Press the space bar to show the options. This visualizer only reads audio that comes through your computer's microphone, so you need to allow scratch the ability to record audio. The blue box in the top right corner is the loudness that the program senses. Press 0 through 9 to view some scratch songs to play and test. Enjoy!
It's simple, but I'm trying my best. I did everything myself, except for the music that scratch has provided. You can use your own music on this program as well, just make sure your device can hear the music.
