Major and minor
The third distinguishes major from minor. A major third reaches clockwise to M3. A minor third stops one step earlier at m3.
Chord qualities as interval shapes
Each chord is a polygon on the 12-tone circle. In Relative mode, the root sits at the top, so chords of the same quality share a shape. In Absolute mode, the ring shows fixed pitch classes with C at the top. The polygon rotates to the chord's actual notes. The bass / inversion control changes naming and playback order but leaves the shape unchanged. Harmony Engine extends these shapes to voice leading and phrase-planned progressions.
Visual key: the ring shows all 12 pitch classes. Red marks the root, black marks selected notes, and the shaded polygon shows the chord.
Pitch labels
Wheel order
Chord Details
Intervals above root
Stack from bass
Bass
Recognized root
Symbol
Semitones above root
Forte prime form
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Interval-class vector
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Chord Quality
Play
Sonority (Plomp-Levelt / Sethares)
The plot estimates sensory dissonance, the roughness caused by nearby frequencies. It uses the Plomp-Levelt curve (1965), as refined by Sethares (1993). Each note contains its fundamental frequency and six harmonics. Harmonic n has amplitude 1/n. Vertical lines mark the chord intervals above the bass.
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Key fit (Krumhansl-Kessler)
Each key profile assigns a typical stability value to all 12 pitch classes. The chart correlates the selected chord with the 24 major and minor profiles from Krumhansl and Kessler (1982). The outer ring shows major keys. The inner ring shows minor keys. Dot size shows correlation. The center names the strongest match.
— average stability rating for each scale step (chord tones highlighted)
Common chords
Reading the shapes
Root and bass
The red P1 is the reference note. The recognizer can choose another selected tone as the chord root; the bass is the lowest played tone.
Suspensions
A suspended chord removes the third. The replacement tone is either M2 or P4. The resulting shape has no major or minor third.
Altered fifths
Augmented and diminished chords move the fifth by one semitone. That shifts the triangle point from P5 to m6 or TT.
Sevenths
Four-note chords become quadrilaterals. The spacing among the third, fifth, and seventh distinguishes dominant, minor, major, and diminished seventh chords.
Tonic
Tonic is a key function, not a chord tone. The controls name roots and bass notes without assigning a key center.