In Theory - Interval Keyboard3.3 - App Store

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.

Version History This version updates the AUv3 state saving. 3.3 Sep 24 This version improves the app stability. 3.2 Sep 22 This version fixes the tutorial link in the AUv3 settings menu. 3.1 Sep 18 This version fixes the crash issue on the AUv3 MIDI plugin, when the plugin runs in the background for a long while. 3.0 Sep 12 This version adds an internal polyphonic sampler with piano sound to the standalone app. 2.2 09/27/2024 This version updates the support section on the settings menu. 2.1 09/02/2024 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. 2.0 07/18/2024 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. 1.9 06/29/2024 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+. 1.8 04/22/2024 This version adds support for running the app on Apple Silicon Macs. 1.7 05/29/2023 This version adds support for saving AU presets in the AUv3 plugin.
The saved preset will be shared between multiple AU hosts. 1.6 04/19/2023 This version adds "Return to Root" and "Return to Mid Root" AU params to the AUv3 plugin.
You return to the current key in the current octave or mid octave with those parameters. 1.5 04/13/2023 This version adds "return to root key" feature. 
If you send C# note to In Theory, it sets the current note the root note in the middle octave.
If you send D# note to In Theory, it sets the current note the root note in the current octave.
You can use this feature either with external MIDI controllers or MIDI sequencers. 1.4 04/11/2023 This version adds BrainBud app compatibility. 1.3 03/06/2023 This version fixes the MIDI hanging note issue when you drag your finger around 0(zero) key on the keypad. 1.2.1 02/26/2023 This version makes the circular key are touchable. You can play notes by pressing the circle keys as well.
Also fixes MIDI hanging note issue. 1.2 02/24/2023 Minor fixes on the standalone app. 1.1 02/22/2023 1.0 02/21/2023