# Calculation of 1/f Fluctuation from Sound Signal and Comfort Evaluation
## 1 Introduction  
Noise is an undesired sound that makes people uncomfortable. Additionally, it interferes with listening to voices and music and hinders or impairs our lives [1]. Therefore, sounds that are unpleasant and disturbing to the listener are considered noise, even if they are sounds that have frequency, amplitude, or timbre [2]. It has been reported that noise causes serious problems in humans, such as causing sleep disorders [3], hindering daily life, affecting work efficiency [4], and causing hearing loss [5]. Noise, among various other types of pollution, is closely related to our daily lives, and it has several sources. Therefore, it is important to reduce the sound pressure level of noise using various noise-reduction technologies to suppress noise and establish a quiet environment. Noise control changes the acoustic state of the controlled object to the desired acoustic state via a chosen method. There are two main methods used for noise control: passive and active noise control. Passive noise control is the method of absorbing sound in a noise-transmission path to reduce the sound pressure level of noise using fiber-based materials, such as glass or rock wool, foamed metals, and ceramic granules [6]. In this method, thesound energy input to the soundproof material is converted to heat energy. Then, the reflected and transmitted energies decrease. To maximize the sound absorption coefficient of the soundproof material, it is necessary to make the thickness of the sound-absorbing material one-quarter or more of the wavelength of the noise. Therefore, when the frequency of the noise decreases, it is necessary to make the soundproof material thicker [7]. Active noise control is a method of controlling noise using the interference of sound waves from a secondary sound source [8]. This method was proposed in the 1980s and has been used in various applications with the development of digital signal processing technology [9]. Notably, active control enables wideband noise control from low-frequency to high-frequency by exploiting sound wave interference. Moreover, automobiles and electrical appliances need to provide comfortable sounds for users, and this has recently become an important factor for high-value products [10]. In previous sound design research, [PERSON] et al. [11] improved the sound quality of the camera shutter sound. Additionally, [PERSON] et al. [12] improved the quality of the hit sound and wind noise of golf clubs. These improvements provide differentiation from other companies and high value aimed at \"noise reduction\" and \"pleasant sounds\" to increase comfort. In a study on comfortable sound, participants listened to a sound signal, and subjective evaluations via a questionnaire and an evaluation via human biological signal measurements were performed [13; 14]. In a study by [PERSON] [15], the impression and comfort caused by white noise and the murmuring sound of a river were evaluated using brain waves and a questionnaire given to the experiment's participants. [PERSON] [16] evaluated the comfort of listening to a performance of an orchestra; the impression of the sound and the music output from a DVD were evaluated using a questionnaire. We considered that the evaluation of comfortable sound differs depending on the experimental environment and the preferences of the study participants who perform the comfort evaluation after listening to a sound signal. Sound evaluation is also time-consuming and costly because it is continuous and requires a large amount of data. To systematically provide a comfortable sound signal, comfort should be quantitatively evaluated. However, an effective method has not yet been established. Therefore, research is being conducted on factors and components that give people a feeling of comfort and relaxation by analyzing sound signals. It has been proven that work efficiency and comfort are affected by the tempo of sound signals [17; 18]. These studies have quantitatively evaluated the components contained in the sound signal to then evaluate comfort.