14 DAY TRIAL // Japanese researchers at the Kyoto University discovered in a new study that certain apes have naturally mastered some of the vocal techniques that human sopranos use in the opera house. While the animals are unlikely to host a concert anytime soon, the finding does prove some insight into their evolution.
Previous studies have demonstrated that gibbons can project the sounds they make over distances of up to two kilometers (1.2 miles), regardless of the fact that they are spread out through very dense forests, a habitat that naturally muffles sounds.
Investigator Takeshi Nishimura, from the KY Primate Research Institute, in Inuyama, conducted his new study on the gibbons' vocalization abilities in a special, rather unorthodox environment. He locked one of the apes inside a box-like chamber with an unusual atmosphere.
The Japanese group exposed the white-handed gibbon (Hylobates lar) to an atmosphere containing 50 percent helium gas. Upon hearing the sounds the ape made after breathing in the chemical, the team figured out that it uses a source-filter mode of sound generation, just like humans.
Details of the research effort were published in the August 23 issue of the esteemed American Journal of Physical Anthropology. The reason why helium was used is because it allowed the team to detect the frequencies and harmonies the animal produced with its vocal folds.
The fact that these folds are used for sound generation is an amazing discovery by itself. These specialized structures generate a mixture of harmonics, each of which is a higher or lower multiple of the frequencies at which the vocal folds can vibrate.
The key discovery is that the shapes of the mouth, lips and teeth – which control the resonant frequency of the vocal tract – controlled which of the aforementioned harmonics was projected outwards.
In order to amplify the sounds they are producing, gibbons apparently put the resonant frequency of their vocal tract in tune with the pitch frequency of their vocal folds. This enables them to produce a much clearer signal, which can penetrate the thick foliage in their environment.
This process, known among musicians as resonance tuning, is part of basic training for sopranos. It is also one of the most important factors that allow a human voice to be heard over the sounds of a large orchestra.