Sound Research WIKINDX

"Likewise, the same account goes for sound and hearing—these too are the gods’ gifts, given for the same purpose and intended to achieve the same result. Speech (logos) was designed for this very purpose—it plays the greatest part in its achievement. And all such composition (mousikē) as lends itself to making audible musical sound (phōnē) is given in order to express harmony, and so serves this purpose as well."

On harmony:

"And harmony, whose movements are akin to the orbits within our souls, is a gift of the Muses, if our dealings with them are guided by understanding, not for irrational pleasure, for which people nowadays seem to make use of it, but to serve as an ally in the fight to bring order to any orbit in our souls that has become unharmonized and make it concordant with itself."

"A third kind of perception that we want to consider is hearing. We must describe the causes that produce the properties connected with this perception. In general, let us take it that sound is the percussion of air by way of the ears upon the brain and the blood and transmitted to the soul, and that hearing is the motion caused by the percussion that begins in the head and ends in the place where the liver is situated."

Pitch and quality - The qualities of sound, such as pitch and texture, are determined by the speed and regularity of these percussions:

"And let us take it that whenever the percussion is rapid, the sound is high-pitched, and that the slower the percussion, the lower the pitch. A regular percussion produces a uniform, smooth sound, while a contrary one produces one that is rough. A forceful percussion produces a loud sound, while a contrary one produces one that is soft."