Chris Hill's "Third Ear" Wearable Lets Your Hear — or See — in Ultrasonic Frequencies

Maker Chris Hill has put together a wearable device designed to provide visualization and downsampling of ultrasonic frequencies — giving its wearer what is described as "a third ear."

"Continuing my interest in wearable augmentations that visualize phenomena, I designed a 'third ear' that enables you to listen [to] and/or visualize ultrasonic frequencies," Hill explains. "For perspective, the normal frequency range for humans is around 20Hz to 20kHz. With this third ear, you can detect frequencies between 20kHz to 100kHz, enabling brand-new sensing of your environment. The device can also enable new perspective-taking, as you can hear frequencies similar to your dog (40kHz), your cat (64kHz), or a bat (100kHz)."

The gadget, which is meant to be worn on the arm and includes a 3D-printed ear surrounding an ultrasonic microphone, is based on an off-the-shelf "Bat Detector" kit — a device designed to capture ultrasonic frequencies and downsample them to human hearing range, as a means of spotting bats as they hunt with their sonar. To this, Hill has added a 3D-printed enclosure and armband, an auxiliary breakout for a pair of headphones — and, of course, the plastic ear.

"To listen to the ultrasonic frequencies I recommend using a bone-conduction headphone to connect to the aux breakout," Hill writes. "The bone conduction creates a really interesting effect where the transformed ultrasonic frequencies are overlaid what you can hear with your biological abilities. With the device and headphones, you can explore your environment to hear what devices/things around you make sounds you can't normally hear."

For those who would prefer to see, rather than hear, in an ultrasonic range, Hill recommends a JavaScript tool based on RJ Gilmour's visualizer — turning captured audio into eye-catching circular frequency graphs.

Hill's full guide is now available on Instructables.