We’ve all heard the old proverb: “What we don’t know can’t hurt us.” But, as the research of emerging acoustic ecologist Kaitie Sly shows, what we can’t hear might indeed be hurting us.

Kaitie Sly in front of her interactive map

Graduating in June with a master’s in music and a specialization in music technology, the Vancouver Island born-and-raised Sly has developed a research creation project focused on the impact of inaudible human-generated sound in Greater Victoria. By creating an interactive map of the region, she has highlighted specific areas showing the location of infrasonic and ultrasonic noise.

“The point is to communicate the significance of these frequencies in our everyday lives by allowing people to experience and hear the inaudible noise that’s around us all the time,” she explains.

The sounds of silence

Infrasonic sounds exist below the human ability to hear (20 hertz and less), while ultrasonic sounds soar above our listening range (20 kilohertz and up). And while there are naturally occurring frequencies of both infrasonic (thunder, strong winds, earthquakes) and ultrasonic (tropical rainforest, bats, mice), we’re more likely to encounter them through human-generated activities like aircraft, wind turbines and ventilation systems (infrasonic) and industrial tools, wireless chargers and vehicle parking sensors (ultrasonic).

“You may hear the audible frequencies, but there’s a lot of sound happening above or below that,” she says—and therein lies the problem. “Developments in neuroscience indicate that sonic stimuli can significantly affect the human body without our awareness, which is why I wanted to study infrasonic and ultrasound specifically. There’s this assumption that what we can’t hear can’t affect us—but my research suggests that, depending on different frequencies and pressure levels, these sounds actually produce significant effects on human well-being.”

An easy comparison, says Sly, is the carbon monoxide detector. “Carbon monoxide is odorless and tasteless but it’s very dangerous, so we’ve created carbon monoxide detectors to protect ourselves. But why haven’t we done the same thing for these types of inaudible frequencies? If you have a headache, you won’t automatically attribute it to inaudible sounds—but that’s worth questioning that if you live near a highway, wind turbine, industrial centre or anti-loitering device.”

Consider wind turbines, which are known to produce infrasonic sound. “A lot of people who live near wind turbines have experienced adverse health effects—insomnia, anxiety, hypertension, panic attacks—but the turbine industry says infrasonic sound is below the audible threshold, and therefor of no consequence,” she says. “More research is needed to explore the connection between inaudible sounds and health concerns.”

Tools of the trade

Sly in the field

Sly uses a specific high-definition omnidirectional microphone that records both the infra- and ultrasonic ranges, then runs those recordings through software that reveals a spectrogram analysis of the resulting sound.

Her map project focused on data collection and analysis over a four-month period, using field recordings of specific Greater Victoria locations: the airport, the McKenzie interchange, a construction blasting site in Colwood and an antiloitering mosquito device in Sidney. The resulting map uses an interactive ripple effect to display the type and intensity of the inaudible sounds.

“One of the scary things about infrasonic sound is that we can’t really protect ourselves from it: even if we use hearing protection, it won’t stop it from having an effect on our bodies, as the soundwaves impact the entire organism,” she explains.

As an acoustic ecologist, Sly hopes to raise awareness about the impact a soundscape can have on both humans and the wider ecosystem. “Acoustic ecologists work with urban planners or landscape architects to be more aware of both the adverse and beneficial effects sound can have on our health and well-being,” she says. “It’s a field where you’re trying to find ways to harmonize humans with their acoustic environment.”

Ultimately, says Sly, we all need to be more aware of what we hear—and don’t hear—around us. “It’s not just about the risks; sound can have a very beneficial impact on our life. Whatever your profession, think about sound in everything you do.”