New York: 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, finds a new research. The larynx's ability to stretch vocal cords and the cords' molecular composition, show how these two characteristics of various species' larynxes can closely predict the range of frequencies each species can produce. The findings showed that larger animals had larger larynxes, and body size correlated well with the average frequency an animal could produce. The mean pitch can be correlated with size with 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 fibre structures within, the study said. At birth, vocal cords are composed of a uniform, gel-like material. As the vocal cords mature, fibres develop within the gel, eventually forming a multilayered, laminated string. The muscles in the larynx further modulate the sound the cords produce, lengthening and shortening the cords to change the pitch. For the study, published in PLOS Computational Biology, the team compiled measurements of larynx characteristics for 16 species, including humans and animals ranging from mice to elephants. 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, said Ingo Titze, scientists at the University of Utah in the US. 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.