The Tetrachord Toolkit

Build from two halves

Pick a Key (the root), then choose a lower and an upper tetrachord from five building blocks:

• Major [2 2 1]
• Minor [2 1 2]
• Upper Minor [1 2 2]
• Harmonic [1 3 1]
• Lydian [2 2 2]

The two halves, joined by a whole step, close the octave. Combine them and you get named scales:

• Major + Major = Ionian (the major scale)
• Upper Minor + Upper Minor = Phrygian
• Lydian + Major = Lydian

That last building block, the Lydian tetrachord, earns its place because Lydian + Lydian builds the whole-tone scale — something none of the others can make. (The naming follows common-practice convention: “Upper Minor,” not “Phrygian tetrachord.”)

Parallel and relative

Two buttons move you between related scales the way the wheel’s spaces do:

• Parallel keeps the root and changes the flavor (C major → C minor).
• Relative keeps the notes and moves the root (C major → A minor).

Stepping the modes

Use Mode ◀ / ▶ to walk through the seven modes of the current scale — the readout names where you are (“Mode 1 of 7 · Major (Ionian)”). It’s the fastest way to hear how Dorian differs from Aeolian, or why Lydian sounds bright: same notes, different starting point, played back so you can compare.

Harmonize it

The Harmony selector — off / 3rds / triads / tetrads / 6ths — stacks harmony on each scale tone (tetrads by default). Instead of a bare scale you hear the chords the scale generates, which is how you connect a scale to the progressions it implies.

The scale library

Don’t want to build from scratch? The scale library lists named scales — Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, and more — each labeled with its tetrachord construction, and a search box filters by name. Pick one and the toolkit loads its tetrachords so you can see how it’s built.

The keyboard below plays the scale tones on the on-device synth, with each key labeled for the current key.

What to Practice

• Build Major + Major in C, then swap the upper half to Upper Minor and hear it become Mixolydian.
• Set a major scale and step Mode ▶ through all seven — name each as you go.
• Turn Harmony to tetrads and play the scale to hear the seventh chords it produces.
• Search the library for “Lydian” and read its tetrachord construction.