One of the 24 qin aesthetics is "Yuan" (rounded, circled, just right) which is talking about the vibrato on the guqin playing. The fine and subtle parts of creating a continuing sound after a pitch is reached, then continue to vibrate the string with the left hand, such as vibrato yin and nao, or zhuang, dou and huan. It was often described by ancient qin masters that the vibrato is like water ripples, or pearl running in a plate, or the rhythm we hear from chanting singing. Here I use Master Xin Xin Wang's singing of the "Southern Sound" style as an example. Listen the first 2 minutes, her voice and the flute's sound. One can hear the subtle sound motion from her singing and use that idea to relate to the vibrato on qin playing.
Later it says, "Yuan" is not only about vibrato, it also is about the left hand and the right hand's coordination. Like water drip on a lotus heart (need imagination or more observation). Just think about the Yin and Yang symbol. What is Yin and what is Yang, what is heavy and what is light, one has to define in mind.
恬Pleasing = 情到而不自擾, 意到而不自濃... 不味而味. 澹至妙來則生恬,恬至妙來則愈澹而不厭... (溪山二十四琴況)
a pleasing flavor in a primitive and plain music = a sentiment arrived but that does not bothering oneself; a feeling sensed but that one won't indulge himself or herself in.
One of the 24 Qin aesthetics - Pleasing. Came from Plain / Unsophisticated. But it does not giving no flavor, on the contrary, it creates a pleasing flavor that one never feeling tired or dislike.
雅(Elegant), 相對於俗: 喜工柔媚則俗，落指重濁則俗，性好炎鬧則俗，指拘局促則俗，取音粗厲則俗，入弦倉卒則俗，指法不式則俗，氣質浮躁則俗.
Elegant, as opposed to vulgarity which are: aiming for glamorous and seductive sound is vulgar; heavy and turbid or confused fingerings is vulgar; favor with busy sound is vulgar; Inflexible or unnatural fingerings is vulgar; unrefined and harsh sound is vulgar; hastily plucking is vulgar; not following the fingering rules is vulgar; impetuous energy is vulgar, etc.,