acoustics

Human speech is music to our ears

DUKE (US)—Humans may love music, biologically speaking, because it mimics the sounds of our own voices. Neuroscientists say the use of 12 tone intervals in the music of many human cultures is rooted in the physics of how our vocal anatomy produces speech and conveys emotion.

“There is a strong biological basis to the aesthetics of sound,” says Dale Purves, a professor of neurobiology at Duke University. “Humans prefer tone combinations that are similar to those found in speech.”

In a paper appearing in the Journal of the Acoustical Society of America (JASA), Purves says that sad or happy speech can be categorized in major and minor intervals, just as music can.

“Our appreciation of music is a happy byproduct of the biological advantages of speech and our need to understand its emotional content,” Purves says.

In a second paper appearing Dec. 3 in the online journal PLOS One, Kamraan Gill, another team member, reports that the most commonly used musical scales are also based on the physics of the vocal tones humans produce.

Purves says the evidence suggest the main biological reason we appreciate music is because it mimics speech, which has been critical to our evolutionary success.

To study the emotional content of music, the team collected a database of major and minor melodies from about 1,000 classical music compositions and more that 6,000 folk songs and then analyzed their tonal qualities.

They then had 10 people speak a series of single words with 10 different vowel sounds in either excited or subdued voices, as well as short monologues.

The team compared the tones that distinguished the major and minor melodies with the tones of speech uttered in the different emotional states.

They found the sound spectra of the speech tones could be sorted the same way as the music, with excited speech exhibiting more major musical intervals and subdued speech more minor ones.

The tones in speech are a series of harmonic frequencies, whose relative power distinguishes the different vowels. Vowels are produced by the physics of air moving through the vocal cords; consonants are produced by other parts of the vocal tract.

In the PLOS One paper, the researchers argue the harmonic structure of vowel tones forms the basis of the musical scales we find most appealing. They show the popularity of musical scales can be predicted based on how well they match up with the series of harmonics characteristic of vowels in speech.

Although there are literally millions of scales that could be used to divide the octave, most human music is based on scales comprised of only five to seven tones. The researchers argue the preference for these particular tone collections is based on how closely they approximate the harmonic series of tones produced by humans.

Though they only worked with western music and spoken English, there is reason to believe these findings are more widely applicable. Most of the frequency ratios of the chromatic musical scale can be found in the speech of a variety of languages.

Their analysis included speakers of Mandarin Chinese, says neuroscience graduate student Daniel Bowling, who is the first author on the JASA paper, and this showed similar results.

It would be hard to say whether singing or speech came first, but Bowling supposes “emotional communication in both speech and music is rooted in earlier non-lingual vocalizations that expressed emotion.”

Duke University news: www.dukenews.duke.edu/

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