Augmented triad
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In music, an augmented triad is a triad consisting of two major thirds together with a diminished fourth, which together make up an octave. It is called an augmented triad because the two major thirds together make up an augmented fifth. However, in equal temperament the diminished fourth is enharmonically equivalent to an ordinary major third, and the augmented fifth to a minor sixth.
An example of an augmented triad is A♭ C E, where the interval from E to A♭ is a diminished fourth, and from A♭ to E an augmented fifth.
In just intonation, the interval between two major thirds and an octave, 2/(5/4)2, is 32/25, which is flatter by a septimal kleisma of size 225/224 than the septimal major third with ratio 9/7. While septimal meantone temperament tempers out the septimal kleisma, some other temperaments, for example miracle temperament, do so also, and in all of these temperaments the augmented triad may be identified with a circle of two major and one septimal major thirds, making up an octave.
