The fastness or slowness of a sound is determined by its frequency. Frequency is measured in hertz (Hz) and represents the number of sound waves that pass a given point in one second. The higher the frequency, the faster the sound wave and the higher the pitch of the sound. Conversely, the lower the frequency, the slower the sound wave and the lower the pitch of the sound.

For example, a sound with a frequency of 100 Hz would be perceived as a very low-pitched sound, while a sound with a frequency of 10,000 Hz would be perceived as a very high-pitched sound. The range of human hearing is generally considered to be between 20 Hz and 20,000 Hz, although some people may be able to hear sounds outside of this range.

In addition to frequency, the speed of sound is also affected by the medium through which it is traveling. Sound waves travel faster in denser media, such as solids and liquids, than they do in less dense media, such as gases. This is why sound travels faster underwater than it does in air.