Gibbons have mastered some of the vocal techniques that are akin to what human sopranos rely on whilst delivering their operas. Japanese scientists have been researching them and testing their vocalizations in helium rich atmospheres.
The researchers published their findings in the journal American Journal of Physical Anthropology. Takeshi Nishimura, a primatologist at Kyoto University’s Primate Research Institute, in Inuyama, Japan and his colleagues had the unlikely idea to investigate the vocalizations of Hylobates lar, the white-handed gibbon, inside large boxes containing 50% helium gas.
Gibbons have distinctive and tuneful vocalizations that can be heard two kilometers away, through a dense forest. Just like humans, H. lar uses a source-filter mode of sound generation. The sound originates from the vocal folds as a mixture of different harmonics. The resonant frequencies of the vocal tract then determine which of these harmonics are projected.
The gibbons were recorded and this allowed the scientists to separate the different contributions of the vocal folds and vocal tracts. Helium doesn’t alter how the vocal folds vibrate, but it does shift the vocal tract’s resonant frequencies.
Gibbons tune the resonant frequency of their vocal tract to the pitch frequency generated by the vocal folds in order to amplify the sound. This type of resonance tuning is something that human singers can easily accomplish and is key to projecting their voices over loud orchestras.
Reference: “Soprano singing in gibbons” by Hiroki Koda, Takeshi Nishimura, Isao T. Tokuda, Chisako Oyakawa, Toshikuni Nihonmatsu and Nobuo Masataka, 24 August 2012, American Journal of Physical Anthropology.