The various degrees of pitch in the compass of the voice depend upon the
rate of vibration of the vocal cords. This rate of vibration, the
pressure of breath being the same, is caused by the different degrees of
tension of the vocal cords. If the vocal cords are drawn thin and short,
the pitch will be high; as the tension diminishes, the pitch will be
lower. The greater the number of vibrations to the second, the higher
will be the pitch. A sound consisting of sixteen vibrations to the
second produces the lowest pitch that has been recognized by the human
ear as sound; while more than 38,000 vibrations per second have not been
heard.
The lowest rate of vibration on record of any voice is about forty-four
vibrations per second, while the highest rate in any voice on record is
a little over nineteen hundred.