Which county in Chengde, Hebei Province is the birthplace of Putonghua?

Luanping County, Chengde City, Hebei Province:

Luanping County, Chengde City, Hebei Province is only separated from Beijing by a mountain. Luanping, because of its unique historical origin, has become one of the places where Mandarin sounds are collected. From old people to dying children, everyone can speak all kinds of Putonghua, and Luanping has become a natural "Putonghua Experience Zone".

Luanping's daily language conforms to some standards about popularizing Putonghua. Luanping's pronunciation is accurate and clear, the syllables are smooth, the tone is concise, the speech speed is moderate, the airflow is coherent, it is easy to distinguish, the pronunciation is clear and clear, and the tone is slightly "hard" than that of Beijing dialect. In particular, Luanping has no pronunciation habits such as tongue rolling, word saving and ending in Beijing Hutong, so it is suitable for broadcasting, easy to speak and daily communication, so it is studied and popularized.