If the Arduino board can listen and feel with sensors, it can also react by making things move.
By the movement concept, I mean both of the following:
Object movements
Air movements producing sounds
We are going to learn how we can control small motors named servo, and how we can deal with high-current control by using transistors.
Then we'll start talking about the basics of sound generation. This is a requirement before trying to produce any sounds, even the simplest ones. This is the part where we'll describe analog and digital concepts.
At last, we'll design a very basic random synthesizer controllable using MIDI. We'll also introduce a very nice library called PCM that provides a simple way to add sample playing features to your 8-bit microcontroller.