Masking effect : the sound hidden in other sound

Hello, this is Mr.I of Shizuka Co., Ltd..

Today, I would like to introduce a mysterious phenomenon related to sound “masking effect”.
original article in Japanese (日本語の記事)

①What is “masking effect”?

Masking effect is a phenomenon in which one sound is drowned out and can not be heard when two sounds overlap.

Imagine a situation when you go to bed with your TV or air conditioner turned off. Is there any experience that the clock sound and the refrigerator sound came to bother you and could not fall to sleep? This phenomenon occurs because large sounds like television and air conditioners mask (hide) small sounds like the watch and refrigerator’s working sound, making it difficult to hear.

②Use for audio compression technology

This masking phenomenon is partly used for “audio compression technology” such as digital audio.

Please assume that you can not hear the sound “B” due to the masking effect of the sound “A”. In fact, both “A” and “B” sounds are present, but human ears only hear the sound of “A”. Therefore, by saving the sound of “B” that can not be heard, you can reduce the amount of information and save data capacity. This is voice compression technology. By compressing like this, it is possible to reduce the amount of data to a large extent without letting ordinary people feel deterioration of sound quality.

③Conditions under which masking effect is likely to occur

The conditions under which the masking effect is likely to occur are listed below. It is easy to occur when the sound is large, low, or when the frequencies of the two sounds are close.

・When the disturbance sound is large
・When the interference sound is low frequency
・If the frequency band of the disturbing sound is close to the frequency band of the disturbed sound

④Noise control and masking effect

Masking effect also affects noise control measures.

For example, when there are two or more machines that become noise sources, such as factories. Suppose a case when you succeeded in reducing the sound as a result of soundproofing the machine that has the largest sound. However, there are times when the sound of the machine that has the second largest sound comes to mind. There is a possibility that sounds that you do not normally mind usually emerge due to the masking effect. Therefore, it is necessary to know where, what kind of sounds, how many sounds exist, and when there are soundproofing measures.