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In Japan, the bullet train causes a noise problem for residents living near the bullet train. Sound proof walls and smoothing rails have been used to solve the problem. However, it is difficult to effectively reduce the noise by them. Moreover, since the dominant components in the bullet train noise are above 2000 Hz, it is difficult to reduce them by active noise control (ANC) systems. Hence, we focus on a discomfort reduction method based on auditory masking, not a power reduction method. Auditory masking is the phenomenon that a listener does not perceive a sound with certain frequency by a band-limited noise including the critical frequency. The conventional discomfort reduction utilizes the auditory masking to reduce the discomfort due to spectral peaks in a noise. The noise has two types of discomfort due to spectral peaks and discomfort due to power fluctuation. The conventional method is effective for reducing discomfort due to the spectral peaks, but it is not effective for reducing discomfort due to the power fluctuation which is another discomfort of the noise. In this paper, we propose a discomfort reduction method by auditory masking and reduction of power fluctuation. The proposed method uses two control signals. The first signal is the same as the conventional method and used to mask the spectral peaks in the noise. Another one is used to reduce discomfort due to power fluctuation of the noise. This additional control signal is designed from the mixed signal that includes the noise and the conventional control signal. The proposed method estimates the power fluctuation period of the mixed signal and detects the high power section and the low power section of the noise. The proposed method designs the control signal by using the high power section of the noise and emits it from the secondary loudspeaker when the low power section of the noise is generated. Then, the power fluctuation of the noise becomes small. The proposed method realizes both discomfort of the spectral peaks and the power fluctuation. We carried out the subjective evaluation experiments and confirmed the effectiveness of the proposed method.
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