21000 Hz
Ultrasound (above 20 kHz) · E10
Turn the volume down before you play. A pure tone is harder on the ears than music at the same level.
Ultrasound
Above the human hearing range, so you will not hear it. Devices and animals may still respond.
| Wavelength | 1.6 cm |
|---|---|
| Period | 47.6 µs |
| Nearest note | E10 |
| Off by | -8 cents |
| Audible | No |
| Harmonics | 42000 Hz · 63000 Hz · 84000 Hz |
| One octave down | 10500 Hz |
| One octave up | 42000 Hz |
How to read this
- Hertz counts how many times the air vibrates per second. The bigger the number, the higher the pitch.
- Wavelength is the speed of sound (343 m/s at 20 °C) divided by the frequency. That makes 20 Hz seventeen metres long and 20 kHz under two centimetres.
- People hear roughly 20 Hz to 20 kHz, but the upper limit drops with age. Past about 15 kHz, some hear the tone and some do not.
- Hearing nothing does not mean the equipment is broken. Small speakers cannot reach the low notes, and for the high ones it is the ear that gives up first.
Frequently asked questions
Q. What does 21000 Hz sound like?
It is a pure tone vibrating 21000 times a second. It sits outside the usual human range of 20 Hz to 20 kHz, so most people will hear nothing.
Q. What is the wavelength of 21000 Hz?
1.6 cm in air. Sound travels 343 metres per second through 20 °C air, so the wavelength is that distance divided by 21000.
Q. What note is 21000 Hz?
The nearest note is E10, and it is 8 cents flat. A semitone is 100 cents, so that is about 8% of a semitone away.
Q. I cannot hear 21000 Hz — is something wrong?
High tones are the first to go with age. Most twenty-year-olds hear this pitch; past forty, many people no longer do.
Q. What are the harmonics of 21000 Hz?
The whole-number multiples: 42000 Hz, 63000 Hz, 84000 Hz. An octave up is double, 42000 Hz; an octave down is half, 10500 Hz.
Nearby frequencies
Frequency doubles for every octave, so closeness is measured in ratios, not differences.