For example, it existed in the Han Dynasty a long time ago. At that time, there was no scientific phonetic notation method, and pronunciation was expressed by analogy.

Direct pronunciation: homophone phonetic notation.

Backcutting: pronounce another word with two words, take the first letter of the first word and spell it with the vowel of the second word.

Phonetic symbols, that's it: ㄅㄆㄇㄈㄉㄊㄋㄌ

Pinyin: You know.