Petrmic chords
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Petrmic chords are essentially tempered dyadic chords tempered by the petrma, 2200/2197.
The petrmic triad is a palindrome in the 2.5.11.13 subgroup 13-odd-limit, consisting of two 13/10 intervals followed by a 13/11, closing at the octave. In other words:
- 1-13/10-22/13 with steps 13/10-13/10-13/11.
It can be extended to the following palindromic tetrad:
- 1-11/10-13/10-22/13 with steps 11/10-13/11-13/10-13/11
Equal temperaments with petrmic chords include 29, 37, 50, 53, 58, 84, 87, 111, 121, 140, 190, 198, 224, 311, 414, 422, and 612. 37, 50 and especially 29 have notably good petrmic triads.