Interval Based MIDI Keyboard

  • In Theory is an interval-based MIDI keyboard app. It has a keypad at the bottom which plays the notes in the scale you are working on.

    The keypad buttons are like +2, +1, 0, -1, +2 where;

    • - The 0 button plays the current note in the scale
    • - The +1 button plays the note after the current note in the scale
    • - The -1 button plays the note before the current note in the scale
    • - The +2 button plays two notes after the current note in the scale and so on.

In Theory has more than 110 scales that you can work on.

You can also use your custom scales that you created in ScaleBud 2!

Keypad of the app.

Create chord voices with intervals

  • You can toggle additional intervals in the scale for creating the chord voices.

    You can also add intervals from an octave below or an octave above, for creating rich extended chords.

    Chord intervals are not just the notes in the scale, they also include flattened and sharpened intervals as well.

    You can create as many patterns as you want from the bottom left of the app.

Chord intervals for richer sounds.

MIDI Controller Support

  • In Theory has MIDI controller and MIDI CC support.

    You can play In Theory with a MIDI Keyboard.

    • - The middle C4 key on your keyboard will trigger the 0 (root) button on the keypad
    • - The white keys after the C4 key on your MIDI keyboard will trigger the positive buttons on the keypad
    • - The white keys before the C4 key on your MIDI keyboard will trigger the negative buttons on the keypad

    You can toggle the chord intervals with MIDI CC. Assign a MIDI CC number and MIDI channel to chord intervals on the settings menu. You can send a MIDI CC value between 0-62 and toggle the intervals respectively.

    You can also sequence In Theory with a MIDI sequencer app such as PolyBud, ShiftBud or MelodyBud.

MIDI Keyboard support.

Take advantage of the AUv3 Plugin

  • In Theory app runs as standalone app as well as AUv3 MIDI Plugin.

    You can create AU presets and use AU parameters of the AUv3 plugin.

    You can control or even automate every AU parameter of In Theory.

    You can set the keypad range, octave range and MIDI CC and channel configurations in the settings menu.

Settings menu of the app.

Download for iOS or Apple Silicon

Open source

In Theory offers its core componets on Github.
They are all shared libraries for iOS, macOS and tvOS platforms, written in Swift.

Music Theory

A music theory library with Note, Interval, Scale and Chord representations in Swift enums.


Fully custumisable and editable knob with rotary, horizontal and/or vertical gesture recognition.


Free library for iOS.


MIDI Arpeggiator.


Generative MIDI Sequencer.

Other Apps

ArpBud 2

AUv3 MIDI Arpeggiator.

ChordBud 2

AUv3 MIDI Chord Sequencer.


AUv3 MIDI Recorder.


AUv3 Techno Bass Lines.


AUv3 MIDI Sequencer.


AUv3 MIDI Generative Sequencer.

ScaleBud 2

AUv3 MIDI Keyboard.


AUv3 MIDI Sequencer.


Multitrack Polyrhythmic Sequencer.


MIDI CC Sequencer.


AUv3 MIDI Sequencer.

In Theory

AUv3 MIDI Keyboard.


Bud App Controller.


Binary Based MIDI Sequencer.

Auto Bass

Bassline MIDI Generator.


Physics Based MIDI Sequencer.


Generative MIDI Sequencer.

Auto Fills

Drum Fill Generator.

Your feedback is important for us.