Differences in acoustics characteristics of hitting sounds in baseball games Ryohei Futamura 1 Satoshi Miharu 2 Koji Nitta 3 Kanagawa Institute of Technology 1030 Shimo-ogino, Atsugi, Kanagawa, JAPAN Takahiro Miura 4 National Institute of Advanced Industrial Science and Technology (AIST) 6-2-3 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan. Mari Ueda 5 Kanagawa Institute of Technology 1030 Shimo-ogino, Atsugi, Kanagawa, JAPAN

ABSTRACT In sports, athletes use visual and auditory information to perform full-body exercises. Some studies reported that auditory information is an essential cue for athletes: They utilized auditory information to predict ball behavior and determine body movements. However, because athletes instinctively use situation-related sounds, there is no systematic methodology to improve auditory-based competitive ability. Few studies attempted to approach the utilization of sound in games from the perspective of acoustics, and the functional acoustical features have not been quantitatively revealed. Therefore, the objective of this study is to clarify the acoustical characteristics of auditory information to max- imize its utilization in baseball games. In particular, to analyze the acoustical features of batted ball sounds that enhance defensive skills, we conducted acoustic measurements of batted ball sounds in realistic situations. The results showed that the peak gain values of fly and liner batted balls were greater than those of grounder, and the frequency components included in the hitting sound were also different among them.

1 s2185016@cco.kanagawa-it.ac.jp

2 s2185017@cco.kanagawa-it.ac.jp

3 nita@kait.jp

4 miura-t@aist.go.jp

5 m-ueda@ic.kanagawa-it.ac.jp

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1. INTRODUCTION

Sounds related to baseball games mainly include hitting sounds, catching sounds, and cheers. In sports, athletes use these various sounds to determine body movements and predict ball behavior. For example, when Shigeo Nagashima coaches Hideki Matsui over the phone, he hears only the sound of his swing and decides whether it is a good swing or a bad swing. In addition, Shohei Ohtani states that he is using sound potentially, and Ichiro says that "the sound of hitting is an important judgment factor". In this way, there is a need for professional athletes to utilize sound in sports, and auditory information such as sound is considered to be an important source of information and judgment ma- terial in sports. However, athletes often use sound sensuously, and measures to improve competitive- ness regarding sound use are not systematized. Therefore, there are few research examples that ap- proach from sound such as acoustic characteristics, and it has not been clarified quantitatively. The authors have reported on the relationship between the analysis of hitting sounds and movements in baseball competitions, and the practical use of auditory information [1-3]. As a result, it was sug- gested that sound may be utilized if the number of years of experience is long. The purpose of this study is to continue to make the best use of auditory information in baseball games and to obtain scientific knowledge for practically improving competitiveness from the sound of hitting a ball. In the previous report [4], acoustic measurements were taken at three points: 3 m behind the home base of the outdoor stadium, on the second base, and 100 m in front of the home base. In this paper, in order to clarify the acoustic characteristics of the hitting sound due to the difference in the defensive position of the outfield, the acoustic measurement of the hitting sound for 49 active baseball team members at the left, center, and right, which are the defensive positions of the outfield. Was carried out. 2. Measurement outline

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Figure 1 shows the measurement points. The measurement location is Kanagawa Institute of Tech- nology KAIT Stadium. The recording points are Point L (left): 75 m left front from the home base, Point C (center): 100 m forward from the home base, and Point R (right): 75 m right front from the home base.

Figure 1: Measurement outline diagram

3m Polat PL 10m Point © 3m Poiat R

2.1. Measurement equipment A PCM recorder (Roland, R-07) and a precision sound level meter (RION, NL-52) were installed at each measurement point 1 m above the ground (fs = 96 kHz, 16 bit). Furthermore, in order to measure the ball speed, swing speed, swing trajectory, and swing angle, a speed gun (TOA, HP-2) is installed 3 m behind the home base, and a swing meter (GARMIN x SSK, IMP001) is installed at the grip end of the bat. Was attached. The ball was a rigid ball (MIZUNO), the bat (YANASE, YUM-056) was 84.5 cm, and a 900 g wooden bat was used.

2.2. Measurement participants There are 49 male members of the Kanagawa Institute of Technology baseball club (average years of experience: 12 years) who belong to the first part of the Tokyo Metropolitan Area Baseball Federa- tion. Participants stood at bat one by one and had them batting with 10 balls per person as a guide. 3. Measurement result

The recorded hit balls were classified into eight types: left fly, center fly, right fly, left liner, center liner, right liner, short ground ball, and second ground ball. Table 1 shows the results for 41 valid data (right-handed: 38, left-handed: 3) by hitting type and hitting direction. Of the total number of hits of 334, fly: 179, liner: 79, ground ball: 76, and the average pitching speed was 92.6 km / h.

Table 1 Number of hits by hit type / direction Category Direction Frequency

Left fly 38

Fly

Center fly 80

Right fly 61

Left liner 34

Liner

Center liner 20

Right liner 25

Short grounder 49

Grounder

Second grounder 27

3.1. Eight types of hit balls and differences in noise level at each point Table 2 shows the results of the Tukey test to see if there is a difference in sound pressure level due to the difference in defensive position for each of the eight types of hitting sounds. As a result, there was a significant difference in noise level between fly and grounder in all positions, but there was no significant difference in point L-point C in the liner. In addition, the difference in fly was signifi- cantly smaller in Point L-Point C than in Point L-Point R and Point C-Point R. It is probable that the hitting sound in the left direction became louder because most of the hitters were right-handed.

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Table 2: Tukey test results

Category Point L -Point C

Point L -Point R

Point C -Point R Left fly * ** **

Center fly ** ** **

Right fly ** ** **

Left liner ** **

Center liner ** **

Right liner ** **

Short grounder ** ** **

Second grounder ** ** ** ***:p<.001 ， **:p<.01 ， *:p<.05 ， +:p<.10

Next, Figure 2 -- 4 shows the results of 1/3 octave band analysis of eight types of hitting sounds. The graph divides eight types of hitting sounds into fly, liner, and ground ball, and shows the aver- age of each hitting sound. The vertical axis shows the sound pressure, and the horizontal axis shows the frequency from 20 Hz to 20000 Hz considering the audible range. In the fly and liner graph, the blue line is the hit ball in the left direction, the orange line is the hit ball in the center direction, the green line is the hit ball in the right direction, and in the grounder graph, the blue is the short ground ball and the green is the second ground ball. From this, it was confirmed that the characteristics of the hitting sound are similar, but the values of the left and right fly and liner are larger than those of the ground ball between 1250 Hz and 2000 Hz and around 3150 Hz.

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Figure 2: Fly 1/3 octave band analysis results

SeeeRSEEREEEEE ‘Frequency (H:)

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Figure 3: Liner 1/3 octave band analysis results

Figure 4: Grounder 1/3 octave band analysis results

SEeSeRE EER ESE ELE Frequency (Hz)

3.2. Difference in angle between 8 types of hit balls and swing trajectory Figure 5 shows a boxplot of the angle of the swing trajectory for each of the eight types of hits. In the boxplot, the vertical axis is the angle of eight types of hit balls, and the horizontal axis is the angle of the swing trajectory. The Tukey-Kramer test was performed to see if there was a difference in the angle of the swing trajectory due to the difference in the hit ball. As a result, it was confirmed that there was a significant difference between the fly and the ground ball, and the liner and the ground ball (**: p <.01).

‘SPL (dB) csuesesaes’ SEeeERSSeERSE EEE “Frequency [Hz] ~

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Figure.5: Box plot of swing trajectory angles of 8 types of hit balls Next, Figure 6 shows the results of the 1/3 octave band analysis. From the test results, there was a difference between the floating ball and the non-floating ball, so for the fly and liner, the average date of the hitting sound, which is the upper swing with the swing trajectory angle from the maximum value to the third quartile, was used. On the other hand, Grounder used the average data of the hitting sound, which is the downswing of the first quartile from the minimum value of the swing trajectory angle. From here, as a feature of the hitting sound focusing on the angle of the swing trajectory, each frequency is similar in this result, but the fly and liner overlap in the vicinity of the 1250 Hz to 3150 Hz section, and the fly and liner from the ground ball. It was confirmed that the value was not a little large.

Angle of swing track [ ] “0-3 0 -$ 10 15 20 25 30 35 40 Let ay — Center fy ——- Ri —=}-—. Left liner ——_ii. Center liner —_ *p<01 Rit ine aca Short grounder + {J} —— Second grounder +E} —

Figure 6: Analysis of 1/3 octave bands for each type of ball hit

gggeegesreo tap] tas 00002 ooszi osie a8 88 Frequency (Hz} sie 02 sz 08 os sie oz

4. CONCLUSIONS

In this study, in order to clarify the acoustic characteristics of the hitting sound due to the difference in the outfield's defensive position, the acoustic measurement of the hitting sound was performed at the three points of the outfield's defensive position, left, center, and right, and the difference. I ana- lyzed the points. As a result, the way the hitting sound is heard differs depending on the defensive position of the outfield. The angle of the swing trajectory is different between the fly and the ground ball, and the liner and the ground ball. Furthermore, comparing the hitting sounds of the ground ball, fly and liner, the fly and liner contain more frequency components from 1,250 Hz to 3150 Hz than the ground ball, and the value in the section from 1250 Hz to 2000 Hz and around 3150 Hz is large. Was confirmed. From here, since the angle of the swing trajectory is different between the floating ball and the non-floating ball, in addition to the difference in the characteristics of the frequency component from the acoustic surface and the difference in the way of hearing, the hitting sound of the floating ball and the floating ball of the fly and the liner are floating. It was suggested that it may be possible to discriminate and predict the hit ball of a grounder that is not a ball. In the future, by taking a statistical approach based on data science, we are considering correcting the characteristics of the hitting sound and the error in flight distance caused by the material, weight, condition, etc. of the ball or bat. We would like to estimate more measurement participants and consider not only the measurement of right-handed batters but also the measurement of left-handed batters. 5. ACKNOWLEDGEMENTS

This research was supported by JSPS KAKENHI Grant Numbers JP18K18625 and JP21K18485, and was supported by the members involved in the baseball club of our university. 6. REFERENCES

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