The Huangyan dingsheng lu 皇言定聲錄 "Imperial Words Fixing Tones"
is a book on music compiled by the early Qing period 清 (1644-1911) collector and publisher Mao Qiling 毛奇齡 (1623-1716). The 8 juan "scrolls" long book describes the Kangxi Emperor's 康熙 (r. 1661-1722) annotations to the musical scales, and adds the author's own opinions, particularly containing critical views towards older authors. These critiques are somewhat too harsh. The main part of the book rectifies the position of altered tones for the play of the traverse (di 笛) and the vertical flute (xiao 簫). The Five Sounds (wusheng 五聲: gong 宮, shang 商, jiao 角, zhi 徵, and yu 羽) of the pentatonic scale are combined to a nine-tone scale (jiusheng 九聲) by adding the tones gongqing 宮清, shangqing 商清, jiaoqing 角清 and zhiqing 徵清. The "seven modes" (qidiao 七調) are scales based on the five tones and the altered tones biangong 變宮 and bianzhi 變徵. The emperor's studies came to the conclusion that it had been common to put the biangong tone before the gong tone in a rising scale, and the bianzhi tone before the tone zhi, which was actually wrong. The result of this custom among flute players was that the tone yu was practically used as the tone gong, and all notes in a music score had to be read as if being a transposition.
The Huangyan dingsheng lu is included in the imperial collectanea Siku quanshu 四庫全書. The edition in the collectanea Xihe heji 西河合集 (Mao Qiling's collected writings) is the original from the Kangxi reign, with supplementary paragraphs added during the Qianlong reign 乾隆 (1736-1796).
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, Changchun: Jilin daxue chubanshe, vol. 1, p. 623.