Sound needs to travel through something like air and water.
In fact sound travels better through solid things than it does air. Underwater you can here sound much louder and because sound travels better and faster underwater you have difficulty figuring out where the sound comes from. The reason we hear high sound and low sounds has to do with the speed in which things vibrate. The faster the vibration, the higher the sound. Nothing every made is as good at detecting sounds like your ear so treat them carefully.