Circle Of Thirds

Circle of Thirds is a music theory app for exploring chords, scales, and intervals on a circular diagram. The seven notes of the scale sit at fixed positions around the circle, so you can see how chords relate to each other as you play them. Tap a note to play a chord built from the current scale. Pick a chord shape, change the mode, swipe a chord to move it through a voicing.

MODES AND SCALES Pick major or minor. The major mode uses the major scale. The minor mode combines the natural and harmonic minor: the 7th degree sharpens dynamically when you play a chord on the 5th degree, so common minor progressions like i–VII–VI–V work as expected. Melodic minor is included by default.

The scale uses seven fixed letter names, with accidentals that update based on the mode you pick. Changing the root rotates the seven notes so each scale degree always stays in the same position on the circle.

CHORD TYPES Triads, 7ths, 9ths, sus2 / sus4, add chords, inversions, gap chords. The same chord shape gives different qualities depending on the degree: a "7th" can produce a major 7th, a dominant 7th, a half-diminished, and so on, all built from the pitches in the scale.

PIN CHORDS TO THE CIRCLE Tap "+" to pin the current chord type as a small floating button. Drag a button to a different note to change its root. Special buttons cover secondary dominants, parallel triads, and other tonicizations.

INTERVALS Active notes are connected by labeled interval lines (P5, M3, d4, m2, and so on). Each interval type can be toggled on or off, with separate colors for the more dissonant ones.

INPUT Tap the circle, tap the piano keyboard below it, or plug in a MIDI device. Chord detection figures out the likeliest enharmonic spelling from context, since the same piano key can be B#, C, or Dbb depending on the key and chord.

VOICE LEADING The auto-voicer keeps common tones between chords and moves the rest by the smallest step. Swipe a played chord up or down to push the bass higher or lower, or sideways to spread the top voices.

PRO (one-time purchase) A one-time Pro purchase unlocks: • Chord Bank: save chords and recall them with a tap • Advanced voice leading: bias direction, automatic inversions, smoothing • MIDI Out: send chords and notes to an external synth or DAW • Alternate circle layouts: thirds, fifths, seconds • More scales: harmonic major, neapolitan, gypsy, and other exotic modes • Background themes: custom colors and gradients

Free users get 20 voice-leading swipes per day to try the feature.

This app is subject to Apple's standard EULA: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/