"The science of sound studies the communication of sound messages created by vibrations in the propagation medium. It depends on several connex domains. A sound is a physical phenomenon, but also a perceptual phenomenon. Physical attributes of a sound such as frequency and amplitude are distinct from perceptual correlate as pitch and loudness. Sounds are created by compression and expansion of gas molecule in the propagation medium"
Mathematical theory of music, Franck Jedrzejewski