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What does 21,000 Hz sound like?
21,000 Hz is a ultrasound frequency. It is ultrasound: above the upper limit of human hearing, although many animals – dogs, cats, bats, dolphins and rodents – can hear it.
A 21,000 Hz sound wave completes 21,000 cycles every second, so one cycle lasts 47.6 µs. In air at 20 °C, where sound travels at about 343 m/s, each wave is 1.6 cm (0.64 in) long; in water it stretches to 7.1 cm because sound moves about 4.3 times faster there.
Wavelength of 21,000 Hz in different materials
| Medium | Speed of sound | Wavelength |
|---|---|---|
| Air (20 °C) | 343 m/s | 1.6 cm |
| Fresh water | 1,481 m/s | 7.1 cm |
| Seawater | 1,500 m/s | 7.1 cm |
| Helium | 1,007 m/s | 4.8 cm |
| Steel | 5,960 m/s | 28.4 cm |
| Glass | 5,640 m/s | 26.9 cm |
Harmonics and octaves
Real instruments playing 21,000 Hz also produce harmonics at whole-number multiples of the fundamental. Their relative strength gives each instrument its timbre.
| Harmonic | Frequency | Nearest note |
|---|---|---|
| 1× (fundamental) | 21 kHz | ultrasonic |
| 2× | 42 kHz | ultrasonic |
| 3× | 63 kHz | ultrasonic |
| 4× | 84 kHz | ultrasonic |
| 5× | 105 kHz | ultrasonic |
| 6× | 126 kHz | ultrasonic |
| 7× | 147 kHz | ultrasonic |
| 8× | 168 kHz | ultrasonic |
Which animals can hear 21,000 Hz?
Can hear it
Dogs, Cats, Horses, Cows, Sheep, Pigs, Goats, Rabbits, Rats, Mice, Gerbils, Guinea pigs, Hedgehogs, Raccoons, Ferrets, Opossums, Chinchillas, Bats, Beluga whales, Bottlenose dolphins, Greater wax moths
Cannot hear it
Humans, Elephants, Chickens, Canaries, Budgerigars (parakeets), Cockatiels, Owls, Bullfrogs, Tree frogs, Goldfish, Catfish, Tuna
Frequently asked questions
What does 21,000 Hz sound like?
It is ultrasound: above the upper limit of human hearing, although many animals – dogs, cats, bats, dolphins and rodents – can hear it.
Can humans hear 21,000 Hz?
No. 21,000 Hz is above the ~20 kHz upper limit of human hearing.
What musical note is 21,000 Hz?
21,000 Hz is outside the range normally used for musical notes.
What is the wavelength of 21,000 Hz?
About 1.6 cm in air at 20 °C and 7.1 cm in water.
Can dogs hear 21,000 Hz?
Yes – dogs hear roughly 67 Hz to 45,000 Hz.