20:25:30:36
| Chord information |
20:25:30:36, a major-minor seventh chord, is a tetrad in 5-limit harmony, and sometimes considered a form of dominant seventh chord. It combines a 5/4 major third with the consonant 9/5 seventh that would be found in a Ptolemaic minor seventh chord on the same root, creating a 36/25 tritone between the two.
The major-minor seventh chord is found rooted at the I (1⁄1) and IV (4⁄3) of the duodene.
In the meantone tuning of this chord, the ~9/5 seventh is equated with ~16/9, making it equivalent to the meantone tuning of 36:45:54:64.
In the septimal meantone tuning of this chord, the ~36/25 tritone is equated with the more consonant interval 10/7, and the major-minor seventh chord becomes an essentially tempered chord in the 9-odd-limit.