The amount of noise in a sound varies independently of its amplitude; you can have a nice, clean, resonant sound, thumbp!, or you can have a wheezier sound, sssshbp. In the waveform display, you've got to know how to distinguish these: noise is irregular, pitched sounds are regular. But if the degree of noisiness could be computed, it could be displayed separately; for example, a clean sound could look like this:
