The concept of SN (signal-to-noise) ratio is used like common sense in the field of communication and signal processing. Recently, the term of SN ratio appears in the other fields; however, the conventional concept is too strong to understand the new concept related to the original concept. Is the SN ratio appeared in the various fields transdisciplinary concept? We discuss the similarity and the differences of SN ratio used in the fields of control, statistics and social sciences, and consider the ideal of SN ratio as a transdisciplinary technology.