The best-known medieval Chinese name for Tibet is Tubo (Chinese: 吐蕃 also written as 土蕃 or 土番; pinyin: Tǔbō or Tǔfān). This name first appears in Chinese characters as 土番 in the 7th century (Li Tai) and as 吐蕃 in the 10th-century (Old Book of Tang describing 608–609 emissaries from Tibetan King Namri Songtsen to Emperor Yang of Sui). In the Middle Chinese spoken during that period, as reconstructed by <answer>William H. Baxter</answer>, 土番 was pronounced thux-phjon and 吐蕃 was pronounced thux-pjon (with the x representing tone).
Who reconstructed Middle Chinese spoken from the 7th century to the 10th century?
William H. Baxter