Thursday, October 25, 2007

Essential Tones Of Music Rooted In Human Speech

From Therapy Times:

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, according to researchers at the Duke University Center for Cognitive Neuroscience.

The particular notes used in music sound right to our ears because of the way our vocal apparatus makes the sounds used in all human languages, says Dale Purves, the George Barth Geller Professor for Research in Neurobiology.

It's not something one can hear directly, but when the sounds of speech are looked at with a spectrum analyzer, the relationships between the various frequencies that a speaker uses to make vowel sounds correspond neatly with the relationships between notes of the 12-tone chromatic scale of music, Purves says.

The work appeared in a recent issue of Proceedings of the National Academy of Sciences.

Purves and co-authors Deborah Ross and Jonathan Choi tested their idea by recording native English and Mandarin Chinese speakers uttering vowel sounds in both single words and a series of short monologues. They then compared the vocal frequency ratios to the numerical ratios that define notes in music.

Human vocalization begins with the vocal cords in the larynx (the Adam's apple in the neck), which create a series of resonant power peaks in a stream of air coming up from the lungs. These power peaks are then modified in a spectacular variety of ways by the changing shape of the soft palate, tongue, lips and other parts of the vocal tract. Our vocal anatomy is rather like an organ pipe that can be pinched, stretched and widened on the fly, Purves says. English speakers generate about 50 different speech sounds this way.

Yet despite the wide variation in individual human anatomy, the speech sounds produced by different speakers and languages produce the same variety of vocal tract resonance ratios, Purves says.

The lowest two of these vocal tract resonances, called formants, account for the vowel sounds in speech. "Take away the first two formants and you can't understand what a person is saying," Purves says. The frequency of the first formant is between 200 and 1,000 cycles per second (hertz) and the second formant between 800 and 3,000 hertz.

When the Duke researchers looked at the ratios of the first two formants in speech spectra, they found that the ratios formed musical relationships. For example, the relationship of the first two formants in the English vowel /a/, as in "bod," might correspond with the musical interval between C and A on a piano keyboard.