Copyright Shawn T. O'Neil, 2013 | p5.js port 2025 | Licensed under CC BY-NC 4.0
Interval is an interactive tool for exploring music theory. It visualizes notes, scales, and chords on a circular display, and lets you hear how different tuning systems affect the sound of music.
There are two ways to play notes:
You can also click notes on the wheel. When you play multiple notes together, the app identifies the chord (a group of notes that sound good together) and displays its name in the center. Common chords include major (happy/bright), minor (sad/dark), and seventh chords (jazzy/complex).
The wheel shows all 12 notes arranged in a circle. Bright notes are "in the scale" - they belong to your selected key and will sound harmonious together. Dimmed notes are "outside the scale" - they can add tension or color but may clash.
Circle of Fifths: This toggle changes how notes are arranged. Normally notes go up by half-steps (C, C#, D, D#...). The Circle of Fifths arranges them by "fifths" instead (C, G, D, A...). A fifth is the interval from "do" to "sol" - one of the most consonant sounds in music. This arrangement reveals why certain chords sound good together: neighbors on the circle share many notes.
Chromatic Colors: Changes whether colors represent pitch (low=red to high=violet) or position in the circle of fifths.
The small dot shows the relative major/minor. Every major key has a "relative minor" that shares all the same notes but starts on a different root. For example, C Major and A Minor use the same seven notes (all white keys on a piano).
A scale is a collection of notes that sound good together. The most common are:
Modes are variations of a "parent" major scale, each starting on a different note. Modes of the same parent scale share all the same notes but have different "home bases," creating distinct moods:
The app shows which "parent" major key shares the same notes. For instance, D Dorian uses the same notes as C Major - it's just "C Major starting on D."
A chord progression is a sequence of chords. Most songs use the same few progressions. The numbers (1, 4, 5, etc.) refer to scale degrees - if you're in C Major, 1=C, 4=F, 5=G.
Progressions are mode-aware: the same "1-4-5" pattern produces major chords in a major key but minor chords in a minor key. Try switching between C Major and C Minor while a progression plays to hear the difference.
Here's a secret: the notes on a piano are slightly "out of tune" - on purpose! A temperament is a system for tuning notes. The challenge is mathematical: you can't have perfectly pure fifths (3:2 frequency ratio) AND perfectly pure thirds (5:4 frequency ratio) AND be able to play in any key. Different temperaments make different trade-offs.
Important: Except for Equal Tempered, all temperaments are "keyed" - they're designed around a specific root note. The samples in this app are tuned relative to C, so C Major represents the "home" key where the tuning is optimized. When you select a different root note, the temperament characteristics shift accordingly - you're essentially playing in a key that's "farther" or "closer" to the tuning's home base.
Equal Tempered (Modern Standard)
The one temperament that isn't keyed. Every half-step is exactly the same size, so every key sounds identical and you can transpose freely. The trade-off: no interval is perfectly pure (e.g. a perfect fifth should be 3:2 = 1.5, but in equal temperament it's ~1.498). This tiny compromise in every interval is why modern instruments can play in any key. This is how virtually all contemporary instruments are tuned. Listen to C Major then F# Major - they sound identical in character.
Well Tempered (Baroque Era)
Notes are adjusted so that all keys are playable, but each key retains its own "color." Keys close to C (few sharps/flats) sound purer and brighter because the tuning favors them. Keys far from C (like F# Major with six sharps) accumulate small tuning compromises that make them sound more tense and darker. Bach wrote "The Well-Tempered Clavier" specifically to showcase how each of the 24 keys has its own character. Compare C Major (pure) to F# Major (edgy) - you'll hear C sound clean while F# has more tension.
Pythagorean (Ancient Greek)
Built entirely by stacking pure fifths (3:2 ratio) starting from C. Fifths sound incredibly pure, but here's the problem: if you stack 12 perfect fifths (C→G→D→A→E→B→F#→C#→G#→D#→A#→F→C), you should return to C - but mathematically, you land slightly sharp. This leftover error (called the "Pythagorean comma") has to go somewhere, creating one horribly out-of-tune interval called the "wolf fifth" - traditionally placed between G# and Eb where it was least likely to be needed. Hear the wolf fifth - instead of a pure fifth, you get a dissonant howl! Compare to a pure C-G fifth.
Carlos Super Just
Created by electronic music pioneer Wendy Carlos for her groundbreaking synthesizer albums. This is a form of "just intonation" - tuning based on pure mathematical ratios. Chords in C and nearby keys sound incredibly pure and beatless because their intervals are exact ratios (like 5:4 for major thirds). But this purity comes at a cost: keys far from C sound noticeably out of tune. Compare C Major (pure, locked-in) to F# Major (buzzy, restless) to hear the dramatic difference.
Toggle Spectrum to see a visualization around the wheel that responds to the sounds being played. It combines frequency analysis with direct note tracking for a fun (if not scientifically precise) display.
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Explore music theory through an interactive visualization. Play notes, build chords, and discover how different tuning systems change the sound of music.
Make chords - press multiple keys together:
You can also click notes on the wheel. Press ? for full help.