In Theory - Interval Keyboard 4+

Music theory based AUv3 MIDI

Cem Olcay

Designed for iPad

    • 5.0 • 3 Ratings
    • $4.99



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.

What’s New

Version 1.8

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+.

Ratings and Reviews

5.0 out of 5
3 Ratings

3 Ratings

App Privacy

The developer, Cem Olcay, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

Privacy practices may vary, for example, based on the features you use or your age. Learn More


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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StepBud - AUv3 MIDI Sequencer
ChordBud 2 AUv3 MIDI Sequencer
ArpBud 2 AUv3 MIDI Arpeggiator

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