Nav: Home

Pitch range produced by vocal cords

June 16, 2016

Picture a singer, accompanied by a grand piano. As the singer's voice dances through multiple octaves of range, the pianist's fingers trip from one end of the keyboard to the other. Both the singer's voice and the piano are dynamic instruments. But while the piano creates its music using the vibration of 88 strings, the singer uses only two.

According to Ingo Titze, director of the National Center for Voice and Speech at the University of Utah, vocal cords are able to produce a wide range of sound frequencies because of the larynx's ability to stretch vocal cords and the cords' molecular composition. In a new paper published today in PLOS Computational Biology, Titze and his colleagues show how these two characteristics of various species' larynxes can closely predict the range of frequencies each species can produce. The results, Titze says, reveal the evolutionary roots of how and why voice arose.

"It's absolutely amazing how nature has created a compound, laminated string to cover a pitch range that is difficult, by any stretch of the imagination, to cover with one string," Titze says.

Folds vs. cords

While most people know the structures in our throats that produce speech as "vocal cords," the term is not universally used among voice researchers. Some have preferred "vocal folds" since the mid-1970s, when studies of vocal anatomy showed a folding of the vocal ligament (the cord) during vibration. Titze says that, for the purposes of this discussion, "vocal cord" may be more apt, due to consideration of the cord's string-like properties.

At birth, vocal cords are composed of a uniform, gel-like material. As the vocal cords mature, fibers develop within the gel, eventually forming a multilayered, laminated string. Imagine a set of guitar strings glued close together with gelatin.

Fibers throughout the vocal cord layers are linked together, however, so that while some layers may be under different amounts of tension than others, the layers do not vibrate independently of each other. Returning to our guitar-strings-in-gelatin analogy, when one string is plucked, the entire gel-fiber set shakes along with it. The muscles in the larynx further modulate the sound the cords produce, lengthening and shortening the cords to change the pitch.

An animal choir

Titze and his colleagues, Tobias Riede of Midwestern University in Glendale, Arizona and Ted Mau of the University of Texas Southwestern Medical Center, compiled measurements of larynx characteristics for 16 species, including humans and animals ranging from mice to elephants. As expected, larger animals had larger larynxes, and body size correlated well with the average frequency an animal could produce.

But body size could not predict an animal's range of possible frequencies. "So, one asks, what's going on inside the larynx that allows this quite different outcome for pitch range across species, where the mean pitch is so well-correlated with size?" Titze says.

The team found that two factors were much better at predicting range: A factor measuring the amount of length change possible in the vocal cord, or how far it could stretch, and a factor measuring the stiffness of the cord due to the fiber structures within.

Titze says that creating a manmade instrument with the same properties as a vocal cord might prove technically daunting. The first step, he says, would be to fashion a laminated string, with the layers cross-linked together and supported by fluid. "But then we'd have to figure out how to pull it, elongate it, and how to distribute the tension to one layer versus another layer versus another layer," he says. "Nature has figured this out, how to literally play the dominant layer for a given pitch."

Obtaining and retaining vocal range

The results may help surgeons repair damaged vocal cords. Because both cord stretchiness and stiffness factor into range, doctors may have more options to design treatments to restore much of a patient's range. The findings also have implications for vocal training, and suggest that singers can increase their ranges by either stretching their vocal cords or by engaging in exercises that affect fiber spacing and cord stiffness - again, more options to achieve the same goal.

But Titze's investigations into vocal cord structure also reveal something more primitive. Titze says that vocalization evolved to help primates communicate over long distances by using high and loud calls. Modern human speech communication, however, does not make much use of the wide pitch and loudness range of the mammalian larynx.

That capacity is still inherent in our vocal cords, he says, but so much of our communication is electronically modulated and amplified, with even professional singers aided by microphones, that our vocal cords are rarely put to their full use.

"If you never stretch your vocal cords and never do high pitches or loud voice, eventually the ligament will atrophy into a simpler structure and you won't have that range available to you," Titze says.

A simple string

Despite the complexities of the vocal cord structure, Titze says he was surprised at how well the model of a simple vibrating string explained the cord's range. "Most people would laugh at using a simple vibrating string model for something as complicated as a 3-D, nonhomogeneous tissue structure," he says. "But the string model does an incredibly good job of explaining this range of frequencies."
-end-
This research was funded by the National Institute on Deafness and Other Communication Disorders.

This news release and an image can be downloaded from http://unews.utah.edu/pitch-range-produced-by-vocal-cords/

Once the paper publishes, the link to the live paper will be: http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1004907

University of Utah

Related Speech Articles:

Speech and language deficits in children with autism may not cause tantrums
Speech or language impairments may not be the cause of more frequent tantrums in children with autism, according to Penn State College of Medicine researchers.
What's coming next? Scientists identify how the brain predicts speech
A new study, publishing on April 25 in the open access journal PLOS Biology, has shed light on how the brain helps us to predict what is coming next in speech.
Whether our speech is fast or slow, we say about the same
Fast talkers tend to convey less information with each word and syntactic structure than slower-paced speakers, meaning that no matter our pace, we all say just about as much in a given time, a new study finds.
Do dogs of all ages respond equally to dog-directed speech?
People tend to talk to dogs as though they are human babies.
New approach may open up speech recognition to more languages
At the Neural Information Processing Systems conference this week, researchers from MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) are presenting a new approach to training speech-recognition systems that doesn't depend on transcription.
Preschoolers' expectations shape how they interpret speech
When we listen to people speak, we aren't just hearing the sounds they're making, we're also actively trying to infer what they're going to say.
Genes for speech may not be limited to humans
Mice use language but not speech, which is thought to need biological functions particular to people.
Hearing with your eyes -- a Western style of speech perception
Which parts of a person's face do you look at when you listen them speak?
When do speech difficulties in children matter for literacy?
A new study found that speech difficulties are linked with difficulties in learning to read when children first start school, but these effects are no longer apparent at 8 years of age.
Male mice model human speech defect
Male mice carrying a mutation in the Foxp2 gene have difficulty putting the syllables of their ultrasonic wooing song into proper order.

Related Speech Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...