Levitin (with little or no argument) sides with those philosophers and scientists who claim that sound (like pitch, color, and scent) is a "purely subjective fiction," rather than a mind-independent property of the world (like shape, size, motion, and number) (p. 24). The suggestion is that falling trees aren't noisy (or colorful) in themselves; rather, we impute these properties to objects as we create mental representations of vibrating molecules (sound) or experience subjective reactions to the capacity of objects to reflect light (color).
But the question of the objective, observer independent reality of these so-called "secondary properties" (color, sound) is not so easily (or rightly, in my view) dismissed. In the parlance of the debate, Levitin is a "subjectivist" with respect to these properties. "Realists," in contrast, claim that that the world would remain a noisy, colorful place were all observers suddenly to disappear. Take a look at the entry for "color" in the Internet Encyclopedia of Philosophy for a summary of the arguments on both sides.