Not to nitpick, but I think it is more accurate to say that music is composed of CHANGES in pitch, duration, tone, and volume.

To my mind, it is pitch and duration that form the melody. As for volume, tone, and sonance (certainly), I would call them "nuance."

Pitch and duration make it a melody. Add nuance and something magical happens...you have music.

This brings me in mind of those cheezy-sounding ring-tone melodies on cell phones. The have pitch and duration. And one tone, utterly lacking in musical charm. One must admit it is a melody, but due to lack of nuance, it is not very muscial at all.