Why do men in northern Shaanxi have high-pitched singing voices?

The reason why men in northern Shaanxi have sharp singing voices is due to the local geographical environment.

The mountains of northern Shaanxi have deep ravines and the residents are scattered. To communicate with each other, one must raise one's voice and shout across the gullies. Relying on lung-like pronunciation is far from enough to convey the message.

Northern Shaanxi is an old revolutionary area and the central part of China's Loess Plateau, including Yulin City and Yan'an City in Shaanxi Province. They are both in the north of Shaanxi, so they are called Northern Shaanxi.