Lesson 11 · All 12 keys

Diminished Chord Triad Trainer

Learn how a diminished triad is built one semitone-count at a time, then put it to work with two MIDI exercises: playing all 12 diminished chords around the circle of fourths, and a pleasant four-chord progression — containing just one diminished chord — in every key.

How a diminished triad is built

A triad is a 3-note chord. Every diminished triad — in any of the 12 keys — is built the exact same way, by counting semitones to the right from a root note:

  1. Start on the root — the note that names the chord.
  2. Count 3 semitones to the right to land on the minor 3rd.
  3. From there, count 3 more semitones to the right (6 semitones from the root) to land on the diminished 5th.
Example — C diminished: start on C, count 3 semitones right to reach E♭, then count 3 more semitones right to reach G♭. C‑E♭‑G♭ is the C diminished triad. The pattern 3 then 3 (6 semitones total from root to top) is what makes a triad "diminished" — every one of the 12 diminished chords is this same shape, just moved to start on a different key.
Compare this to a minor triad, which counts 3 then 4 semitones instead — the diminished triad simply lowers that perfect 5th by one more semitone, turning it into a diminished 5th (also known as a "tritone", exactly 6 semitones — half an octave). Because that 6-semitone gap splits the octave right down the middle, it has no perfect 5th to lean on and no stable "home" feeling, which is exactly what gives the diminished triad its tense, restless sound. That tension is also what makes it so useful musically — it wants to resolve, which is exactly why it works so well as a passing or leading-tone chord between two others rather than as a destination in itself.

Try it: pick a root and build the chord step by step

Step 1 of 3
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Chord toneNoteSemitones from rootMIDI #

All 12 diminished triads at a glance

ChordRoot+3 semitones → 3rd+3 semitones → dim 5th

This MIDI exercise plays all 12 diminished chords, one after another, moving around the circle of fourths — each chord's root sits a perfect 4th (5 semitones) above the last one: C → F → B♭ → E♭ → A♭ → D♭ → G♭/F♯ → B → E → A → D → G → back to C. Every chord is played as a full triad (root, 3rd, and diminished 5th together).

Chord 1 of 12
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The 12 chords, in circle-of-fourths order

#ChordRoot3rdDim 5th

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Key of C
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Progression in C

DegreeChordRoot3rd5th