Sound is one of the only this in life that allows us to speak and communicate with other people. The deffinition of a human voice is; "sound produced by living beings. The source of the sound in human speaking and singing is the vibration of the vocal cords".

Sound is produced in the larynx, and the making of the sounds is called phonation. The vocal cords are set into vibration by air from the lungs that moves through the windpipe moving over them, and they make vobration in the column of air enclosed by the pharynx. The mouth and throat are different in size and shape, permitting changing of vowel sound and pitch . At puberty the vocal cords of the male become approximately double their original length, with the result that the average adult male voice is about an octave lower in pitch than the female.

Known as the voice box, the larynx is a circular chamber about 2 in. (5 cm) high, made of walls of cartilage bound by ligaments and membranes, and moved by muscles. The human larynx extends from the trachea or windpipe. In humans, part of the structure may come out noticeably at the front of the neck, creating the so-called Adam's apple.

In the larynx are the vocal cords, or vocal folds, a pair of elastic folds in the lining of mucous membrane. During breathing, the vocal cords rest along the larynx walls, leaving the air passage fully open. During speech, the cords are stretched across the larynx; air released from the lungs is forced between the cords, making them vibrate and so produce voice.

Various muscles adjust the tension of the cords, as well as the space between them, varying the pitch of the sounds produced. The more tight the cords, the higher the pitch. Since men's larynges are usually larger than women's, male vocal cords tend to be longer and the male voice is deeper. Growth may double the length of the vocal cords in the male adolescent; hence his "change of voice."

Over the vocal cords are parallel bands of protective tissue, the fake vocal cords. The larynx controls pitch and volume of vocal sounds—it produces main sounds, while the creation of these sounds results from the changing of teeth, tongue, palate, and lips. Above them, at the opening of the larynx into the throat, is the epiglottis, a flap of cartilage that helps to seal off the lower respiratory tract during swallowing so that food and other elements do not enter it.

One of the many diseases of speaking is aphasia. It is a language disturbance caused by a disruption of the brain, making an individual partially or totally impaired in his ability to speak, write, or comprehend the meaning of spoken or written words. It is distinguished from functional disorders such as stammering or stuttering, and from impaired speech due to physical defects in the organs used for speaking.

To treat is requires reeducation; the oral and lip-reading methods employed in the education of deaf and mute children have been found to be of assistance in therapy. Speech defects in children generally become apparent in the early school years. Speech problems may arise from organic or functional abnormalities, but in practice the two are often hard to differentiate.

Organic defects include deafness, cleft palate, dental abnormalities, and brain damage; most functional problems are psychological. Speech defects are generally disorders of sound production; disorders of voicing, e.g., loudness, pitch, and quality; disorders of rhythm, such as stuttering and stammering; and disorders of language creating and expression, including aphasia, the inability to use words as symbols of ideas. Treatment of a speech defect may include correction of organic conditions, psychotherapy, and training in proper speaking; it is rarely limited to a single type of therapy.