Achord is a Max for Live application which is able to detect tonal information live, directly from an incoming audio signal. Surprisingly, although the supporting research is nearly 20 years old, this sort of application is not currently offered by anyone else within the Max for Live community.
The application uses functions run inside the Node for Max runtime environment to perform spectral processing on the incoming signal. To be specific, we are performing a Short-Time Fourier Transform (STFT) on overlapping windows of the signal. The resulting spectogram is further processed to extract a Harmonic Pitch Class Profile (Gomez et al., 2006), which is defined as a vector of relative intensities of each of the 12 pitch classes of the equal-tempered scale within an analysis frame. This vector can then be compared to pre-defined templates to determine the corresponding chord label.
To use inside Ableton, download the exported Max for Live patch from https://maxforlive.com/library/device/6063/achord - then simply drag-and-drop achord.amxd into the Ableton device area.
The device should be active when you load it - this is indicated by the red light. In theory that's it but if if you want to save CPU you can stop or deactivate the plugin. If you've stopped the plugin, you can use restart to activate it again.
There are three chord modes you can choose from:
majmindetects only major and minor chordsmajmin7which in addition to major and minor, detects major7 and minor7 chordsalldetects major, minor, major7, minor7, dominant, augment, and major minor chords
To run tests: npm install && npm test
Mocha is used for testing