when you're in your house and hear a car drive by outside, how many different mediums do sound waves from the car engine have to travel through?

As the sound approaches, it gets louder (simply because you're closer to the source), and has a higher pitch. Then, as it passes, the sound suddenly dips down, and as it drives away you hear a lower pitch, plus a decreasing volume as the engine gets farther and farther away.

Explanation:

come closer and become far apart and become steam/gas