A music sheet writer !
Alba is a python project that can write a complete score of a given .WAV file ! I managed to get a mere 60% of accuracy. The score is given using the Lilypond format. You can then export them into .pdf using Lilypond.
For the first version, Alba uses Fourier decomposition to analyze the spectrum of the audio file and associates frequencies to notes, giving a prototype of what the score looks like !
I also managed to use an unsupervised machine learning algorithm, Non-Negative Matrix Factorization, which iteratively decompose a given matrix (here the spectrogram of the recording) into a matrix of base vectors and a matrix of coefficients, or "activations".