Songs in minor keys, such as this summer's sugary hit 'Call Me Maybe,' by Carly Rae Jepsen, are on the rise as listeners want more complex sounds from their radio hits.
While there are many ways to weave emotion into music, two of the simplest are tempo and key. Happy tunes mostly have fast tempos and major keys. Sad songs often have slow tempos and minor keys.
To prove this, University of Toronto professor Glenn Schellenberg set up an experiment. He asked a graduate student to identify Top 40 songs that match these criteria. Finding happy songs from the 1960s and '70s was easy – The Beatles' "She Loves You" has a fast tempo and a major key. But with each successive decade, the hunt turned up fewer and fewer examples.
"When it came to contemporary music, it was really hard to find unambiguously happy-sounding music," says Mr. Schellenberg.
Looking at more than 1,000 Billboard hits since 1965, his team found that the average song has become longer, slower, and less happy-sounding. The share of major-key songs dropped from 85 percent of pop hits in the 1960s to just 42 percent in the 2000s.
What happened? Schellenberg says that pop culture seems to have developed an aversion to saccharin-sounding music. Many popular songs now mismatch tempo and key. By pairing mixed emotional cues, he says, artists create a more complex sound.