Press start, then whistle! Your browser should ask for permission to use the microphone, and then you should start hearing a bass synthesizer that you control whith your whistle.
This depends a lot on latency. If you have a Mac running Firefox or Chrome, it should be pretty good, though in my testing Firefox is a bit better. This doesn't work in Safari yet because Apple hasn't implemented the AudioWorklet API.
Not currently recommended on mobile, because iPhone only supports Safari rendering and Android has unusably high audio latency.
Works best with headphones.
You can modify the settings by putting new numbers in the boxes and then moving to a new box. A good place to start is trying to change "octave" from "4" to "3". If you put in numbers that confuse it and it breaks, just refresh the page and start over.