Pop music's not what it used to be. That’s what every generation of no-longer-kids says about what the kids are listening to, but fogey clichés aren’t necessarily wrong.

A study published in the Journal of Psychology of Aesthetics, Creativity, and the Arts tracked the mood of pop songs over five decades of Billboard charts, and it confirms that pop has changed in substantial ways. Far more of today’s hits are now in minor keys (which most of us hear as sadder or more complex) — more than half, as compared to just 15% in the 1960s.

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The study, by Glenn Schellenberg and colleagues, found that the average beats per minute fell in those decades as well. Even in uptempo dance music, minor keys are far more frequent, creating a mixed or ambiguous mood.

Why is this happening? Our reporter called up two experts, music writer Chuck Klosterman and Alice Cooper, heavy metal icon and now radio host. Cooper thinks songwriter ego bears some of the blame. “Bands that want to sound like they’re deep and serious cannot play in major keys — they want to go to minor keys to make them sound more mysterious. I think that we have really gotten away from the fun of rock music and we’ve gotten too emotional about it.”

(Originally aired: September 7, 2012)