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Whether your favorite band is One Direction or Slayer, you can probably tell tense chords from relaxed ones, but what exactly gives them those qualities?

Hosted by: Stefan Chin
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[INTRO ♪].

Even if you’ve never had a single music lesson, chances are certain combinations of notes, called chords or harmonies, sound prettier to you than others. Studies have found that harmonies with note frequencies that are “consonant”—meaning they’re related by a simple ratio, like octaves or perfect fifths—just seem to sound nicer than dissonant ones.

Even babies and monkeys react in ways that suggest they share these preferences. But why we like certain musical combinations isn’t completely clear. It might be how we’re wired, how we’re raised, or a bit of both.

Originally, scientists thought our preferences for certain harmonies had nothing to do with us, and had everything to do with the way sound waves interact in the air. When two sound waves are dissonant, they interfere with each other in a way that can cause an annoying “wawawa” effect sometimes called “beats. But there isn’t a good explanation for why we’d find that unpleasant.

And a 2011 study in the journal Physical Review Letters supported a different explanation: that a chord’s prettiness or ugliness is all in our heads—literally. The researchers created a simplified mathematical model of how our hearing works, and they set up a simulation of two sensory neurons listening to different tones, which would each send a signal to a third neuron when stimulated. Kind of like how different hair cells in your ears hear different pitches of sound and send a signal to your brain.

The team found that if the two sensory neurons hear what we’d normally call a “pretty” harmony, their signals arrive at the third neuron at the same time and the neuron fires once in response to the combined sound. While you’re holding the chord, that neuron has time to recharge and send a regular series of pulses. But if it’s a dissonant chord, the signals from the two sensory neurons arrive at different times, resulting in an irregularly spaced train of pulses.

So the researchers suggest that what we think of as more harmonious just means the sound causes a more regular neural pattern. According to information theory, the mathematical underpinnings of communicating information, regular signals like these communicate more information than each irregular signal does. So it could be that we think they sound better because our brains are able to distinguish and remember those signals more easily.

But even though the idea makes sense, the researchers didn’t actually test real neurons in real people. And the most recent evidence suggests that musical preferences are more strongly tied to cultural influences. In 2016, researchers surveyed a group of 64 people from the Tsimane, an Amazonian tribe that doesn’t listen to Western music and whose own music is entirely based on solo performances and contains no harmony.

When they compared the tribe members’ perceptions of sounds and harmonies to those of listeners from Bolivia and the U. S, they found that everyone in the study shared some preferences. They all liked laughter more than gasps, for example.

But while the Tsimane could hear the difference between consonant and dissonant chords, they didn’t prefer one over the other—to them, all chords sounded equally nice. This doesn’t mean that the 2011 brain model study was wrong, necessarily—just that it’s complicated, and both our biology and the music we hear when we’re young probably affect what sounds we like. Thanks to Patreon patron Evan D for asking, and to all the other patrons who voted for this question in our patreon poll.

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