If in the past there were many documents and books written about A Dao (or Ca Tru) from the perspective of history, literature or research on Sino-Nom documents, then in A Dao: A study of history and ryles of sound system, author - music researcher Bui Trong Hien chose a different approach. That is to delve into the historical aspects, cultural space and sound system of this traditional art form. Reading the book, readers will step by step enter the artistic world, imbued with the Vietnamese cultural spirit of A Dao singing, and understand why this type of music is recognized by UNESCO as an intangible cultural heritage of the world.