The R42 Transform
R42 on C, voice by voice: the chords it pairs, the voice that steps, the source's own words, and every chord each side spells.
On C, R42 pairs Cmaj7 (C E G B) with Am7 (A C E G): 1 voice steps, 3 hold, and the lead costs 2 semitones.
| Voice | Becomes | Step |
|---|---|---|
| C | C | holds |
| E | E | holds |
| G | G | holds |
| B | A | -2 |
What each side spells
- Cmaj7: Cmaj7
- Am7: C6, Am7
The paper's printed cycle through all 51 chords takes this step 5 times.
As the source prints it
The most parsimonious transformations exchange two types of sevenths moving just a note by a semitone or a whole-tone.
R42 : [x, x + 4, x + 7, x + 11] ↔ [x, x + 4, x + 7, x + 9]
— A Generalized Dual of the Tonnetz for Seventh Chords: Mathematical, Computational and Compositional Aspects, pp. 301–308; Sonia Cannas and Moreno Andreatta. The source, read 2026-10-25.
Rank every pairing of Cmaj7 and Am7 in the calculator · Every chord one voice from Cmaj7