A fun new online interactive musical experience between humans and computer gives us a good example of machine learning. The experimental gadget is called A.I. Duet and it calls Tone.js which allows you to play a question-answer game with the computer on a MIDI keyboard. The machine listens to you play, then replies to you. In terms of programming, what makes this example interesting is that the algorithm knows nothing of musical theory, nothing of musical notation or rhythm, at least nothing in the form of rules as we would imagine. Its reference is some musical examples which the programmer has given it as models to build its neural networks.