The rhyme of Tang poetry is consistent with the reading rhyme of Qi and Liang represented by Qieyun (this rhyme can be mutually verified with the phonetic system in Shuowen Jiezi and Yupian). At the same time, this rhyme has a good correspondence with the analysis of rhyme in the Qi and Liang Dynasties in the Southern Dynasties (of course, the rhyme of poetry can be accompanied by adjacent rhymes, but after all, the fit between this rhyme and the rhyme at that time can be analyzed from communication/transmission). From this, we can generally say that the phonology of Qieyun represents the pronunciation of Qi Liang Jiankang (now Nanjing).
On the other hand, when it comes to dialects, it may be accurate to "dialect points" rather than "dialect categories". So, although we don't know how many people in other parts of Qi Liang also speak according to Qi Kang's phonetic system, at least we can think that some people in Qi Kang speak with this phonetic system (or very close to it). After the official approval of Sui and Tang Dynasties, Qieyun had a far-reaching influence on the rhyme of poetry and local dialects. So that when we analyze the phonology of all parties now, we can take this phonology as a basic analysis point.
According to the rhyming materials and rhyming books in the Tang Dynasty, we can roughly infer the characteristics of Chang 'an phonology in the Tang Dynasty relative to the rhyming rhyme (the rhyming of Tang poetry is roughly equivalent to merging a small number of rhymes on the basis of rhyming), but the specific Chang 'an phonology may be difficult to recover. We also don't know the specific influence process of Chang 'an sound in Tang Dynasty on the local sound at that time. This is because ancient Confucian scholars paid more attention to pronunciation (especially the rhyme of poems) and did not analyze and record spoken dialects.
Compared with Qi, the golden tone of Guangzhou dialect is better in rhyme ending, such as rhyme ending-? The opposition of /-n/-m is maintained, and the ending of entering tone is maintained. However, at the specific phonetic level, all local sounds are roughly equivalent to the merger and evolution of some sounds on the basis of medieval sounds, and are no longer the face of Qi Kang Yin (for the specific face of Qi Kang Yin, please see some previous discussions and omit them here).
But at the same time, my understanding is that Chinese is essentially a * * * platform bound to the national civilization system, and local dialects are all evolutionary variants of this platform. The culture exported to people by this elegant platform through the cultural and educational system is the most important driving force for the evolution of dialects in various places. That is to say, in the traditional phonological thinking, all local sounds can be regarded as descendants of the Middle Ages Pronunciation School represented by Qi Kang.
The above is about pronunciation. As for other aspects (meaning, collocation, rhetorical effect, syntax), spoken languages of various dialects may also be regarded as descendants of written languages (including academic books and literary texts) of various dynasties. It is difficult for us to discuss what people in different areas of the Tang Dynasty usually say in spoken language, but we can understand the use of written language in the Tang Dynasty by analyzing the texts of the Tang Dynasty (including the inheritance and development of classical Chinese in the pre-Qin period and the direct use of some dialect words in the written language in the Tang Dynasty). In other words, I think that for dialects, what is more important is the part that matches the written language.