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Ultrasound: sound above 20 kHz
Ultrasound is sound with a frequency above about 20,000 hertz, beyond the top of human hearing. Dogs hear well into it, bats use it to echolocate, and medical scanners use frequencies in the millions of hertz to image the body. People cannot hear it at all; the highest sounds we can hear, such as the mosquito tone, sit just below it.
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Who hears ultrasound, and what uses it
| Where | Frequency | Notes |
|---|---|---|
| Dogs | Hear up to roughly 45 kHz | Which is why a dog whistle works when people hear nothing. |
| Bats | Echolocation calls above 20 kHz | Most species call well into the ultrasonic range to locate prey. |
| Medical imaging | Megahertz (millions of hertz) | Diagnostic ultrasound uses frequencies far above anything audible. |
The top of human hearing
Hearing is usually given as 20 Hz to 20 kHz, but the top end is a young person's figure. The hair cells that respond to the highest pitches wear out first, so most adults hear well short of 20 kHz. The high frequency sound test plays fixed tones from 8 kHz to 20 kHz to find your own ceiling, and the hearing age test turns that ceiling into a typical age. Below the bottom of hearing is infrasound.
Can humans hear ultrasound?
No. Hearing tops out around 20,000 Hz in young people and falls with age, and ultrasound is defined as sound above that, so it is inaudible by definition.
Is ultrasound the same as a high-pitched sound?
No. A high-pitched sound you can hear, such as the 17.4 kHz mosquito tone, is still audible sound. Ultrasound starts above the top of human hearing, around 20 kHz.
Can my phone play ultrasound?
Barely. Web audio and most phones play at 44,100 or 48,000 samples a second, which caps the highest frequency at about 22 to 24 kHz, and small speakers often stop sooner. The high frequency sound test on this site goes up to 20 kHz.
What is the opposite of ultrasound?
Infrasound: sound below about 20 Hz, too low to hear as pitch, produced by earthquakes, storms and large animals.
Sources: NIBIB, Ultrasound; Ultrasound; LSU School of Veterinary Medicine, hearing ranges; National Park Service, bat echolocation.