Product noise reduction and sound design
Oto-kun
Dad, the new printer we bought is much quieter than the old one.
father
Ah, that's right. My father thought so too. It's not noisy even when you're on the phone. The noise from electronic devices like printers and computer hard drives has been reduced, just like household appliances such as washing machines and refrigerators.
Oto-kun
Companies that manufacture home appliances and electronic devices are likely taking various measures to reduce the noise generated by their products.
father
I see. To reduce noise, various measures are taken, such as minimizing the vibrations of vibration sources like motors and mechanisms, making it difficult for vibrations to propagate through transmission paths, and suppressing the vibrations of components that radiate sound.
Oto-kun
Wow, there are various ways to reduce noise.
father
That's right. By reducing noise in that way, they ensure a quality known as 'quiet performance.' It means that it's not just about pursuing a high number of functions or high performance.
Oto-kun
I see, even though there are various features and it's a high-performance machine, if it's noisy, that alone can lower the quality of the product.
father
That's right. Therefore, the quietness of a product has become a necessary condition in a sense. However, conversely, this makes it difficult to differentiate from other manufacturers through noise reduction, and it becomes hard to showcase unique features.
Oto-kun
Has the advancement of soundproofing made it more difficult to differentiate by sound?
father
Noise reduction can be somewhat achieved by lowering the volume level quantitatively. However, if all companies aim for this, they cannot differentiate themselves through noise reduction. Therefore, equipment manufacturers are trying to create differences in the qualitative aspects of sound.
Oto-kun
Qualitative aspect? Does that mean creating a tone?
father
Yes. In sound design, I am challenging myself to create qualitatively pleasant sounds. However, the quantification of that is a challenge.
Oto-kun
Quantification of sound quality? How can that be done?
father
In the past, we compared the coarse-sounding crickets and the weak-sounding bush crickets with the sound of insects, right?
Oto-kun
Yes. The octave band analysis did not show any differences, but in the fluctuating sound analysis, wasn't the value for the fluctuating sounds of crickets high?
father
Yes, exactly. It means that differences in sound quality arose from the differences in the amount of sound fluctuations that occur periodically.
Oto-kun
Does that mean that by using fluctuation sound analysis, qualitative differences can be extracted?
father
Crickets and bush crickets produce sound by rubbing their wings together, which have fine ridges known as wing veins. The sound is generated mechanically because the wings move in the same cycle, resulting in a sound characterized by that time period.
Oto-kun
Differences in the cycle of time can make the sound feel unstable or rough.
father
That's right. The indicator that feels unsteady is called fluctuation intensity, and the rough-sounding indicator is referred to as roughness, both of which can be quantified. However, since these are sounds that fluctuate periodically, it is possible to quantify the auditory sensations that occur in accordance with their physical characteristics. The same can be said for other sound quality evaluation metrics such as sharpness (high-pitched sounds) and tonality (sounds containing pure tone components).
Oto-kun
So, conversely, what are some things that cannot be explained by auditory senses based on physical characteristics?
father
Yes, before that, the sound quality evaluation metrics I have mentioned so far are all defined by primary senses, and there is not much difference in characteristics like loudness, pitch, variability, or roughness that any listener would notice. The sensory experience that was questioned includes complex higher-order senses, such as luxurious sound, glossy sound, or rich sound, which are difficult to express with a single physical value.
Oto-kun
So, how are these higher senses evaluated and utilized in sound design?
father
Since the discussion is becoming complicated, let's save the continuation of this topic for another time. One thing that can be said is that for some primary auditory sensations, it is possible to extract physical characteristics, which are already being utilized as sound quality evaluation metrics in sound assessment and sound creation. However, for higher-order sensory quantities, the way they are perceived and evaluated varies due to individual differences, situations, and contexts, so it is necessary to conduct subjective evaluation experiments with clear conditions. The physical quantities that have a high correlation with the results of subjective evaluation experiments often become functions of various physical quantities, and it is essential to clarify those relationships.
Oto-kun
Yeah. It's a bit difficult. Please explain it to me in simpler terms next time!