We can observe the behavior of a waveform with respect to to changes in frequency.  In the following example, you will once again see an oscilloscope depicted.  Click on the Play button and you will hear a sound.  Here you can click on buttons to change the frequency and the amplitude.  Notice what happens to the displayed waveforms when you do this, and how those changes correspond to the sounds that you hear.  As the frequency of the sound increases, the crests and troughs get closer together: a compression of the oscillation of the waveform.  Increase in frequency has the perceptual effect that the sound is "higher" in frequency.  Again, each sound is a pure electronically generated "sine" tone.