After seeing various audio visualizers online in a variety of forms, I thought it would be a good idea to make one of my own and learn about the theory behind representing a waveform.
I had just built "Sin on a Circle" and so a circular style seemed sensible. The fundamental idea behind it doesn't change very much: at any given time, cycle through the of frequencies (here each bar is the average of a band of 3hz to make it a manageable number), get the relative amplitude of each frequency and increase the size of the given bar by that much.
It works with any .mp3 or .wav file, though I haven't added functionality for adding your own song. If you want to you can download the code from OpenProcessing or my GitHub and then add your own filepath.