I also wanted to nitpick this part of the article -- the neural network isn't determining the audio features; these are all hand-engineered features developed b

I also wanted to nitpick this part of the article -- the neural network isn't determining the audio features; these are all hand-engineered features developed by The Echo Nest. The neural network is trained to mimic collaborative filtering vectors from raw audio. It's a separate model from time signature, key, mode, tempo, loudness, etc.