No Echo Nest code was included in this project specifically, but my team owns a lot of the old Echo Nest systems, data, and audio magic (i.e.: what used to be the Remix API, audio features, audio analysis, etc.). Pedalboard is being used to continue a lot of the audio intelligence research that started way back with the Echo Nest!
(Fun fact: the Echo Nest's Remix API was what got me interested in writing code way back in high school. Now, more than a decade later, I'm the tech lead for the team that owns what's left of it. I still can't believe that sometimes.)
I've done a lot of stuff with the Audio Analysis API, and it's horribly underdocumented. I tracked down the phd thesis that formed the basis of that array some time ago[0], but it's pretty theoretical and likely outdated. Do you think you'll ever get around to actually documenting that API?
(Fun fact: the Echo Nest's Remix API was what got me interested in writing code way back in high school. Now, more than a decade later, I'm the tech lead for the team that owns what's left of it. I still can't believe that sometimes.)