# In Theory - Interval Keyboard — Music theory based AUv3 MIDI

> Interval-based MIDI keyboard app with over 110 scales for music creation. (iPhone/iPad app by Cem Olcay.)

- Source: https://appshunter.io/ios/app/in-theory-interval-keyboard/id1667984658 (this page in markdown: same URL + `.md`)
- Developer: [Cem Olcay](https://appshunter.io/developer/523633853)
- Category: Music, Utilities
- Price: $4.99
- Rating: 5.00/5 from 4 App Store ratings · 2 written reviews indexed
- Age rating: 4+
- Requires: iOS 12.0 · 23 MB
- Languages: American English
- Released: 2023-02-21
- Data updated: 2026-08-23
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/in-theory-interval-keyboard/id1667984658/reviews.md

## What is In Theory?

In Theory is an interval based MIDI keyboard app with more than 110 scales. It has a keypad at the bottom with the interval buttons like +2, +1, 0, -1, -2 which would change the current note. Zero means the current note, +1 means the note after the current note, +2 means two notes after the current note, -2 means two notes before the current note in the scale and so on. 

Above the keypad, you can toggle additional intervals in the scale for creating chord voices. You can also select the notes from an octave above and an octave below for creating rich, extended chords. 

You can use your MIDI keyboard to play In Theory as well. The middle C4 key on your MIDI keyboard triggers the 0 (zero) button on the app's keypad. The white notes after the C4 note would trigger the positive buttons, the white notes before the C4 note would trigger the negative notes on the keypad. 

You can also toggle the chord intervals with MIDI CC messages. You can set a MIDI CC number and a MIDI Channel for toggling the chord intervals from the settings menu. If you send a MIDI CC value between 0-62, you can toggle the chord intervals respectively. 

With the MIDI capabilities, you can also sequence the app with a MIDI sequencer app like PolyBud, ShiftBud, MelodyBud etc. 

In Theory has more than 110 scales built-in. You can also use the custom scales you made in ScaleBud 2 app as well. The key and scale could be changed externally from a MIDI controller in AUv3 plugin with the AU parameters. 

The circular display on the UI will show you where you are in the scale. Also, when you play a note, you will see the every playing note on the screen with the root note and the chord intervals. 

Please note that In Theory is a MIDI app and does not produce any kind of sound on its own. You need to connect the MIDI output of the app to an audio app's MIDI input. For the AUv3 plugin you'll need an AUv3 host app such as AUM, Cubase, Nanostudio, apeMatrix etc.

## Key features

- Interval-based MIDI keyboard
- Over 110 built-in scales
- Customizable chord voicing
- MIDI keyboard input support
- MIDI CC message control
- AUv3 plugin compatibility
- Visual scale and note display

## Recent user reviews (2 of 2)

All indexed reviews: https://appshunter.io/ios/app/in-theory-interval-keyboard/id1667984658/reviews.md

### 5/5 — Another winner

*2025-08-02*

Cems apps are never boring and this is no exception. An interesting and useful app!

### 5/5 — Dope

*2023-12-14*

Love it

## Frequently asked questions about In Theory

### What is In Theory?

In Theory is a MIDI app that functions as an interval-based keyboard. It offers over 110 scales and allows users to create complex chords by adjusting intervals and octaves. It does not produce sound on its own and requires connection to an audio app.

### Does In Theory have ads?

No, In Theory is ad-free. As a paid application, it provides an uninterrupted user experience without advertisements.

### What devices does In Theory support?

In Theory is available for iPhone, iPad, and iPod. It is designed to work across these Apple mobile devices.

### How does In Theory handle scales?

In Theory comes with over 110 built-in scales and can also utilize custom scales created in the ScaleBud 2 app. The selected key and scale can be changed externally via MIDI controller in AUv3 plugin.

### Can I use my physical MIDI keyboard with In Theory?

Yes, you can use your MIDI keyboard to play In Theory. The middle C4 key on your MIDI keyboard triggers the '0' button on the app's keypad, with other keys triggering positive or negative interval buttons.

### What is the price of In Theory?

In Theory is a paid application priced at $4.99. This one-time purchase grants full access to all its features.

### How often is In Theory updated?

The latest version of In Theory is 2.2, last updated on September 27, 2024. This indicates a relatively active development cycle for the app.

### What is the age rating for In Theory?

In Theory has an age rating of 4+. This suggests it is suitable for a wide range of users, including younger individuals interested in music.

## Version history (last 5 releases)

### 2.2 — 2024-09-27

This version adds an internal polyphonic sampler with piano sound to the standalone app.

### 2.1 — 2024-09-02

This version updates the support section on the settings menu.

### 2.0 — 2024-07-18

This version updates key and scale picker. 
- The scale picker won't close when you pick a scale. 
- You can select and audition a scale when you select one. 
- The scale picker will close when you press the done button on the top right. 
- You can select and audition a key and an accidental.
- The key picker will close when you press the done button on the top right.

### 1.9 — 2024-06-29

This version updates the bottom toolbar UI. 
- Adds min and max octave knob controls. 
- Adds root button for returning to the root note at the middle octave quickly. 
- Performance updates and minor fixes.

### 1.8 — 2024-04-22

This version updates the scale picker. 
- Adds new favorite section and lets you mark the favorite scales. 
- The favorite scales will be universal between the Bud apps.
- Scale picker shows the current scale with a checkmark.
- Fixes the scale picker search bar's case sensitive search.
- Fixes the "rate app" link on the settings menu for iOS 17+.

## Apps similar to In Theory

| App | Rating | Price | Category |
| --- | --- | --- | --- |
| [Piano Chords and Scales](https://appshunter.io/ios/app/piano-chords-and-scales/id714086944) | 4.8 (9,159) | Free | Music |
| [TONALY: Songs, Scales & Theory](https://appshunter.io/ios/app/tonaly-songs-scales-and-theory/id1242467844) | 4.8 (6,314) | Free | Music |
| [Piano Chords, Scales Companion](https://appshunter.io/ios/app/piano-chords-scales-companion/id598574333) | 4.8 (1,315) | Free | Music |
| [Circle o Fifths: Guitar+Piano](https://appshunter.io/ios/app/circle-o-fifths-guitar-plus-piano/id1499417636) | 4.8 (1,045) | $2.99 | Music |
| [Note Quest: Learn Piano Music](https://appshunter.io/ios/app/note-quest-learn-piano-music/id1176943393) | 4.5 (609) | Free | Music |
| [Tonality: Music Theory](https://appshunter.io/ios/app/tonality-music-theory/id1467552236) | 4.8 (128) | $7.99 | Music |

## More apps by Cem Olcay

- [FretBud - Chord & Scales AUv3](https://appshunter.io/ios/app/fretbud-chord-and-scales-auv3/id1234224249)
- [ScaleBud - AUv3 MIDI Keyboard](https://appshunter.io/ios/app/scalebud-auv3-midi-keyboard/id1409125865)
- [StepBud - AUv3 MIDI Sequencer](https://appshunter.io/ios/app/stepbud-auv3-midi-sequencer/id1453104408)
- [RhythmBud - AUv3 MIDI FX](https://appshunter.io/ios/app/rhythmbud-auv3-midi-fx/id1484320891)
- [ArpBud 2 AUv3 MIDI Arpeggiator](https://appshunter.io/ios/app/arpbud-2-auv3-midi-arpeggiator/id1500403326)
- [ChordBud 2 AUv3 MIDI Sequencer](https://appshunter.io/ios/app/chordbud-2-auv3-midi-sequencer/id1526221230)

All apps by Cem Olcay: https://appshunter.io/developer/523633853

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-23.*