As an addendum to #6... If characters in a film are made larger or smaller (a la Honey I Shrunk the Kids) their voices would change appropriately. Smaller vocal cords would produce higher frequencies at a lower amplitude. A full-size person wouldn't be able to hear somebody that was a 1/2 inch tall even if they were *in* their ear. Also, I doubt that even characters of the same size would be able to hear each other. Would your inner ear change frequency range? Would your brain even be able to interpret the sound if it did?