Elvis Presley, Michael Jackson, Justin Bieber… If you want to know about a generation, listen to its popular music. Songs rise to the top of the charts because they resonate with a lot of people. In fact, one way to explore cultural evolution, says researcher Jan Stupacher, is to examine trends in popular music over time.
Stupacher is a postdoc at the Center for Music in the Brain (MIB) in Denmark, a joint center of Aarhus University and The Royal Academy of Music Aarhus/Aalborg. To draw out some of these trends, Michael Hove (Fitchburg State University), Peter Vuust (MIB), and Stupacher recently studied the acoustical features of songs topping the Billboard year-end charts in the United States. Their results, reported in The Journal of the Acoustical Society of America, highlight a growing emphasis on bass in popular music.
Starting with Perez Prado’s 1955 mambo “Cherry Pink and Apple Blossom White” and ending with Justin Bieber’s hit single “Sorry,” the researchers focused on the two most popular songs of each year from 1955 to 2016; it’s quite a diverse playlist. In order to look for trends in the physical sound of the music, the researchers extracted acoustical information from each song’s 30-90 second iTunes preview clip.
Every song has a unique sound. When you strum, pluck, hit, sing, blow into, or otherwise play an instrument, you cause nearby air molecules to vibrate in a specific way. These vibrating molecules collide with their neighboring molecules, causing them to vibrate and collide with their neighbors. In this way, the vibrations—also called sound waves—travel through the air and into the ears of listeners. A sound wave is defined by its frequency (vibration rate) and its amplitude (vibration strength).
When the hammer hits the bell, the impact of the collision creates vibrations between air molecules, as seen by the ripples emitted after the impact. Those vibrations are picked up by your ear, which is how you hear the ringing. Animation: Bray Studios (via Giphy)
When the hammer hits the bell, the impact of the collision creates vibrations between air molecules, as seen by the ripples emitted after the impact. Those vibrations are picked up by your ear, which is how you hear the ringing. Animation: Bray Studios (via Giphy)
If you add up all of the sound waves produced by instruments during a song, you get a kind of sound profile of that song. From this profile, you can extract information such as a song’s total acoustical energy (an indication of its loudness), spectral range (the range of frequencies in the song and how they fluctuate over time), and the dynamic range (the difference between the quietest and loudest parts of the song). These values can then be compared from song to song.
That’s what the team did for their chosen chart-toppers. First, the researchers extracted the acoustic features of each clip. Then, they averaged the values for the two songs from the same year so that each year was represented by one set of numbers. Finally, the researchers compared how these individual features changed over time.
The result? Songs are getting louder. This doesn’t mean that people are turning up the volume louder, although that could be true too, it means that more recent songs sound louder than older songs even when they are played at the same volume. This result isn’t new or surprising, but it confirmed the results of other studies set the stage for the next part of the study.
In order to zoom in on exactly how popular music has changed over time, the researchers then divided each song into ten different frequency ranges, from the lowest (0-50 Hz) to the highest (12,800–22,050 Hz). For each range, the researchers calculated the acoustical energy and spectral flux by year. Then, they looked for trends within frequency bands over time.
Their analysis showed that popular music has been getting more bass-heavy. The two lowest frequency ranges, 0-50 Hz and 50-100 Hz, contained the biggest increases in acoustical energy over time. The researchers put it this way in their paper, “the bass boost in popular music over the last decades is clear and striking.” In fact, they show that the overall increase in song loudness over time comes primarily from an increase in lower, louder bass frequencies.
Increasing levels of bass could reflect changes in style, preference, recording technology, or a combination of factors, say the researchers. However, they emphasize that there’s a demonstrated connection between bass and movement. Research shows bass frequencies drive foot-taping, head-nodding, and dancing among listeners. The team proposes that chart-toppers might be so successful because listeners find the music so engaging, thanks to the bass-movement connection.
If you’re in the mood to get your groove on, check out The Meters. “The combination of Porter’s bass and Zigaboo’s drums just makes you want to move,” says Stupacher. “[T]heir first LP was released in 1969, before compact discs, digital workstations, and bass maximizer plugins were used. But they didn’t need them,” he says with a smile.
“Music is the best means we have of digesting time.”
-W.H. Auden quoted by Robert Craft in Stravinsky: The Chronicle of a Friendship, 1972