What makes a song sing? Backup singers

Joseph Nunes, professor of marketing at the USC Marshall School of Business, together with doctoral candidates at the USC Thornton School of Music, analyzed thousands of songs from Billboard magazine's Hot 100 list to determine which combination of instruments and vocals comprised the most popular songs in the United States over the past 55 years. The Billboard Hot 100 list began compiling hit singles in 1958.

The results of his research with Andrea Ordanini, professor of marketing at Bocconi University in Italy, were published in "I Like the Way It Sounds: The Influence of Instrumentation on a Pop Song's Place in the Charts" in Musicae Scientiae, the Journal of the European Society for the Cognitive Sciences of Music.

Voices Carry

"Using background vocals in your song increases your chances of reaching the top of the charts," said Nunes, a music lover and beginning guitarist fascinated by the psychology of music.

The researchers analyzed all 1,029 No. 1 songs on Billboard's Hot 100 between 1958 and 2012 and each of the 1,451 songs that never climbed above No. 90. They secured audio recordings of as many of those 2,480 songs as possible and employed a team of graduate students, led by Ph.D. candidate Brad Sroka, at USC Thornton to code the types of instruments and vocals audible on each.

The researchers found two combinations of core instruments and vocals most often present in No. 1 hit songs, like Prince's "Kiss" (1986) and Jay Z's "Hey Papi" (2000):

• background vocals, synthesizer and clean guitar
• background vocals, synthesizer and distorted electric guitar

The core instruments that identified songs unable to move above No. 90, such as Aretha Franklin's "Try a Little Tenderness" (1962) and Talking Heads' "Once in a Lifetime" (1986), fell into one of three combinations of core instruments:

• acoustic guitar, acoustic piano and no strings
• clean guitar and acoustic piano
• bass guitar, synthesizer and no electric piano

Even if other instruments were added to these core instruments, it did not change their likelihood of being at the top, or lingering at the bottom.

The only common thread: Every hit song featured back-up vocals, while the songs at the bottom of the charts all excluded background vocals.

A Different Tune

Nunes and Ordanini also found that the number of instruments in a song can affect its likelihood of success.

"Our results suggest songs that do not follow conventional instrumentation have the best chance of becoming No. 1 hits," Nunes said. "The average song has three to five instruments, but songs that feature a surprisingly low or high number of instruments -- at specific points in time -- tended to stand out."

This pattern synced by decade -- hits of the mid-1970s through to the '90s featured more instrumentation, while songs from the 1960s and late-2000s with fewer instruments fared better.

By coding musical pieces for different instruments, the researchers have added to the understanding of how musical properties influence preferences. Still, music is an art, not a science. They admit their analysis helps explain the success of a percentage of, but not all, hit songs.

"There are always exceptions and reasons other than the choice and number of instruments for a song's popularity," Nunes said. "For example, the star power of Rihanna may overcome any effect of instrumentation."