# Calculation of 1/f Fluctuation from Sound Signal and Comfort Evaluation
## 4 Conclusions  
This study focused on \(1/f\) fluctuation, which relieves people by masking audio signals used to reduce discomfort due to noise. We calculated the fluctuation coefficient of the sound signal and the comfort of the music, including the fluctuations given to humans.  
First, to calculate fluctuations in sound signals for masking, we used the zero-cross method and RMS to extract the frequency and amplitude components from the sound signal data. We clarified the method used to calculate the three fluctuation coefficients of the entire sound signal, such as the whole sound signal fluctuation, frequency fluctuation, and amplitude fluctuation, by discrete Fourier transform. Second, we conducted a subjective evaluation of the calculated fluctuation coefficient and human comfort. On the basis of the experimental results, we proved that the experiment's participants felt relatively comfortable with music with a frequency fluctuation coefficient close to \(-1\). Particularly for men, listening to music with a frequency fluctuation coefficient close to \(-1\) improved comfort. Moreover, on the basis of the impressive results of the music, we observed that people who felt more comfortable with music that had a frequency fluctuation coefficient close to \(-1\) tended to be comfortable when they feel Vague, Calm, and Sleepy. Therefore, it is considered that music that has a frequency fluctuation coefficient close to \(-1\) has the effect of stabilizing the mind and calming physical activity, which makes people feel comfortable. However, the study participants who felt more comfortable with music that had a frequency fluctuation coefficient far from \(-1\) chose Clear, Not Muffled, Awakening, Strong, and Powerful. Therefore, we considered that these participants tended to be comfortable when they listened to music that gave an easy-to-understand impression and had a high sound intensity.  
In future research, we will examine each calculated fluctuation coefficient and its effect on humans from the subjectivity of the participants and biological information. Therefore, we will conduct the same experiment multiple times with traceable participants and consider the changes in that tendency. Moreover, we will perform the experiment with not only frequency fluctuations but also amplitude fluctuations and sound signals with fluctuation coefficients of both a frequency and an amplitude close to \(-1\). We aim to create a sound system that provides a comfortable space by stabilizing the mind with the sound signal including fluctuation. Conversely, it provides an alarm sound when a human is drowsy or inactive in the brain. Our ultimate goal is to build a system that switches sound signals according to the situation.  
[PERSON]. ([PERSON]), [PERSON] ([PERSON]), [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], H.K., T.N. and [PERSON] wrote the manuscript; [PERSON]. ([PERSON]), [PERSON] ([PERSON]) and [PERSON] carried out the experiments; [PERSON], H.K. and T.N. contributed the analyses of the data; [PERSON]. ([PERSON]), [PERSON], [PERSON], [PERSON], H.K. and T.N. conceived Comfort Improvement by Masking of Interior Noise Using \(1/f\) Fluctuation. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
This experiment was approved by the ethics committee of Tokai University's \"Research targeted humans\".  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The study did not report any data.  
We would like to show our greatest appreciation to [PERSON].  
The authors declare no conflict of interest.