Yün “is based on the Chinese philosophic concept of art as the moment when ‘the universe and the individual merge as one’ (tien jen he yi). That is when macrocosm and microcosm resonate in sympathy,” Chou explains. “The title, Yün, is taken from the expression ‘ch’i yün,’ the foremost principle in Chinese art, which means reverberation (yün) of the revitalizing force in nature (ch’i).” This Taoist concept permeates the piece, which revels in the resonances of nature. Some of these resonances are audible and include “wind and thunder, rain drops and cascades, frogs and cicadas… ” Others are inaudible. The approach to listening is clarified in Chuang Tzu: “When it cannot be heard by the ear, listen with the mind, when it cannot be heard by the mind, listen through ch’i.”
Chou employs a flexible system of variable modes to control both pitched instruments and non-pitched percussion parts to represent two “lines” in reflection of one another. All other elements also complement one another. This conforms to the yin-yang principle found in nature wherein a reflection represents an inexact shadow of the original. For example, the concave shape of one line is reflected by the convex contour of the other. These lines intermingle and “resonate” in space and time and symbolize the continual reverberations in nature.
Yün shares with another important chamber work, Pien, the same points of departure and multiplicity of ideas. However, Pien is as complex as Yün is simple.