If a tree falls in a forest and there is no one there to hear it, does it make a sound? Assuming there is actually no living being in the forest (which is not likely), the answer is no, it does not make a sound. There need to be three things present for there to be a sound:
- A source like a bird, a speaker, or a falling tree that causes vibrations;
- a medium, like air or water, for the vibration to travel through;
- an ear attached to a brain. A sound is what your brain makes out of vibrations in the medium that are sensed by the ear.
Psychoacoustics is the study of how the brain reacts to, and processes sound. The perception of sound is a very detailed, complex event. Much of how our brain handles sound is inherited, with eons of previous human experience embedded in our genetic makeup. Most of that experience was built on the need to survive. Sound was, especially at night, the primary means of knowing what was going on around you.