# A Comparison of the Effects of Binaural Beats of Audible and Inaudible Frequencies on Brainwaves
## 4 Discussion  
This study examined the effects of audible and inaudible BB stimuli on alpha power elicitation, with differences observed according to the availability of sound perception. In five brain regions, the increase in relative alpha power was significant with the BB stimulus during the stimulation phase compared with the rest phase, both with and without sound perception, and there were no differences between the states. Thus, both baseline frequencies influenced the induction of alpha waves. However, the increase in relative alpha power was greater during the audible phase than during the inaudible phase in the frontal and central areas. It has been reported that single frequency sound alone influences EEG activation. Thus, when stimuli with different single frequency sounds were presented, the brain responded differently to each stimulus [16]. In addition, there have been reports that the sounds in the inaudible frequency range affect human recognition and psychology. The alpha-wave and comfortable listening levels increased when exposed to auditory stimulation in inaudible and audible frequency ranges, rather than just the audible frequency range [17]. For BB stimuli with equal difference frequency but different baseline frequency, there was a difference in the activated brain region and the degree of activation [11,13,18]. Particularly, previous studies comparing low and high baseline frequencies (400 Hz versus 3200 Hz, 250 Hz versus 1000 Hz) with equal frequency differences [19,20] exhibited a greater effect from BB at the lower baseline frequency compared with that at a higher baseline frequency. This can be attributed to the larger evocation of the auditory steady-state response (ASSR) at the lower baseline frequencies. In this study, the difference in the reference frequency was considerably large; therefore, an extreme case with the presence or absence of sound perception was compared, and a difference in activation was observed, as in previous studies. Particularly, it could be expected that the case of sound perception induced ASSR, further highlighting the BB effect in both frontal and central regions. This showed similar results to previous studies. [PERSON] revealed that pure-tone audible alpha BB increases alpha waves in the frontal and central regions [21]. This study concludes that an increase in the alpha-power value can be induced only owing to frequency differences, even when the sound is not audible. Consequently, the pure effect of BB without the effect of sound was verified. Additionally, it has been observed that the sound factor can alter the BB effect. The ages of the subject-group participants were a limitation of this study. Considering this limitation, future research is necessary, particularly considering that ASSR is affected  
Figure 3: Increase rate of relative alpha power between audible and inaudible states at the frontal and central areas (bars represent the standard deviation). by age. Additionally, new research on the distinct mechanisms that influence the BB effect is necessary for optimizing the BB effect by comparing various baseline frequencies. In particular, it is necessary to study the cause of the EEG-induced effect observed only in specific brain regions (frontal and central) and not in other regions. Finally, research on the effects of the various components (delta, theta, and beta) beyond the alpha component is required. Conceptualization, J.-H.Y. and S.-C.C. ; methodology, J.-H.Y. and S.-C.C. ; software, M.-H.C.; validation, K.-B.K. ; formal analysis, Y.-J.K.; investigation, K.-B.K., Y.-J.K., and J.-S.K. ; resources, H.-S.K. ; data curation, M.-H.C.; writing--original draft preparation, [PERSON]-[PERSON] and S.-C.C. ; writing--review and editing, [PERSON]-H.Y. and [PERSON]-[PERSON]; visualization, M.-H.C.; supervision, S.-C.C. ; project administration, S.-C.C. ; funding acquisition, [PERSON]-[PERSON] and S.-C.C. All authors have read and agreed to the published version of the manuscript. This research received no external funding.