The essential tones of human music are rooted in the physics of how our vocal cords produce speech, according to a study published Friday.

Researchers at Duke University's Center for Cognitive Neuroscience found that particular notes sound right to our ears because of the way our vocal apparatus makes the vowel sounds used in human languages.

Humans can't hear it directly, but when the sounds of speech are looked at with a spectrum analyzer, the relationships between the frequencies produced in the throat correspond with the relationships between notes in the 12-tone chromatic scale of music, said Dale Purves, the George Barth Geller Professor for Research in Neurobiology.

When humans speak, our vocal cords vibrate to create "peaks" of resonant sound in air coming from the lungs that can be modified by the way we change the shape or position of our tongue, lips, soft palate or throat.

The two lowest vocal tract resonances, called formants, are used to produce vowels, said Purves.

"Take away the first two formants and you can't understand what a person is saying," Purves said.

The frequency of the first formant is between 200 and 1,000 cycles per second (hertz) and the second formant is between 800 and 3,000 hertz.

When a speaker produces a vowel sound, it resonates on the two frequencies, with each vowel producing a different ratio between the frequencies. Purves said these ratios match up consistently with the ratios in musical tuning.

For example, the relationship between the two frequencies produced in the English vowelfound in "bought"might match up with the musical interval between C and A on a piano keyboard, Purves said.

Purves and co-authors Deborah Ross and Jonathan Choi tested the idea by recording native English and native Mandarin Chinese speakers uttering vowel sounds in both languages and comparing those sounds and their frequency ratios to the numerical ratios found in music.

They say the results could help explain why some cultures prefer one kind of music to another, particularly if differences in vowel sounds found in thelanguages produce different resonances.

The study was published Friday in the online version oftheProceedings of the National Academy of Sciences.