Actually, the falling tree doesn't really make a "sound" at all. My understanding of the phenomena is that it’s impact only produces vibrations that, if strong enough, can be picked up by the auditory apparatus within the ear, converting the vibrations into electrical-chemical signals (neurotransmitters) to the brain. In turn, this creates the phenomenon we recognize as sound. All of our senses work that way – hearing, sight, touch, smell and taste produce those neurotransmitter signals that are sent to the brain. Within the brain, these signals are converted into chemical codes, where we assign and recognize objects. Subsequent activity sends chemical signals to other parts of the brain that reference learning and memory. A fascinating process. It would seem that our own consciousness is trapped within an isolated, internal world of a complex of neuro-chemicals that quickly shuttle about in our bodies and brains to present to us what we consider “reality”.
However, we seem to be able to discriminate the meanings of these vibrations and chemical signals and to be able to navigate about the world with other organisms with similar, physical and mental systems. Why? Because, it would seem, we have developed a conventional perspective, as well as a means to experience, these phenomena. The evolution of Earth’s higher level species from common simpler life forms provide for that convention - so that almost all species are essentially “on the same wavelength”. Our sensory abilities are all related, yours, mine, my dog’s, and my goldfish’s. That is, we all have evolved the specialized organs for sound and sight, and specialized tactile, taste and smell receptors from earlier common ancestors – as well as the brain functions that interpret the signals produced by these senses. However related though, these sensations are all very much internal – occurring solely within the brain.
Yet, in the spirit of being socially conventional and part of what is going on, I'll go along with the tree making the sound we all hear as the same. Because disregarding an objective reality would be a psychological hazard. If we only recognize the universe as “potential” phenomena that can only be interpreted through individual sensory apparatuses, our perception of it would be truly “subjective”, and utterly isolating. Then the question becomes not: "Are you really there God?" –rather, "Are you really there Bob?"