Sui and Tang Dynasty. During this period attempts were made to codify playing techniques and notation. Based on the detailed description in the essay "Qin Cao" 【琴操】 by Cai Yong (132–192), the standard form of the qin was most likely set around the late Han Dynasty. The earliest surviving qin in this modern form, preserved in both China and Japan, have been reliably dated to the Tang Dynasty. Many are still playable, the most famous perhaps being the one named "Jiuxiao Huanpei" 《九霄環佩/九霄环佩》, attributed to the famous late Tang Dynasty qin maker Lei Wei (雷威). It is kept in the Palace Museum in Beijing. The earliest known piece of notated guqin music, Jieshi Diao Youlan, dates from this period. In the third period, guqin compositions proliferated and the playing techniques were refined. The Song Dynasty is considered the golden period of guqin music, with numerous poems and essays on guqin written by the literati, and many well-known pieces can be dated to this period. Treaties and handbooks were also written, documenting its music and playing techniques, and aesthetic consideration also became the most important aspect of guqin playing in this period. Modern times In 1977, a recording of "Liu Shui" 【流水】 (Flowing Water, as performed by Guan Pinghu, one of the best qin players of the 20th century) was chosen to be included in the Voyager Golden Record, a gold-plated LP recording containing music from around the world, which was sent into outer space by NASA on the Voyager 1 and Voyager 2 spacecraft. It is the longest excerpt included on the disc. In 2003, guqin music was proclaimed as one of the Masterpieces of the Oral and Intangible Heritage of Humanity by UNESCO. Mentions in Chinese literature When consulting ancient and medieval Chinese texts, one will come across frequent references to the qin. Such references are particularly frequent in Classical Chinese poetry, such as the poetic verses of the ancient Shijing and certain poems of the Tang period. Ancient poetry In the Shijing 【詩經】 (Book of Songs), several poems mention the qin (with their numbers according to their order in the anthology): 「窈窕淑女， 琴瑟友之。」 "Fair and gentle is the maiden; Use qin and se to give her a friendly welcome..." [《關睢》 1] 「琴瑟在御， 莫不靜好。」 "The qin and se in your [the husband's] hands; Will emit their quiet pleasant tones..." [《女曰雞鳴》 82] 「我有嘉賓， 鼓瑟鼓琴。」 "I have fine guests; So I