Comfortable Sound Design Based on Auditory Masking with Chord Progression and Melody Generation Corresponding to the Peak Frequencies of Dental Treatment Noises  
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case of indoor noise that includes high-frequency noise, such as that from air conditioning units, this tendency is notable [5]. Examples of noisy environments with noise containing peak frequencies include factory noise and railway brake noise. Additionally, dental treatment noises with high-frequency noise cause strong unpleasant and fearful feelings in many patients and doctors [6; 7]. It is considered that such low-power noise problems cannot be solved only by reducing the sound pressure level of the noise. Our research thus focuses on reducing sound that causes unpleasant feelings not by reducing the noise power but by adding masker signals to the noise based on auditory masking. Auditory masking is one of the auditory properties of the human ear, and it is the phenomenon in which one sound is drowned out by another sound. It has been studied using various methods [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. In addition, research has been conducted to elucidate the mechanisms behind pleasant sounds [24; 25; 26; 27; 28; 29; 30; 31; 32; 33] and on comfortable sound design [34; 35; 36; 37]. We have also found that there is a trade-off between sound design for comfort and for reductions in discomfort [38]. We have proposed auditory-masking-based discomfort reduction methods for various noisy environments, such as fan noise [39], factory noise [40], railway brake noise [41], and dental treatment noise [42; 43; 44; 45; 46; 47]. These methods designed masker signals using a band-pass filter with the critical bandwidth [48]. In methods [42; 43], auditory masking that corresponds to the peak frequencies of the noise is applied, achieving good performance in reducing discomfort. However, these methods struggle to create pleasant sounds due to the lack of comfort in the masker signals. In this study, we focus on music as a source of pleasant sound. According to music theory, music consists of three elements: rhythm, melody, and harmony [49; 50; 51; 52; 53]. In conventional methods [44; 45; 46; 47], we proposed comfortable sound design based on forming single chords for dental treatment noises. However, the conventional methods had difficulty adapting to variations in the peak frequency of the dental treatment noises because they only used the Canon progression as the chord progression. Furthermore, we previously proposed comfortable sound design using only chord progressions to mask dental treatment noises [38]. However, this method [38] encountered challenges in improving comfort scores due to the trade-off between pleasant sound design and effectively reducing discomfort. In this paper, we propose comfortable sound design based on auditory masking with the melody and harmony (chord progression) matched to the peak frequency of the dental treatment noise. The chord progression sounds are generated using major triads of sawtooth waves and the music theory of diatonic chords.