Frequency

The frequency of a sound is the number of cycles of a sound wave in one second. The unit of measurement is hertz (Hz). The frequency of a sound increases as the number of cycles per second increase. 

Vibrations between 20 and 20,000 cycles per second are interpreted as sound by a normal healthy person. A high-pitched sound could be a piccolo flute or a bird singing. Low-pitched sounds could be thunder heard from far away or tones from a bass guitar.