It has been said that sound is a number that you can hear. Vibration is the source of all sound. The result of sound is the auditory sensation produced through the ear. When a vibrating object pushes against the air around it, little zones of compressed air are created which in turn push against the air around that zone causing another zone of compressed air, which pushes against the air around that…and so on. This continues just like the ripples that form in a pool of water when a stone is thrown into the water. 

The space between the compressed air is called a rarefaction. This phenomenon can be compared to the movement of a slinky toy. This movement is repetitive and is thus called periodic motion. 

Since sound moves or travels through its surroundings such as air or water, each sound wave has a particular speed or velocity associated with it. For instance, the velocity of a sound wave at room temperature is ~ 345 meters/second. This is a little more than the length of three football fields in a second. This is difficult for the human brain to comprehend, but we know that this certainly is fast!

Think of a thunderstorm as it approaches from a distance. The distance in miles that the storm is from us is estimated by counting "one-one thousand, two-one thousand, three-one thousand,…" We begin counting when we see the flash of lightening which generates the sound that we will hear as soon as the sound wave reaches our ear. We stop counting when we hear the thunder. The total number of seconds counted represents the estimated distance in miles that the storm is from us and the distance the sound wave has traveled to reach our ear. The sound wave produced by the lightening is traveling several miles in just seconds.

In music, this speed is mathematically related to the frequency (f) and the wavelength (Y) of the sound wave.

V = f Y

If the frequency of a specific musical note at room temperature is 440 cycles per second, then the length of the sound wave is determined by substituting 345 meters per second for the velocity (V) and 440 for the frequency (f) and solving the equation for the wavelength (Y). Therefore

345 = 440 * Y

345/ 440 = Y

.784 = Y

The wavelength of this particular note is .784 meters.

Since we are interested in how sound relates to music, we are mainly concerned with sounds that produce a pure tone. Air pressure that rises and falls periodically produces pure tones. It just so happens that the pure tones produce all of our musical notes. These pure tones are all sine waves. Pure tones are the foundation of all musical sound.