Harmonize is an ear training app that helps you develop relative pitch and a feel for just intonation through hands-on listening.
It is useful not only for brass band and orchestra players, but also for singers who want more stable pitch, and for musicians who are comfortable with equal-tempered instruments such as guitar or piano but struggle with fretless instruments or vocal harmony.
Instead of learning pitch only as theory, Harmonize lets you train by listening to a target chord and adjusting your own pitch until the sound locks in. That practical, ear-first experience is the core of the app.
Recommended For
- People who want to improve their relative pitch
- Musicians who want to feel the sound of just intonation in practice
- Singers who want more stable pitch and harmony
- Players who want ear training that feels similar to tuning an instrument
- Anyone who wants to recognize pitch differences more intuitively
Why I Made This App
The idea for this app came from my own experience of starting the contrabass as an adult. Until then, most of the instruments I had played were fretted instruments such as electric bass and classical guitar. When I moved to a fretless string instrument, I quickly realized how exposed my pitch accuracy really was.
That led me to think about a better way to train the ear for pitch matching. Harmonize was born from that need.
Train Your Ear with Harmonize
In Harmonize, you train your ear by recreating the same chord as the reference chord.
First, the app plays the correct harmony. Then you adjust the pitch on the screen until the sound gets closer and closer. The experience feels very similar to tuning an instrument or trying to lock into a harmony by ear.
Erhu player Kobayashi-san also explains the gameplay clearly in the video above. In the current version, all intervals are based on just intonation.
What Is a Cent?
The app score uses a unit called a cent, which is a way to express very small pitch differences.
One octave is made of 12 semitones, but semitones alone are too coarse when you want to measure fine pitch errors. So each semitone is divided into 100 smaller units. That means 1 cent is 1/100 of a semitone.
In other words, 20 cents is one-fifth of a semitone, and 10 cents is one-tenth. Harmonize uses this value to show how close you were to the correct chord.
Just Intonation and Equal Temperament
Harmonize is based on just intonation.
Most modern instruments such as piano and guitar use equal temperament, which divides the octave into 12 equal parts. That makes modulation and key changes convenient.
By contrast, just intonation focuses on frequency ratios that produce cleaner harmonic relationships. For example, the interval from C to E is 400 cents in equal temperament, but slightly lower in just intonation.
$$ \mathrm{cents}_{\mathrm{JI}}=1200\log_2!\left(\frac{5}{4}\right) \approx386.314\ \mathrm{cents} $$
That means the just-intonation E is about 14 cents lower than the equal-tempered E. The number may look small, but the difference in harmonic clarity can be heard when the notes are played together.
If you want to hear that difference more clearly, the following video is helpful. The comparison between equal temperament and just intonation starts around 50 seconds.
With simple tones such as sine waves, the difference is very obvious. On richer instruments like piano or guitar, it can be harder to notice, but the cleaner resonance of a well-matched chord is still something your ear can learn to recognize.
There are even just-intonation guitars with unusual fret layouts, which show how different this approach can be in practice.
Final Thoughts
The key to matching just-intonation chords in Harmonize is to reduce the beating or “wolf tone” between the notes. As the wobbling sound gets smaller, the harmony becomes clearer and more transparent. That moment is the heart of the training experience.
What I like most about this app is that it lets you experience the difference not only as knowledge, but also through your own ears and hands. If you want to improve your sense of pitch, give it a try.
