Humans' voice sounds more pleasant than that of primates（灵长类动物）because we don't have vocal membranes （声带膜）, a new study suggests.
Humans have vocal cords（声带）, muscles in the top of the throat, which vibrate（振动）to produce sound. That unique part helps people control their voices well enough to produce sounds that form spoken language. However, unlike all the other studied primates, humans don't have vocal membranes.
To find out how vocal membranes affected spoken sounds, a team from Kyoto University took throats from monkeys that had died of natural causes and put the parts into devices, pushing air through the throats to see how the vocal cords and membranes would react. In the experiment, the researchers found that their vocal membranes and vocal cords vibrated together.
Researchers said these vocal membranes make it harder for other primates to control the voices they make. Without these membranes, humans vocal source is more balanced, allowing better voice control and production of long and balanced voices. A key thing that distinguishes human speech from animal sounds is our control over the sounds we make.
In humans, that sort of unpleasant voices can happen when we put extreme amounts of pressure on our voice, like baby crying and adult screaming. But those are rare cases. Researchers also said that our mouths and tongues could help control the voices. They are the basis of human languages.
