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Auto Chord

Auto Chord is a "chord follower" that automatically generates chord accompaniment from live music. Unlike apps that require the user to manually program a sequence of chords, Auto Chord automatically detects chord notes and uses the information to control a pad synth, which is included within the app.

The chord detector uses a model based approach to pick the best chord based on harmonic similarity and complexity (see paper on ResearchGate) User controls include trigger level set sliders (note on/off levels), and a list of the types of chord to use (e.g., major, minor, 7th, diminished, etc.).

The internal pad synth is based on our xMod FM synthesis technology. A touch sensitive sound space controls timbre of the instrument. Other controls change register, decay, and portamento.

N.B. Although the app works with most music, it is essential the music be "in tune" (A4 = 440 Hz). It is also best to minimize percussion and ambient noise.

How to Use

Adjusting the bottom two sliders change trigger (note on/note off) levels. A row of lights above the keyboard shows the instantaneous output of the pitch detector bank collapsed into a single octave (chromagram). Tap the gear icon to access the settings table, which lets you specify what chords to use. Thirteen types of chord are defined:

  • Single note (no chord)
  • 5th (no 3rd)
  • Major
  • Minor
  • Diminished
  • Augmented
  • Dominant 7th
  • Minor 7th
  • Major 7th
  • Sustained 4th
  • Diminished 7th
  • Minor 7th with flat 5th
  • Minor with #7th
Only those chord types that are selected are matched against the music being played. Tap the gear to dismiss the settings.

Tap "Synth" to access the built in FM synth. Feedback will occur if the sound output from the synth is picked up by the device's microphone. The top slider blends the input audio (left) with the output of the synthesizer (right). Tap the bottom left button to change the register (+/- 2 octaves). The decay control allows you to extend the normal decay of the synth. Portamento adds some interesting "sci-fi" like effects.

The following demo video shows Auto Chord operating by itself (with headphones) and within the Audiobus 3 environment.

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