The knob is not an invention that changes the world, but it can do things that the keys can't do.
As a mechanical construction, we don’t know which device used the knob first. Maybe a telegraph machine in the last century? Or a oscilloscope? It may also be a radio or a TV later, which is naturally born on electronic devices like many buttons, and then gradually became popular as a part of the audio equipment, and has been used as a controller ever since.