| Hertz | Click to play |
| 200 | |
| 225 | |
| 250 | |
| 275 | |
| 300 | |
| 325 | |
| 350 | |
| 375 | |
| 400 | |
| 425 | |
| 450 | |
| 475 |
Frequency is the number of pressure waves that pass by a reference point per unit time and is measured in Hertz (Hz) or cycles per second. To the human ear, an increase in frequency is perceived as a higher pitched sound, while a decrease in frequency is perceived as a lower pitched sound. Humans generally hear sound waves whose frequencies are between 20 and 20,000 Hz. Below 20 Hz, sounds are referred to as infrasonic, and above 20,000 Hz as ultrasonic. The frequency of middle “C” on a piano is 246 Hz. You should see a more noticeable difference between 200 Hz and 225 Hz than 400 Hz and 425 Hz. Image courtesy of Submarine Ring of Fire 2002, NOAA/OER.
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