It is well known that the physical and mental stress of human is relaxed by the audible sound with 1/f fluctuation. These sounds usually have some elements, such as melody and rhythm, so, it is difficult to clarify the effect of 1/f fluctuation itself. We will verify two hypotheses: one is the 1/f fluctuation is a main factor to alleviate the physical and mental stress, and the other is the effect of 1/f fluctuation is dependent by the biological rhythm of each of human. Therefore, we investigate these hypotheses from the results of experiments based on an objective and subjective evaluation using 1/f fluctuation sound sources in ultrasonic range. And we will be able to obtain a scientific basis of physical and mental stress relaxation that is affected by 1/f fluctuation itself. In this paper, we describe the outline of these proposed methods.
