The distance between the sound compressions and rarefactions is known as wavelength. Low frequency sounds have a long wavelength and are perceived as low-pitched sounds such as the rumble of a truck. High-pitched sounds have very short wavelengths such as sound emitted from a whistle. In the field of music a piano can generate sounds ranging from 20 cycles per second (Hz) all the way up to 4600 cycles per second.

(FIGURE 4) shows several wavelengths in feet and inches as a function of frequency.
Loudness: (Amplitude or Intensity) is measured by the strength of the sound, depicted as a sine wave above and below the normal atmospheric pressure. (Figure 5) shows the combination of sine waves the sounds at different loudness levels or amplitudes. For the sake of simplicity the sound intensity or pressure levels are measured in decibels.