Case studies / Sound Theory, music theory you can play
Sound Theory, 2026
Sound Theory, music theory you can play
Music theory is usually learned from books and videos: listening, not doing. I learn by doing, and I wanted to play with harmony the way Jacob Collier talks about it, steering a chord to make you feel something. Sound Theory listens as you play, names the chord, and suggests where it could go next by feeling, so you pick up a little theory while you experiment.
soundtheoryapp.com↗- Client
- Self-initiated
- My role
- Founder, designer and developer
- Who it's for
- People who want to play and experiment with music, and learn a bit of theory by doing it
- Built with
- Claude Code, Expo and React Native, Web MIDI and Web Audio, a shared music engine
- Status
- Live on the web since 27 October 2026, and coming to the App Store for iPad and iPhone
- Duration
- 2026
- Outputs
- Web app, iPad and iPhone app, Chord Compass, Play together, 23 songs to play along to, a design system
Results
The results
What the work produced.
- Six ways on from any chord you play In your key, Resolve, Tension, Brighter, Darker and Far away, each shown on the keys with the notes that stay and the notes that move.
- Chords suggested by feeling, in colour Every key has its own colour round the circle of fifths, and each idea says how it will feel before you play it.
- A friend's request live in about 30 minutes Friends played it while I built it. They asked for guitar and for it to hear chords through the mic, and both are in.
- Play together, anywhere Jam with friends, or put on a small performance for people anywhere on the internet.
- Any keyboard, or none at all Plug in a keyboard, or play piano or guitar near the microphone and it listens.
Learning by doing, not by being lectured
Music theory is taught through books and videos: listening, not doing. Some of us learn by doing, with a different part of the brain, and my A4 chord charts could not show how the chord under my hands connected to the theory.
So the rule from the start: the theory answers the chord you are playing, as you play it. It is for people who want to play and experiment, and pick up a bit of theory with a practical, visual use while they do.
From heady theory to feeling the music again
I love how Jacob Collier talks about harmony: changing a chord to make the listener feel something different. He understands the theory underneath so well that he can steer the tone and feel at any moment, instead of hunting around at random.
I wanted people without his depth of theory to explore music his way, but visually and by playing. Chord Compass offers six directions from any chord, In your key, Resolve, Tension, Brighter, Darker and Far away, shown on the keys as you play.
A circle of fifths you can feel
The circle of fifths usually lives in a theory book as a black and white diagram. It is the part of the app I love most, and the part my friends loved first.
Every key has its own colour, and the six ideas sit round the circle in their key's colour. Sharps come in and the sun comes out; flats come in and it goes in. You can see where a chord will take you, and how it will feel.
Pages that fit while your hands are busy
The first app build had panels scrolling inside panels and controls cut off. With both hands on the keys, a player cannot stop to hunt for the next step.
Before fixing another screen I set a design system, with two kinds of page: one that fits the screen and one that scrolls as a whole. A lesson now fits one screen and hears each chord you play.
Shaped by friends playing it
Two friends played it while I built it. They loved the colours and Your journey, which keeps the chords you play so you can play them back or turn them upside down.
They asked for guitar, for it to hear chords through the mic without a keyboard, and for Your journey to follow them round the app so they could keep fiddling with a progression. Guitar and the mic are in now.
Real music to play along to
Songs are another way to practise: the same chords, inside music you know.
There are 23 pieces, from Ode to Joy to a Chopin nocturne, each in an easy version and one close to the original. The score scrolls, the keys light with each note, and the chord under your hands is named as you go.
Music is more fun with other people
Music is more fun with other people, whether they are friends or someone you have never met.
Send a link to a friend, or list your session so anyone can join. Up to eight people play at once, each in their own colour, with the chord name following everyone's notes. Jam with friends, or put on a small performance for people anywhere on the internet.
Reflection
What I did not expect
The moment it worked for me was a chord sequence I have played for years and never known how to take further. I wanted it darker, then tension, then resolve, and until then my only method was trying random notes. The app showed me the way, and taught me the theory behind it as I played.
Friends played it as it grew. One would ask for a feature and it would be live about 30 minutes later, so the people using it shaped it while it was being built. It opens up a different model of product development: testing the real thing with the people using it, and changing it in hours.
Next, I hope a community grows around it: songwriters and hobbyists playing with music while they learn and discover.
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