How to tune poetry?

A tune originally belonged to one palace tune, and the musician turned it into another palace tune. For example, Yuefu Miscellanies records that Kang Kunlun, a famous pipa player in the Tang Dynasty, was good at playing the feather tune, and another rare book translated it into Fengxiangdiao with the help of the name of the pipa, which is called the mode. Tuning is a matter of music, not lyrics. But once a song is tone-sandhi, the rhythm will inevitably change, and the lyrics will also change accordingly, so there is key signature with the word "tone sandhi". Yang Wuxia's "Yi Chan" says: "You are not afraid of being heartbroken when you change your feathers and move to the palace." "molt your feathers and move to the palace", that is to say, change the tone. Dai's "Rat Spectrum" said: "Today's music is divorced from the truth, and there are still differences in tune, tone sandhi, Daqu and Xiaoqu." It is known that there is a positive tone and there may be a tone sandhi. The word "Tone sandhi" was added to the words in the Song Dynasty, including Xu Ganchen's Tone sandhi Erlang Shen. See Yuefu elegant words. This word is completely different from Erlang God written by Liu Yong. However, Tang Hui has a peaceful poem, but its title is Erlang God. Therefore, the rhyme of Wanshu is listed after Erlang God, which is called "another unity" and the word "tone sandhi" has been deleted. Wu Wenying has a poem, which is the same as that of Xu Ganchen and Tang Hui, but it is called Twelve Lang. Therefore, the sentence pattern modulated by Erlang God is different from the orthodox tone of Erlang God, and Erlang God modulation is also called Twelve Lang. It is obviously wrong for Uncle Wan to turn Erlang God into another body of Erlang God.

However, there is a guy named Ting in Li Yian, which is exactly the same as Zhou Meicheng's guy Ting (an old warbler in the wind), so I don't know why Li Yian is called Diao. Liu also has a "Mandiao" (the wind is sharp and the frost is thick), which is different from Mandiao, but the rhyme is changed to rhyme. Take this as an example, and then Jiang Baishi changed the rhyme of Manjianghong to Yunping, which can also be said to be the tone sandhi of Manjianghong. There are two butterfly lovers by Shen, which are also found in Yuefu Elegant Ci. These two words are exactly the same as butterfly lovers's tune, except that the last three words of the fourth sentence of each tune turned out to be flat, and the Shen word was changed to flat. For example, in the fourth sentence of Zhang Bi's "Die Lian Hua", it says: "Whoever moved the cymbals, Zheng moved the jade column", while Shen Ci is "full of wild colored smoke and grass", with only one pronunciation reversed. There used to be a transposed Tasha and a Zhao Yanduan. The words and expressions of these two sentences are the same, but only the first and second sentences are the same as the transposed Tasha, and the rest are different. When singing, it is by no means in tune with the Tasha line. Zhang Xiaoxiang's "Mr. Yuhu's Long and Short Sentences" refers to the tone of the palace, while Nan Gezi's three poems are based on "tone change". But tone sandhi is not the name of Gongdiao, so it is used to indicate that it is a tone sandhi Nangezi. However, the sentence syllable of this word is exactly the same as the double-folded south lattice in Ouyang Xiu's corpus, which shows that it is still in tune and is somehow marked as tone sandhi. There is also a song by an anonymous person He in Ancient and Modern Baling Ci (see Flowers and Plants Nazi Party Compilation), and its sentence pattern is different from that of Du Anshi and Ye.

Judging from the sentence patterns of Song Ci, we can only know a few examples about the difference between tone sandhi and tone sandhi, but we can't figure out the rules. Regarding this purely phonetic change, the signs in the text are not very clear.