That is a synth playing one note. Before we touch the synth, here is what is actually happening when you hear it.

Look at the picture. The speaker cone moves out and in, very fast. Moving out, it shoves the air in front of it together. Moving in, it leaves the air spread thin. Those bunched and thin patches roll through the room to your ear, and your ear turns them into sound. That is all sound is: air being pushed and pulled.