《汉书·志·律历志上》
做成十二个竹筒来听凤凰的鸣叫，其中雄的叫了六下，雌的也叫了六下，参照黄钟的音律，都可以上下相生，所以是律的根本。
制十二筒以听凤之鸣，其雄鸣为六，雌鸣亦六，比黄钟之宫，而皆可以生之，是为律本。
Twelve bamboo pipes were made to listen to the singing of the phoenix. Six of them were male and six were female. According to the musical note of Huang Zhong, they could all be generated from each other, so they were the basis of the musical note.