cocktail party phenomenon
Oto-kun
The other day, my father mentioned in his talk about harmonics that there is a phenomenon related to the ability of humans to hear sounds, called something like the party phenomenon.
father
Ah, it's the cocktail party phenomenon.
Oto-kun
What is a cocktail party?
father
"It's a standing party with drinks and light snacks. The party venue is usually noisy, with voices and music mixing together. Even in such an environment, you can hear the voice of the person you're conversing with, or pick up on things that interest you from a distance if you pay attention. This is where the name comes from. It refers to the human auditory ability to selectively extract specific sound sources from multiple overlapping audio sources."
Oto-kun
Even if the surrounding noise is loud, does it mean that if you focus, you can distinguish only the sounds you want to hear? Speaking of which, during break time, even when everyone in class is noisy, there are times when I can hear my name and think that they are talking about me, and I can understand the content of the conversation. It shows that the power of attention allows us to listen.
father
"Of course, if the level of the sound you want to hear is too low compared to the surrounding noise level, you won't be able to hear it. However, as Oto says, it becomes possible to hear it through the power of attention."
Oto-kun
And what is the relationship with the harmonics you mentioned the other day?
father
It may be a bit difficult to discuss, but is that okay? In the natural world, it is rare for only one overtone component to be emphasized among the complex sounds emitted from a single sound source. This means that if an overtone is emphasized, it would suggest that there is another sound source. Therefore, humans separate and interpret it as a sound coming from a different source.
Oto-kun
So, does that mean that when 10 people are chatting in a class, humans can distinguish between 10 different sound sources?
father
I wonder if that's too much. Research has shown that distinguishing between different sound sources is processed in the brain, which is connected to the inner ear through the auditory nerve.
Oto-kun
The inner ear you explained before has the function of analyzing the pitch of sounds, right? It means that the brain further distinguishes the sound sources.
father
I see. It seems that a researcher named Pregman called the process of reintegrating sounds from different sources auditory scene analysis. It has been found that, in addition to the commonality of overtones as a characteristic of sounds emitted from the same source, they also start and end simultaneously, and changes in frequency and the direction from which the sound arrives occur similarly, with gradual changes.
Oto-kun
It's somehow difficult, isn't it? The direction of the sound is also related, isn't it?
father
When recording sound with a single microphone, it becomes difficult to separate sound sources because it cannot reproduce directional sound.
Oto-kun
Human hearing is amazing, isn't it? I wonder if it's possible to distinguish sound sources even after recording the sound and analyzing it with a computer.
father
It seems that voice recognition technology is improving, but if we could apply the power of human attention in an engineering context, it might not be a dream for computers to distinguish sounds occurring simultaneously. It is believed that humans possess such abilities as a function developed in vertebrates to escape from large animals and survive by eating smaller creatures.