This was my final project for my Sensors & Transducers class at UGA. It's a simple python script that takes a .WAV file of a chord as an input and outputs the notes that are in the chord. The horrible title is a portmanteau of "chord" and "oracle".
It works by performing a Fourier transform and then computing the "Harmonic Product Spectrum", i.e. taking the geometric means of the magnitudes of the Fourier spectrum for a base note and a set of its low harmonics - right now, we consider 5 harmonics (this seems to be about the sweet spot) across the standard pitches from E2 to E4 (this is just a demonstration, and should be expanded to include the full range of notes that one would expect to be present in a chord). The program simply outputs the notes corresponding to the 5 greatest harmonic products.
The Harmonic Product Spectrum is cool - it's a simple concept (with surprisingly little academic research) that extends the Fourier transform's frequency domain representation, where instead of representing the strength of an individual frequency or a single sine wave, we have a quantity that represents the presence of a true musical note - including its harmonics, and invariant of its timbre.
Included is gmaj.wav, a G Major I recorded on my guitar. For example, run:
python run.py gmaj.wav