14 DAY TRIAL // How you speak is connected to how you feel music, as a team at the Duke University Center for Cognitive Neuroscience has discovered. "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," said 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 said.
Purves's team checked this by recording native English and Mandarin Chinese speakers uttering vowel sounds in both isolated words and short monologues. The vocal frequency was compared to the frequency of musical notes. The vocal cords in the larynx induce a series of resonant power peaks in an air flow rising from the lungs. The peaks can be changed in an indefinite number of ways by shape changes of the soft palate, tongue, lips and other zones of the vocal tract. "Our vocal anatomy is rather like an organ pipe that can be pinched, stretched and widened on the fly. 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 said.
English speakers emit roughly 50 different speech sounds. The two lowest vocal tract resonances, named formants, determine the vowel sounds in speech. "Take away the first two formants and you can't understand what a person is saying," Purves said.
The first formant has a frequency of 200 - 1,000 hertz and the second formant of 800 - 3,000 hertz.
The speech spectra revealed that their ratios in speech were the same as in musical relationships. "In about 70 % of the speech sounds, these ratios were bang-on musical intervals. 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", said Purves.
Only modern experimental pieces apply all 12 tones. Most music genres employ just the 7-tone scale to divide octaves, and most folk music employs just five tones.
The team is investigating if a given culture's preference for one subset of the tones over another is linked to the relationships dominant in the native language. "Equal temperament tuning, in which each of the 12 interval distances in the chromatic scale is made exactly the same, is a scheme that enables an ensemble such as an orchestra to play together in different keys and across many octaves. Although equal temperament tuning sounds pretty good, it's a compromise on the more natural, vocally derived just intonation tuning system," Purves said.
"The group's next study concerns our intuitive understanding that a musical piece tends to sound happy if it's in a major key but relatively sad if it's in a minor key. That, too, may come from the characteristics of the human voice", he speculates.