s in addition to
‘uninflected’ notes from A to G, and so differs from the later diatonic system
(see also Musica ficta).(from Gk. dia tonos: ‘proceeding by whole tones’).
Based on or derivable from an octave of seven notes in a particular configuration, as opposed to Chromatic and other forms of Scale. A seven-note scale is said to be diatonic when its octave span is filled by five tones and two semitones, with the semitones maximally separated, for example the major scale (T–T–S–T–T–T–S). The natural minor scale and the church modes (see Mode) are also diatonic.
An interval is said to be diatonic if it is available within a diatonic scale. The following intervals and their compounds are all diatonic: minor 2nd (S), major 2nd (T), minor 3rd (TS), major 3rd (TT), perfect 4th (TTS), perfect 5th (TTST), minor 6th (STTTS), major 6th (TTSTT), minor 7th (TSTTTS), major 7th (TTSTTT) and the octave itself. The Tritone, in theory diatonic according to this definition, has traditionally been regarded as the alteration of a perfect interval, and hence chromatic; it may be either a semitone more than a perfect 4th (augmented 4th: TTT) or a semitone less than a perfect 5th (diminished 5th: STTS).
In the ancient Greek system (see Tetrachord), the diatonic genus contains a semitone and two tones (STT). Although this does not amount to a complete octave species, it nevertheless retains the basic sequence of tones and semitones given above.
Similarly,
each Hexachord in the medieval system as codified by
Guido of Arezzo includes a semitone surrounded by two tones (TTSTT) and was
therefore diatonic by the above definition. However, since it is built of
overlapping hexachords on G, C and F, the Guidonian gamut includes several Bs in addition to
‘uninflected’ notes from A to G, and so differs from the later diatonic system
(see also Musica ficta).
WILLIAM DRABKIN/R