fluctuating sound
Oto-kun
Since I learned about the crying dragon, I have been trying to find places at school that make sounds like it. Although not as impressive as the crying dragon of Nikko, I found several spots where clapping my hands against parallel walls produces a similar 'beep' sound.
father
Apart from the space of walls and ceilings, if I were to mention one condition for good audibility, it would be whether the place is quiet or not. The phenomenon of the 'crying dragon' involves reflected sounds that continue for a long time at regular intervals, but in a quiet place with little other noise, you can hear the decaying reflected sounds until they disappear.
Oto-kun
That's right. At early morning times, you might be able to discover the locations of the crying dragons that you couldn't hear during the day.
So far, several locations have been found, but depending on the place, the rough sound of the "bean" felt different.
So far, several locations have been found, but depending on the place, the rough sound of the "bean" felt different.
father
"You might have heard samples of continuous sounds where the sense of fluctuation increased or the roughness became prominent, depending on how many times the sound changes in one second (modulation frequency)."
Oto-kun
I see, so the time period of reflected sound differs by location, which means the way it is perceived also varies?
father
That's right. Don't you think it would be nice to quantify the sense of hearing?
Oto-kun
Is it not related to the decibels you told me about before, or something like that?
father
Decibels? Yes, dB represents a level expressed in relation to a standard. While the loudness of sound can be quantified with numerical values, quantifying the subjective experience of what we hear is quite difficult. However, there are methods to quantify certain sensory quantities, such as the feeling of sound fluctuations or the roughness we have experienced in the sounds we have heard.
Oto-kun
That sounds interesting. Can you tell me more in detail?
father
Actually, I subjected the sound of the crying dragon to a certain analysis the other day.
Look at this diagram. I won't go into detailed explanations, but this diagram has the horizontal axis representing pitch (frequency) and the vertical axis representing modulation frequency. The colors indicate the magnitude of variation. Notably, focusing on the modulation frequency, it shows that 30 Hz has the highest sense of fluctuation. In a paper from 1965 that elucidated the phenomenon of the 'crying dragon' before it was lost, there was a description of '29 reflections per second,' and indeed, this analysis proves that.
Oto-kun
Sound can be analyzed not only by level and frequency, but there are also methods of analysis like this.
father
That's right. Dad is also interested in this analysis and has tried other sounds. Interestingly, you might not know it, but it's the 'sawari' from the shamisen.
Oto-kun
"Sawari? I don't know much about the shamisen, but what does 'sawari' mean?"
father
The shamisen has three strings, but the lowest string, known as the first string, produces a sound similar to a noise by being slightly in contact with the neck without passing through the part called the upper nut, which is similar to a guitar's nut. This is a characteristic of the shamisen, and this sound is essential to the instrument.
Oto-kun
Got it! You analyzed that sound called 'bean'.
father
I see. The figure below (Figure 1) shows the results, and you can see that the fluctuation component around the modulation frequency of 140 Hz is large. Additionally, the figure below (Figure 2) is a time waveform, and as expected, there are 14 pulses in 0.1 seconds. I have a sound file of this, so give it a listen.
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Figure 1 -
Figure 2
Oto-kun
After all, it sounds like some kind of muddied sound.
father
Try listening to this sound one more time.
Oto-kun
It has a mechanical feeling, but it is very similar to the sound of the current touch.
father
This is a sound modulated at a frequency of 150Hz, extracted from a continuous 1kHz tone that I heard before.
Oto-kun
Oh, really? Is that so?
father
The frequency of the shamisen's sound can often have a significant presence in the 1 kHz range, and because the modulation frequency is close, this is why the sound can be perceived as muddy and rough.
Oto-kun
In what other cases can this analysis method be used?
father
That's right. I think it can be used to evaluate machine sounds. Machines usually generate sounds that fluctuate over time due to their consistent speed and movement. For example, when interior panels rattle in a car, it often leads to complaints about abnormal noises. It seems there are cases where such abnormal noise extraction has been utilized.
Oto-kun
I want to try out various sounds like those of different motors and the air conditioner.
father
That's right. I hope it helps to create a comfortable sound.