9:8 · 2 semitones
Major second. Two pure ratios, one key: billed 4 cents against one and 18 against the other.
- Pure
- 203.91¢
- Tempered
- 200¢
- Charge
- −3.91¢
- Beat
- 0.56 Hz
- Charge vs 10:9
- +17.60¢
- Beat vs 10:9
- 2.50 Hz
Lower note 220 Hz. Pure upper 247.50 Hz. Tempered upper 246.94 Hz.
Every other interval here has one pure ratio. The whole tone has two. The major tone is 9:8; the minor tone is 10:9. Just tuning uses both, and they differ by exactly one syntonic comma, 81:80, about 21.5 cents. The keyboard has one whole tone, 200 cents, and bills it against both.
Against 9:8 the charge is −3.91 cents, small. Against 10:9 it is +17.60, bigger than the major third's. Which one you are being billed against depends on where the note sits in the scale; the ledger lists 9:8 and shows 10:9 beside it. On a 220 Hz lower note the tempered tone beats against pure 9:8 at 0.56 Hz and against pure 10:9 at 2.50 Hz; "both" plays 9:8 with tempered, and the 10:9 buttons play the other. Sizes from Major second (Wikipedia, CC BY-SA).