A sound wave, like any other wave, is introduced into a medium by a vibrating object. The vibrating object is the source of the disturbance which moves through the medium. The vibrating object which creates the disturbance could be the vocal chords of a person, the vibrating string and sound board of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker. Regardless of what vibrating object is creating the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth motion at a given frequency. The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. 

A commonly used unit for frequency is the Hertz (abbreviated Hz), where 1 Hertz = 1 vibration/second.  As a sound wave moves through a medium, each particle of the medium vibrates at the same frequency.  Certain sound waves when played (and heard) simultaneously will produce a particularly pleasant sensation when heard, are are said to be consonant. Such sound waves form the basis of intervals in music. For example, any two sounds whose frequencies make a 2:1 ratio are said to be separated by an octave and result in a particularly pleasing sensation when heard; that is, two sound waves sound good when played together if one sound has twice the frequency of the other. Similarly two sounds with a frequency ratio of 5:4 are said to be separated by an interval of a third; such sound waves also sound good when played together. Examples of other sound wave intervals and their respective frequency ratios are listed in the table below.

 The ability of humans to perceive pitch is associated with the frequency of the sound wave which impinges upon the ear. Because sound waves are longitudinal waves which produce high- and low-pressure disturbances of the particles of a medium at a given frequency, the ear has an ability to detect such frequencies and associate them with the pitch of the sound. But pitch is not the only property of a sound wave detectable by the human ear."

The Physics Classroom on Musical Instruments - http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l5a.html 

"Nearly all objects, when hit or struck or plucked or strummed or somehow disturbed, will vibrate. If you drop a meter stick or pencil on the floor, it will begin to vibrate. If you pluck a guitar string, it will begin to vibrate. If you blow over the top of a pop bottle, the air inside will vibrate. When each of these objects vibrate, they tend to vibrate at a particular frequency or a set of frequencies. The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object. If the amplitude of the vibrations are large enough and if natural frequency is within the human frequency range, then the object will produce sound waves which are audible.

Timbre 

All objects have a natural frequency or set of frequencies at which they vibrate. The quality or timbre of the sound produced by a vibrating object is dependent upon the natural frequencies of the sound waves produced by the objects. Some objects tend to vibrate at a single frequency and they are often said to produce a pure tone. A flute tends to vibrate at a single frequency, producing a very pure tone. Other objects vibrate and produce more complex waves with a set of frequencies which have a whole number mathematical relationship between them; these are said to produce a rich sound. A tuba tends to vibrate at a set of frequencies which are mathematically related by whole number ratios; it produces a rich tone. Still other objects will vibrate at a set of multiple frequencies which have no simple mathematical relationship between them. These objects are not musical at all and the sounds which they create are best described as noise. When a meter stick or pencil is dropped on the floor, a vibrates with a number of frequencies, producing a complex sound wave which is clanky and noisy. The actual frequency at which an object will vibrate at is determined by a variety of factors. Each of these factors will either effect the wavelength or the speed of the object. 

Frequency = speed/wavelength.

Harmonic

Frequency

Normalized

Note name

Closeness in %

1

440Hz.

440Hz

A

100%

2

880Hz.

440Hz

A

100%

3

1320Hz.

660Hz

E

100%

4

1760Hz.

440Hz

A

100%

5

2200Hz.

550Hz

C#

99%

6

2640Hz.

660Hz

E

100%

7

3080Hz.

770Hz

G

98%

8

3520Hz.

440Hz

A

100%

9

3960Hz.

495Hz

B

100%

10

4400Hz.

550Hz

C#

99%

11

4840Hz.

605Hz

D

103%

12

5280Hz.

660Hz

E

100%

13

5720Hz.

715Hz

F#

97%

14

6160Hz.

770Hz

G

98%

15

6600Hz.

825Hz

G#

99%