Imagine a scenario. A criminal is being tried in court. He denies saying something. The prosecution brings a recording, saying they have his confession on tape. As the accused vigorously denies the voice being his, an expert shows just why the voice could be no one else’s.
A fictional scene? Perhaps, but it is a reality that no two persons in the world have exactly the same voices. Do you know why this is so?
The act of speaking involves movements of hundreds of muscles in split-second coordination. The speech organ called larynx or voice box is capable of producing an infinite number of sounds. It is that part of the throat through which air passes. When we breathe, air passes through the larynx downwards, through the mouth and nose, into the trachea (windpipe) and finally to the lungs.
The larynx is made up of a tough wall of cartilage. Its inside lining has two folds of tissue stretching on each side and leaving a gap between them. These are called vocal cords. When a person is quiet and breathing, the gap between the cords remains wide open. The cords are slack.
But talking, singing or shouting involves the tightening of the cords; the exhaled air causes the cords to vibrate and produce sound. Our vocal cords can be in any of about 170 different positions.
If the vocal cords are slack, they may vibrate about 80 times per second and the result is deep tones. If they are tense, they vibrate rapidly, perhaps a 1000 times a second, and produce short sound waves or high tones.
As a child has short vocal cords, they produce short air waves and consequently a high pitched voice. As a child grows, the vocal cords become longer. That causes the voice to become deeper. Thus,k the voices of adults are heavier and deeper than children’s voices.
Similarly, the voice of most adult men is deeper than those of women. This is because a man’s larynx is larger than that of a woman. It also has longer cords.
The pitch of voice depends upon the length of the vocal cords. Each voice has a certain range of frequencies. It is this range that determines the kind of voice a person has. Voices can be divided into six groups: bass, baritone, and tenor for men, and alto, mezzo soprano and soprano for women.
The quality of human voice also depends on many other things such as resonating space, lungs, nasal cavities etc. The nose, sinuses, pharynx and oral cavity act as resonating chambers and modify the vocal tone produced by the vocal cords.
The movement of the tongue against the palate, the shaping of the lips and arrangement of teeth also bring about changes in the voice. Since the structures and movements of all these organs are different in different persons, the voices of no two persons in the world can be identical.