Researchers at the Duke University Center for Cognitive Neuroscience believe that the use of 12 tone intervals in music is rooted in the physics of how our vocal anatomy produces speech. According to their research, the notes traditionally used in tonal music sound “right” to our ears because of the way our bodies make sounds used in language.
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, according to Dale Purves, Professor for Research in Neurobiology.
The researchers 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. The speech sounds produced by different speakers and languages produce the same variety of vocal tract resonance ratios, Purves said.
The lowest two of these vocal tract resonances, also known as 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 said.
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. The researchers looked at the ratios of the first two formants in speech spectra and found that the ratios formed musical relationships.
“In about 70 percent of the speech sounds, these ratios were bang-on musical intervals,” Purves said. “This predominance of musical intervals hidden in speech suggests that the chromatic scale notes in music sound right to our ears because they match the formant ratios we are exposed to all the time in speech, even though we are quite unaware of this exposure.”
Purves and his collaborators also think these findings may help explain a centuries-old debate in music over which tuning scheme for instruments works best. Ten of the 12 harmonic intervals identified in English and Mandarin speech occur in “just intonation” tuning. They found fewer correspondences in other tuning systems, including the equal temperament tuning commonly used today.