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How Music Works: why are certain sounds, like feedback or nails on a blackboard, so painful?

Jennifer Van Evra

This week is CBC Music's Science Week, and all week, we will look at tech innovations that changed music, bring you the best science songs, find out how to design the perfect concert hall, meet music-making robots, check out the latest studies about music and more.

We're also going to answer questions about how much works. Can an opera singer break a glass? Can sound physically knock someone over? Why do your ears ring after a loud concert? How do horns make sound?

We'll have all the answers starting tomorrow, but here's a taste:

Why are certain sounds, like feedback or nails on a blackboard, so painful?

Just the thought of it probably makes you cringe: the dreadful, hair-raising screech of nails on a blackboard. For some people, other sounds are just as terrible, from feedback at a concert to the squeak of Styrofoam to the sound of a fork scraping on a plate.

So why do certain sounds bother us so much?

According to scientists, it likely has to do with the frequency of the sound, the fact that it happens quickly, how it's processed by our brains, plus a little conditioning.

A team of researchers at the University of Cologne studied which frequencies cause people the most pain, and what they found was surprising. It wasn’t extremely high sounds, or extremely low sounds, that hurt us most; it was the sounds that fall between 2,000 and 4,000 Hz, so still well within the range of human speech, and within the range that the human ear hears well.

Michael Oehler, a professor at the university, says our ears actually amplify sounds in that range, which may have been an evolution with a specific purpose — for example, to better hear a baby crying.

In other words, when those sounds enter, our ears actually turn up the volume.

He and his colleagues also found that our hatred of those chalkboard screeches may be partially psychological, because listeners in their study reacted less adversely when they were told the terrible sounds they were hearing were pulled from a musical composition.

What's more, a U.K. team found that the sounds tap into the part of our brains that's responsible for negative emotions, so that cringe-factor may be at least partially hardwired.

Susan Small, assistant professor of audiology at the University of British Columbia, also suspects that part of the problem is the short, sharp nature of the sound — that if our ears could have the chance to build up to it, we likely wouldn’t find it nearly as annoying.

"I think it has to do with the rise time of the sound — so things that rapidly rise to a peak seem to be more obnoxious," says Miller, who adds that short, sharp sounds also tend to do more damage to the human ear.

"What happens is we have the cochlea, which is fluid-filled, and it has the basilar membrane that runs through it, and the hair cells move with the basilar membrane. So if the basilar membrane is sharply attacked, that wave comes in with this rapid rise, it maybe sends a more concentrated signal quickly, and it just sounds more awful to us."

Make sure to check back to our CBC Music Science Week page all week for more answers, and more great stories about music and science.