WordNet sense 1 (the amount of energy transmitted (as by acoustic or electromagnetic radiation)):

strength, intensity level

WordNet sense 2 (high level or degree; the property of being intense):

intensiveness

WordNet sense 3 (the magnitude of sound (usually in a specified direction)):

loudness, volume

WordNet sense 4 (chromatic purity: freedom from dilution with white and hence vivid in hue):

saturation, vividness, chroma