Yín and Náo (two kinds of Vibrato) are natural rhythm movement. They are like some kind of breathing pulsation, and are parts of the musical language composition of the guqin. They are existing naturally on their own, at all times and in all places, in a qin music. They are more obvious at a note with longer duration. If one observes a qin player's appearance of playing, one will see the player vibrating his or her fingers from time to time. The range of those vibrato motions can be big and obvious, or subtle and almost not showing, no matter if the tablature has indication of the Yín and Náo or not.
The beats situation of the Qin music in general, are “Sǎn bǎn” (Rubato) and “Rù pāi” (entering the beats). However, there is a correlation of “Sǎn bǎn” and “Rù pāi” in the variable rhythm and beats of the qin music. In “Sǎn bǎn”, there could have some subtlety of “Rù pāi” existed, vice versa. And yet, Yín and Náo are existed in the musical process, both in “Sǎn bǎn” and “Rù pāi,” by adjusting the different ways of pulsing. “Rù pāi” has more regular pattern of beats and is more balanced in rhythm than “Sǎn bǎn.”
There is one finger technique of the qin, called "Bù dòng" (without moving). Usually means that the indicated finger stays there without moving until the next note had been played, then using that stable finger again to play the following note. Or it can just simply means "don't move." If Yín and Náo are reflecting the left hand vibrato movements, places where no indication of Yín and Náo should mean no vibrato movement. Why did ancient people not using a "Bù dòng" notation to indicate that there is no vibrato? But only indicate Yín and Náo at certain places? That is because ancient qin masters think that to indicate Yín and Náo at important places to show it is very important and indispensable, otherwise, it is always there. So no indication of Yín and Náo does not mean by "Bù dòng."
Another two finger techniques, Chuò and Zhù (sliding down and sliding up) has the same situation of not indicated on every note but only on important and indispensable notes. Chuò, Zhù andYín, Náo are correlated. Sometimes, Chuò or Zhù happened after Yín or Náo; sometimes Yín or Náo happened after Chuò or Zhù. One will notice that almost all the qin masters used more Chuò and Zhù than what the qin tablature had indicated. Because Chuò, Zhù, Yín and Náo, are the techniques to create variety of the rhythm and sound color of the qin, it achieves the qin music to a very rich, deep and mystery level.