Hertz (abbreviated to Hz) is the unit of measurement of frequency or vibration. It is defined as the number of cycles per second. During speech an adult male’s vocal folds vibrate between 85 and 180Hz and an adult female’s  between 165 and 255Hz (Titze,1994). It is calculated by measuring the time in seconds between at the same point on two successive waveforms (known as a period) and dividing it into one. For example if the period measures  0.01seconds the frequency is 1/0.01seconds = 100Hz, if the period measures 0.005 of a second then the frequency is 1/0.005seconds = 200Hz. In other words the shorter the time between the waveforms the higher the frequency value.

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