Overview

Ongaku is a method for creating playlists programmatically, using only the content of the song alone. It uses gammatone cepstral analysis to create unique matrices to represent each song. A gammatone cepstrum is similar to the more common spectra used for audio analysis. Instead of doing a Fourier transform, we do a reverse Fourier transform, and then apply a transformation according to the gammatone function. This function was designed to mimic the signals sent to the brain through the cochlear nerve, the nerve which connects the ear to the brain.

The gammatone cepstra are then compiled together into a corpus, which is used for manifold learning (using sklearn). This creates a metric space for the songs in the library. The manifold learning process needs to be tuned to idealize the playlist outputs, but this is something which is difficult to define mathematically. I’ve had good results with n_components = 45 but your mileage may vary. I’ve defined a few rudimentary metrics which can be optimized over as well. We can draw shapes in this metric space, to define playlists.

The code will be documented in full at readthedocs.

The package is available on github.

Analysis

The analysis module is full of pre-processing methods to turn a song or song library into a gammatone cepstrum or gammatone corpus. It does also have tools for constructing a Fourier spectrum corpus, but the main usage is intended for gammatone cepstrum corpora. Corpora production has been parallelized in the preprocess function, but the default is to do this with a pool_size = 2 due to the fact that each gammatone analysis takes about 5GB of RAM to complete. In the event that I get around to building a gammatone function that isn’t a MATLAB port, this may change, but for now, only increase pool_size if you know your machine can handle it. preprocess, as the main workhorse, will put a corpus.pkl in your working directory, which will be needed for the learning and construction stages.

Learning

The learning module implements a couple of manifold learning techniques, and is fully compatible with sklearn, so it should interact well with any other pipelines. The gammatone cepstra can be compiled into a corpus, and then used for manifold learning using the cropped_corpus function, and then the flatten_corpus function, whose output is safe to use for generalized sklearn operations. The learning module also contains the generate_m3u function, which takes a list of tags and generates a .m3u file which represents the location of the specified songs on your computer, being a playlist which is compatible with all major music players.

Metrics

The metrics module contains a number of naïve metrics to measure the “compactness” and the “disjointness” of the resultant manifold. They, while useful to compare different manifold generation methods to each other, don’t give a great idea as to how to tune metaparameters, since they’re really just measures of the degree to which the curse of dimensionality is affecting your data.

Playlists

The playlists module contains some algorithms for generating playlists from input songs and the manifold data frame. They mostly involve drawing geometric shapes on the manifold and sorting the songs within those n-volumes by distance from some object. For example, the distance playlist draws an n-circle around the input song, with radius equal to the distance between the input song and the m-th closest song.