It might not be inline with your exact goals, but I've really been enjoying doing audio visualization lately.

I'm using the Unity game engine, and am leaning heavily on already-implemented FFT algorithms available on the Unity AudioSource component, but the fun part is taking the spectrum data, dividing it up into bands, and doing visuals with those.

Here is a short video showing a simple audio visualization demo I created: https://www.youtube.com/watch?v=kYt0dcUY3i8

It led me down a bit of a rabbit hole with watching videos about Fast Fourier Transforms, and learning more about audio specific programming.