Sound is produced by Vibration. The speed of a vibration is the pitch. An A note in an orchestra is tuned to 440 Hertz (that is vibrations per second). The number of vibrations per second are how the brain interprets the sound as it moves through the ear.
Vibrations travel in air or water to the ear http://oto2.wustl.edu/cochlea/intro1.htm.
Movie on Music: http://www.learner.org/vod/vod_window.html?pid=1237 (start around 8 for class)