A general rule of thumb in music production is to mix multiple soundtracks so that the lead singer’s voice is in the foreground. But it’s unclear how that mix of tracks, and the intelligibility of the closely related lyrics, has changed over the years.
Scientists at the University of Oldenburg in Germany carried out an analysis of hundreds of recordings of popular songs from 1946 to 2020 to determine the lead vocal to backing ratio, or LAR. Their results appear in JASA Express Letters, published on behalf of the Acoustical Society of America by AIP Publishing, and show that, contrary to expectations, the LAR for popular music declined over the decades in question. This means that, relative to their bands, lead singers are getting quieter.
An earlier study suggested that lead vocals were mixed at a higher level than other instruments, but it looked at songs that were not fully representative of popular Western music. The current study rectified this by considering the four highest-ranking songs on the Billboard Hot 100 chart for each year from 1946 to 2020.
“Because of their diversity, the Billboard charts are considered independent and representative,” said author Karsten Gerdes.
The resulting database of 300 songs was studied by separating the voices from the sound mix on each recording. Since most recordings are not available as multiple tracks, software was used to separate each song into four tracks: vocals, bass, percussion (drums), and all other sounds. In some cases, backing vocalists were part of the recording, so the researchers developed a way to remove the influence of the backing vocals and measure only the lead singer’s level.
“Our analysis showed a significant downward trend in the LAR from about 5 decibels in 1946 to about 1 decibel in 1975, after which the LAR remained constant,” Gerdes said.
The researchers wanted to determine if the LAR values changed over time to improve the intelligibility of the lyrics or if it was due to changes in music technology. The electrical amplification of the instruments could, for example, be a factor, as could the technology of multitrack and stereophonic recording. They found that changes in music technology appear to be behind the decline seen in LAR up to 1975.
“Another possibility involves stylistic evolution within popular music,” said author Kai Siedenburg.
To test this latter idea, the researchers conducted a gender dependency study considering Grammy Award-nominated songs in the country, rap, pop, rock, and metal genres. Unsurprisingly, country had the highest LAR, followed by rap and pop. The LAR was close to zero for rock, negative for metal, and significantly higher for solo artists than for bands. Sound amplitudes were calculated by subtracting them from the maximum of the lead voice, which is why some results were negative.
“Guitar riffs are a hallmark of rock and metal, and guitars take a position comparable to lead vocals,” Siedenburg said.
This interpretation was confirmed by calculating a similar figure, the guitar-accompaniment ratio, GAR. For metal, the GAR was found to be a positive number almost equal to the LAR for pop music.
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