The Octave Lab
Harmonize any scale, up and down, in all 24 keys, on keyboard and guitar. Four centuries of answers to one question, from the Baroque masters to Barry Harris and gospel.
Free. Runs in your browser. No sign-up.
One question
What chord goes on each note of the scale, going up and coming down?
Every player hits this wall. You know your chords. You know your scales. But put a bass line under your fingers and the harmony falls apart, because nobody showed you how the two fit together.
In the 1700s, keyboard students learned the answer right after their first cadences. They called it the Rule of the Octave: a chord for every step of the scale, memorized in every key until it lived in the hands. It is the reason a church organist could improvise for an hour and a harpsichordist could accompany anything at sight.
Then it disappeared from most lessons. The Octave Lab brings it back, and shows how the same idea runs straight through Liszt, bebop, jazz piano and gospel.
What's inside
Thirteen ways to harmonize the same scale, three centuries apart.
- Thirteen ways to harmonize the same scale, side by side. Pick a key and hear the classical Rule of the Octave next to Liszt, Dupré, C.P.E. Bach, Barry Harris, secondary dominants, tritone subs and an R&B walk-up. Listen for where they part ways.
- All 24 keys, one click. Every exercise transposes to any major or minor key, spelled correctly.
- Plain, expanded or modern. Play the original chords, or switch to lush voicings: 6/9 tonics, 9th and 13th dominants, 7alt in minor, maj13 on the subdominant.
- See both hands. A keyboard shows the left and right hand for every chord, with the chord tones colour-coded.
- Guitar that actually fits the hand. Three ways to play each chord: smooth shapes, Kirkman's classical positions with fingerings, or partimento voicings that follow the keyboard's top line.
- Barry Harris drop-2, the real way. The sixth-diminished scale in true drop-2 shapes on one string set, climbing the neck.
- Hear it, then play it. Block chords, a rolled prelude texture, or suspensions in the top voice.
- Take it into your DAW. Export MIDI for any line, key or the whole collection, with separate tracks for each hand and the guitar.
- Dandrieu's 23 tables included. The full set of exercises from Jean-François Dandrieu's 1718 method, every bass pattern named, playable in the original or expanded.
Who it's for
- Keyboard players who can read chords but freeze when the bass moves. Learn what to play over any step of the scale, in any key, without thinking.
- Guitarists who want real harmony, not just shapes. See the same progression as fretboard fingerings, positions and voice leading.
- Producers and songwriters who want chord movement that sounds intentional. Pull a walk-up, a lament bass or a gospel passing chord straight into your session as MIDI.
- Jazz and gospel players who want to know where their vocabulary comes from. Hear how a Baroque suspension becomes an R&B polychord.
- Teachers who need one exercise that works for every student, every key and every instrument.
Four centuries, one question
The answer kept changing. The question never did. The Octave Lab lets you hear every generation's answer in the same key, one after another.
| When | Who | What they added |
|---|---|---|
| c. 1718 | Jean-François Dandrieu | 23 tables of bass patterns, the Rule of the Octave in practice |
| 1700s | C.P.E. Bach and the Naples schools | Suspensions, chromatic scales, the octave as a launchpad for improvising |
| c. 1842 | Joseph Kirkman | The Rule of the Octave fingered for guitar, position by position |
| Late 1800s | Franz Liszt | Scales in Chords: the octave as piano technique, through all 24 keys |
| 1920s | Marcel Dupré | The scale moved into the soprano and the tenor, against a moving bass |
| From the 1970s | Barry Harris | The sixth-diminished scale: tonic and dominant alternating on every step |
| Today | Jazz, R&B and gospel players | Shell voicings, tritone subs, passing chords, polychords |
Same scale. Same bass. Three hundred years of better answers.
Ten minutes a day
The old masters practised a little of it every day. Here's how to do the same.
Listen first.
Open Compare the Octaves in C major. Play two harmonizations back to back and name one place they differ.
Play it plain.
Take one line in Basic harmony. Play it up and down with the root, then the 3rd, then the 5th on top.
Change keys.
Move it to a new key every day. By the end of a month you've covered all 24.
Add colour.
Switch to Expanded harmony and play the same line with modern voicings.
Make music.
Turn on the arpeggio or suspension texture, slow it down, and improvise a short prelude over it. Export the MIDI and build a track on it if you produce.
FAQ
Learn the octave once. Use it for life.
The masters drilled it until it lived in their hands. Start with one key today.