The article from the four aspects of the piano sounding as percussion instrument, the original piano sound of knocking, the rhythm and dynamics of knocking sound, analyzed the various expressive ways of the piano sound of knocking in the piano works in 20th century, then to get known the feature of multifactor showed by knocking sound in those works.

Through considering the cause of formation of the knock-timbre in piano works in 20th century, the article compared two different timbre features of the piano, and got the conclusion of knock-timbre multiformity, which as writer s opinion was the theatrical base of the piano performance in 20 th century.

Influence analysis of transducers in impact-echo method by wavelet;