Figure 7.11: Characteristics of sound The oscillating tuning fork (a) causes air molecules to vibrate in a manner that can be represented as a wave of pressure. Each wave contains an area in which the air molecules are more compressed (the dark regions in the upper diagram) and an area in which they are less compressed (the light regions) than normal. The peak pressure (the highest compression) of each wave defines the amplitude of the sound, and the number of waves that pass a given point per second defines the frequency. The higher the amplitude, the louder the sound; and the higher the frequency, the higher the pitch (b). All the wave drawings in this figure are sine waves, indicative of pure tones.
(Adapted from Klinke, 1986.)