Play in Any Key

Compare chord progressions across all 24 major and minor keys—even those you find hard to play. Find your favorite progression and key combination.

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Inspiration

I studied the Electone (electronic organ) for 13 years and still enjoy playing it as a hobby. I love melodies, of course, but I especially love the sound of chords and bass — I enjoy chord progressions so much that I could listen to them on their own for hours.

With easier keys, I can play a progression myself and quickly hear how it sounds. But with more difficult keys, that is not always easy.

That made me wish for an app where I could play a chord progression with one tap and easily switch between different keys to compare how they sound. That idea became Play in Any Key.

What it does

Play in Any Key is an app that lets anyone intuitively explore and enjoy their favorite chord progressions and sounds, even without knowledge of music theory or the ability to play an instrument.

Users can choose a key from a piano-style keyboard and listen to around 80 chord progressions to discover the sounds they like. The app supports all 24 major and minor keys, making it easy to switch keys and compare how the same progression sounds in each one.

If users find a progression they like, they can simply listen to and enjoy it. If they want to explore further, they can combine different chord progressions or change individual chords to create their own progressions.

From there, they can take it one step further by combining their favorite progressions into verse, pre-chorus, and chorus sections to create and enjoy a complete song structure.

Users can also add bass, rhythm, and drums to explore how different arrangements change the feel of a chord progression.

From “listening” to “discovering,” “connecting,” and finally “turning it into a song,” Play in Any Key is designed to let people experience music in their own way, without being limited by musical knowledge or performance skills.

C major is available for free.

A one-time in-app purchase unlocks the other major keys and all minor keys.

How I built it

I built Play in Any Key for iOS using SwiftUI.

The app can play chord progressions across all 24 major and minor keys, using chord inversions to keep the movement between chords smooth and natural.

I also implemented bass, rhythm, and drum playback, and used RevenueCat to manage the in-app purchase.

Challenges we ran into

One of the biggest challenges was making sure the chord progressions sounded natural in every key.

I repeatedly listened to the progressions myself, checked for anything that sounded unnatural, and adjusted the chord inversions and movement between notes until the transitions felt smooth.

Creating the rhythm and drum patterns was also challenging. I referred to books I used when I was learning the Electone and experimented with combinations of kick, snare, hi-hat, and other sounds, listening and adjusting them by ear until they worked well with the chord progressions.

Accomplishments that we're proud of

What I am most proud of is creating chord progressions that flow naturally without awkward transitions, making them enjoyable and satisfying to listen to on their own.

I also made it possible to play progressions in keys that may be difficult to perform yourself and easily compare them across all 24 keys with just a few taps.

What we learned

While developing the app, I discovered the wide variety of instrument sounds, drum samples, and other audio resources available for music production.

I learned how to combine these sounds and repeatedly listen and adjust them to create rhythm and drum patterns that fit naturally with the chord progressions.

I also learned how much the overall sound can change depending on how individual sounds are combined and played.

What's next for Play in Any Key

Next, I would like to add more rhythm and drum patterns, as well as more chord progressions, so users can enjoy an even wider variety of sounds and musical styles.

I also want to further develop the flow from “listening” and “discovering” to “connecting” and “turning it into a song,” adding more ways for users to expand a sound they love into their own music.

My goal is to continue developing Play in Any Key into an app where anyone can enjoy making and exploring music starting from a sound they love, regardless of their knowledge of music theory or experience playing an instrument.

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