Product noise reduction and sound design

Dad, the new printer we bought is so much quieter than the old one.

Ah, yeah. My dad thought so too. It's not noisy even when he's on the phone. The noise from electronic devices like printers and computer hard drives has been reduced, just like with household appliances like washing machines and refrigerators.

Companies that manufacture home appliances and electronic devices probably take all sorts of measures to reduce the noise they make.

That's right. To reduce noise, various measures are taken, such as reducing the vibration of the source of vibration, such as the motor and mechanical parts, making it more difficult for the vibration to be transmitted through the pathways along which it is transmitted, and suppressing the vibration of parts that radiate vibration as sound.

Wow, so there are various ways to reduce noise.

That's right. By reducing noise in this way, they ensure the quality of "quiet operation." It's not just about pursuing a lot of features or high performance.

I see, even if a machine has many features and is high-performance, if it's noisy, that alone can lower the quality of the product.

That's right. So, in a sense, quietness in products is becoming a necessary condition for products. But conversely, if that's the case, it becomes difficult to differentiate from other manufacturers through noise reduction alone, and it becomes difficult to create a distinctive feature.

Does this mean that as noise reduction progresses, it has become more difficult to differentiate products based on sound?

Reducing noise can be achieved to some extent by quantitatively lowering the noise level. However, if every company aims for the same thing, they won't be able to differentiate themselves through noise reduction alone. Therefore, equipment manufacturers are trying to differentiate themselves in terms of sound quality.

Qualitative aspects? Does that mean creating a specific tone?

That's right. I'm working on sound design, which is about creating sounds that are qualitatively pleasing. But quantifying that is the challenge.

Quantifying sound quality? How can that be done?

I remember we previously compared the sounds of insects, specifically crickets, which have a rougher sound, and bell crickets, which have a weaker sound.

Yeah. There was no difference in the octave band analysis, but wasn't the value for the cricket's fluctuating sound higher in the fluctuating sound analysis?

That's right. The difference in the amount of fluctuation in the periodically changing sound resulted in a difference in sound quality.

Does this mean that we can extract qualitative differences using fluctuating sound analysis?

Crickets and bell crickets produce sound by rubbing their wings together, which have fine, uneven ridges called wing veins. Because they mechanically move their wings in the same period, the sound they produce is characterized by that time period.

Differences in the time cycle can make the sound seem shaky or rough, right?

That's right. The indicator for a wavering feeling is called fluctuation intensity, and the indicator for a rough feeling is called roughness, and both can be quantified. But because it's a sound that fluctuates periodically, we can quantify the auditory sensation that arises from its physical characteristics. The same can be said for other sound quality evaluation indicators such as sharpness (high-pitched sound) and tonality (sound containing pure tone components).

So, conversely, what are some things where auditory sensation cannot be explained by physical characteristics?

Well, before that, the sound quality evaluation indicators I've mentioned so far are all defined as primary senses, and things like volume, pitch, variability, and roughness don't make much difference to anyone who listens. The senses you asked about involve complex, higher-order senses, and things like high-quality sound, rich sound, and full-bodied sound are difficult to express physically with a single numerical value.

So, how are these so-called higher-order senses evaluated, and how are they used in sound design?

The discussion is getting complicated, so let's continue this another time. One thing I can say is that for some of the primary auditory sensations, physical characteristics can be extracted and are already being used as sound quality evaluation indices for sound evaluation and sound design. However, for higher-order sensory quantities, perceptions and evaluations differ depending on individual differences, situations, and contexts, so it is necessary to conduct subjective evaluation experiments after clearly defining the conditions. Physical quantities that correlate highly with the results of subjective evaluation experiments are often functions of various physical quantities, and it is necessary to clarify the relationships between them.

Yeah. It's a little difficult. Please explain it in simpler terms next time!