Italian sixth chord
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An Italian sixth chord is a triad comprising a root, major third, and augmented sixth.
In meantone
In 5-limit meantone, the traditional foundation of tonal harmony, the augmented sixth represents both 225/128 and 125/72. It is treated as a rare and special dissonance, especially when used on the sixth degree. The 5-limit meantone Italian sixth chord,
- (Meantone) 1 – 5/4 – 125/72
simultaneously represents both 72:90:125 (with steps 5/4 and 25/18) and 128:160:225 (with steps 5/4 and 45/32).
However, in the historically prevalent quarter-comma meantone, the augmented sixth is tuned only a few cents shy of a just 7/4, so the meantone Italian sixth chord can be considered to approximate the septimal meantone chord:
- (Septimal meantone) 1 – 5/4 – 7/4
representing 4:5:7 (with steps 5/4 and 7/5).
In just intonation
In the 5-limit:
- 128:160:225, one of the possible 5-limit interpretations of the meantone chord, is found rooted at ♭II (16⁄15) and ♭VI (8⁄5) in the duodene.