If all sound is caused by vibration, why is one sound simply a noise and another sound pleasing or musical? The answer is that it depends on how the sound-making object vibrates. When the vibration is very regular (that is, when the sounding body sends out waves at absolutely regular intervals), the result is a musical sound. If the vibration is not regular, or very sudden, the effect on our ears makes us call it a noise.

Sounds differ in many ways. We know, for example, when a sound is near and when it’s far away. We can also tell that certain sounds are high and shrill and others are deep and low. And we can tell the sound of one musical instrument from another. Well, these three differences between one sound and another are loudness, pitch, and tone quality.