diminished fourth, occurring in C harmonic minor) is considered diatonic if the harmonic minor scale is considered diatonic, but chromatic if the harmonic minor scale is not considered diatonic.
Forte lists the chromatic intervals in major and natural minor as the augmented unison, diminished octave, augmented fifth, diminished fourth, augmented third, diminished sixth, diminished third, augmented sixth, minor second, major seventh, major second, minor seventh, doubly diminished fifth, and doubly augmented fourth.