There are two books with the title Yueshu 樂書 "Book of music", the first one written by Xin Dufang 信都芳 (mid-7th cent., courtesy name Yulin 玉琳), and the second, a kind of encyclopaedia, by Chen Yang 陳暘 (10641128, courtesy name Jinzhi 晉之). Yueshu is also the title of a treatise on music (24) in the universal history Shiji 史記.
Xin Dufang was an excellent mathematician. He became a retainer of Yuan Yanming 元延明 (484-530), the Prince of Anfeng 安豐王, together with whom he collected ancient texts on music and commented on them. When the Prince had to flee for political reasons, Xin Dufang continued this work and compiled the book Yueshu. According to the bibliographic chapter Jingji zhi 經籍志in the official dynastic history Suishu 隋書, this Yueshu was 7-juan long, but the bibliographical chapters in the histories Jiutangshu 舊唐書 and Xintangshu 新唐書 speak of 9 juan. The book thereafter was lost, but twelve fragments were collected by Ma Guohan 馬國翰 (1794-1857) from the Song period 宋 (960-1279) encyclopaedia Taiping yulan 太平御覽. One fragment deals with pitchpipes, one with ancient music, and the rest with musical instruments. They are included in Ma Guohan's reprint series Yuhanshanfang jiyi shu 玉函山房輯佚書.
Chen Yang's Yueshu was finished in 1101, after forty years of compilation. It is a sister-book to the Lishu 禮書, a compilation by Chen Yang's elder brother Chen Xiangdao 陳祥道 (1053-1093), who had originally been entrusted with the compilation of the Yueshu, but was overburdened with the two books. The Yueshu was first printed in 1199. It is 200-juan long and has a special index of 20 juan. In the first half (juan 1-95, entitled Xunyi 訓義) the author quotes extensively from the Confucian Classics about the Confucian theory and idea of music. Chen Yang annotated and explained each paragraph. The second half of the book (96-200, entitled Yuetulun 樂圖論) presents his own theory of music, with an in-depth explanation of the construction and functioning of the pitchpipes (lülü 律呂), the musical keys (gongdiao 宮調), musical forms (yuezhang 樂章) through the ages, dance, play (baixi 百戲), musical instruments, the composition of music and its use for certain court and sacrificial rituals, and the music of the "barbarian" peoples. Musical instruments are divided according to two different criteria, here the environment of their use (yabu 雅部 "instruments for elegant performances", hubu 胡部 "instruments of the barbarians", and subu 俗部 "instruments of the common folks"), and there, on a lower level, according to the material (called bayin 八音 "eight types of tone", namely metal, stone, earth, leather, silk, bamboo, gourd, and wood). The whole section describes 462 musical instruments and is richly illustrated. Also in this part, Chen quotes from older texts, and was therefore highly admired by the bibliographer Chen Zhensun 陳振孫 (Zhizhai shulu jieti 直齋書錄解題). Unfortunately the text includes quite a few errors, so that the original texts have to be used with great care.
Chen Yang's Yueshu is the oldest surviving complete text on musical theory in China, except for the Huangyou xinyue tuji 皇祐新樂圖記 that also dates from the Song period. The scholarly value of the Yueshu is therefore very high. Lou Yue 樓鑰 (1137-1213) wrote a critical commentary on the book called Yueshu zhengwu 樂書正誤. Chen Yang's Yueshu is to be found in the imperial series Siku quanshu 四庫全書.