5 sounds not meant for the human ear

HUMAN HEARING has its limits. Frequencies as high as 20,000 hertz (think of an anti-loitering alarm) can cause a pair of young ears to perk up. Any vibes above that fall into the range of ultrasound, meaning they don’t register to us at all. But gadgets like full-spectrum recorders and radio scanners have upped our auditory sensitivity and let us explore new worlds of information. Here are five shrill and mysterious noises that we’ve harnessed in some form.

A singer’s impossible peak

You might imagine Mariah Carey or Maria Callas would top the scales, but Brazilian soprano Georgia Brown set the bar by hitting a G in the high 10th octave. Musical experts later confirmed the note, which translates to about 25,000 hertz, earning Brown a Guinness World Record in 2004.

A medical device’s dramatic whine

Ultrasound machines create energy waves so fast and furious that they can pass through bone, fat, tissue, and other masses. The intensity of the transmissions depends on the medical application: Prenatal checks are usually set at 2.5 million hertz, breast scans at 5 million hertz, and skin-inflammation screenings at 100 million hertz. In some cases, extreme frequencies heal too: Pulses at 1 million to 3 million hertz have proven therapeutic for knee injuries like MCL sprains.

The cosmos’s cryptic message

In general, the universe operates in low frequencies (NASA recently recorded a black hole “screaming” at 57 octaves below the average adult voice). A mysterious radio signal from an unknown extraterrestrial location, though, screeches at such a high pitch that astronomers haven’t been able to precisely measure it. Nicknamed the “space roar,” this intense but diffuse energy wave could top out at 3 billion hertz.

A bat’s remarkable song

A diverse collection of creatures communicate in ultrasound, including katydids and hummingbirds. One species, however, takes it to a whole other level. The clear-winged woolly bat of Southeast Asia has one of the widest vocal ranges ever measured. Its echolocating buzzes can reach 250,000 hertz—more than 10 times higher than a human’s top shriek. Biologists hypothesize that the night flyers are locked in an evolutionary war with tasty moths: The higher the mammals raise their voices, the lower the chance their prey will hear them coming.

The body’s telling thrum

Heart murmurs can be a benign quirk or the sign of a deadly health condition. Family doctors might listen for them with a stethoscope, but a test called a Doppler ultrasound shows these irregular blood flows can whoosh around at up to 410 hertz, which is more than double the usual pitch. As a murmur courses through the arteries in the chest at varying speeds, the frequency of its sound changes, giving cardiologists a clue to the source’s severity.

This story originally appeared in the High Issue of Popular Science. Read more PopSci+ stories.

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Purbita Saha

Senior Deputy Editor

Purbita Saha (she/her) is the former Senior Deputy Editor at Popular Science. She led the magazine’s science desk and internship program and also edited features, read book galleys, guest starred on “Weirdest Thing I Learned This Week,” and tweeted bad jokes from the @PopSci account. She is a diehard New Jerseyan, but would move to the California desert in a flash if she had an eternal palm oasis to tend to.