soundscape

Oto-kun

Today in our comprehensive lesson, the whole class went up to the rooftop to do ear cleaning.

father

Ah, that was a good experience, wasn't it? It must be a task of quietly closing your eyes and writing down the sounds you hear. Did the teacher explain why we do such things?

Oto-kun

Yes, they said, "By being interested in the sounds around us, we can raise our awareness of a comfortable sound environment."

father

You can test your sensitivity to sound not just at concerts or special places, but in your everyday surroundings.
Have you made any new discoveries?

Oto-kun

I usually don't go up to the rooftop, but I can hear quite a few distant sounds. Especially when there are no cars on the surrounding roads, I can hear the chirping of birds from the nearby mountain, and various sounds caused by the wind, like the railing creaking and leaves rustling. These are all sounds I usually don't notice.

father

It's strange how when you concentrate on sounds, you can hear various noises. The rooftop, being a place where you can see far and wide, allows you to hear sounds that might not be audible in the schoolyard or other areas due to the shadows of buildings. Among those, were there any unpleasant sounds?

Oto-kun

Hmm, I didn't particularly find it unpleasant, but sometimes the trucks passing by were noisy. However, I discovered that there are various sounds from cars. The sound of cars passing by when the traffic light in front of the school is green is a high-pitched "shh" sound, and when the cars that were stopped at the signal start moving, a relatively low sound can be heard. I realized that this varies depending on the type of vehicle.

father

I see. You've noticed an interesting point. When a car is moving at the same speed without pressing the accelerator, the main noise outside the car comes from the contact between the tires and the road, with significant components in the range of 600 Hz to 1000 Hz. As you mentioned, when accelerating from a stop, the engine noise becomes more pronounced. The pitch (frequency) of that sound depends on the engine's rotational speed (the number of revolutions per minute).

Oto-kun

Yes, I noticed that the sound of acceleration changes in tone as the speed increases.

father

In addition to this ear cleaning, there is an activity often conducted as part of sound education called a 'sound walk,' but did you not do that?

Oto-kun

Yeah, today was just ear cleaning. What is a sound walk?

father

This is an attempt to discover sounds that are unique to a specific area by walking through it while concentrating on the sounds. Sound is not only a physical quantity like volume or pitch, but also includes subjective experiences such as pleasant sounds or sounds one does not want to hear, which people perceive sensorially. While there are mobile sound sources like cars, walking in the area can lead to the discovery of distinctive sounds that can only be heard there. Sounds that symbolize the area, as well as sounds that evoke affection or, conversely, discomfort among people, are recorded without distinction.

Oto-kun

It would be interesting to walk while measuring sound with a sound level meter.

father

That's right. But sound walks are important for sharpening people's senses by relying on their ears.

Oto-kun

I see, it's the same as ear cleaning. I tend to think that you can't understand anything unless it's quantified.

father

Until now, noise from cars and airplanes, as well as natural sounds in the environment, have been evaluated in terms of physical quantities like dB. As the saying goes, if it’s not quantified, no one can evaluate it in the same way. However, sound has both a physical aspect, which is the vibration of air, and a sensory aspect, such as pleasant or unpleasant sounds. In other words, sound can be thought of as presenting meanings that each person feels about that sound. For example, one might feel autumn in the sound of insects or a sense of refreshment in the sound of flowing water. While it is certainly important to measure and understand physical quantities, it is now being reconsidered to think about what meanings those sounds give to people before that.
A Canadian composer and researcher named R. Murray Schafer proposed the concept of soundscape, and as mentioned earlier, he demonstrated an attitude of re-evaluating the meaningful value of sound and considering the sound environment as a form of culture.

Oto-kun

Soundscape?

father

Yes, it is a coined term that applies the words used for landscape and cityscape, meaning scenery or urban landscape, to sound, resulting in the meaning of 'sound landscape.'

Oto-kun

I see, a soundscape... If we record the sounds we find during a sound walk on a map of the area, we can create a sound landscape map.

father

I see. In soundscapes, we call it a sound event map, and by creating this map of sounds, we can understand what kinds of sounds exist in that area. I think it's an important initiative to raise awareness of the sound environment among local people. The sound event map shows semantic information, but in fact, physical noise maps are also being actively created, especially in Europe. In the EU, prompted by the recognition of health risks from environmental noise, a basic common guideline for addressing noise, known as the Environmental Noise Directive, was issued in 2002, and one of its components is the creation of noise maps for areas with populations of over 250,000.

Oto-kun

Is a noise map something that measures sound and shows those values?

father

Basically, it's a calculation. By inputting various conditions such as terrain and building information, the size of the sound source, and road noise, along with traffic volume information, we calculate the sound attenuation from the sound source to the receiving point, and represent the averaged noise levels during the day and night in the residences where people live on a map.
It is common to express the magnitude of the levels using different colors.

Oto-kun

I see, the amount of noise can be represented on a map like this. It would be interesting if we could also express the meaning of the sounds.

father

That's true. In cities, the noise around the roads is loud, so even if there are unique local sounds, they are often drowned out by traffic noise. In that sense, if there were a rediscovery of these unique sounds, it would give significance to a map that expresses both the physical and meaningful aspects.