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Ken:
The other day, you mentioned one of the ability of a man
to listen to voice, or some party phenomenon in a talk
about harmonic overtone.
Dad:
Oh, you mean cocktail party phenomenon?
Ken:
Yes. But what is cocktail party?
Dad:
It is a buffet-style party with drinks and
snacks. In a party, it is very noisy with conversation
and background music mixed. Even in such an environment,
you can listen to conversation partner or what you are
interested in though it is a little distance away. This
is how it was named. It is a work of human acoustic
sense with which you pick up a certain source of sound
out of multiple overlapped sources.
Ken:
You mean though it is noisy around, you can catch what
you want if you attention to, dont you? In a break time
when classmates are messing around, I can catch what a
guy says if I hear my name guessing hes talking about
me. You can listen with a help of awareness.
Dad:
You can not listen if the sound volume of what you want
is too small compared to noise level around, not to
mention. But as you said, you can listen with care.
Ken:
Is there anything relative to harmonic overtone you told
the other day?
Dad:
Listen carefully as this is a bit difficult. It is rare
that only one factor of harmonic overtone is emphasized
out of complex sound discharged from one source in
nature. This means that if there is an emphasized
harmonic overtone, there is another source of sound. So
a man recognizes it a sound out of another source
separately.
Ken: Then, can a man
tell there are ten kinds of source of sound when ten classmates are
talking?
 Dad:
I doubt it in such a case with many people.
It has been found that distinguishing sound by each
source of sound is processed in a brain which controls
acoustic sense connected to inner ear through auditory
nerve.
Ken: Inner ear has a
function to analyze tone of sound, doesnt it? The innermost brain
distinguishes source of sound, right?
Dad: Yes. A process
to reintegrate by source of sound is named auditory scene analysis by
a researcher named Plegman. Sounds from the same source has common
characteristics not only that harmonic overtone is common but also that
they start and stop ringing at the same time, the change of
characteristics of direction from which frequency and sound comes occurs
at the same time and its changes are very slow.
Ken: It sounds
difficult. The direction of sound has something to do with it.
Dad: It is impossible
to replay the direction if it is recorded with one microphone alone. So
it is difficult to distinguish source of sound.
Ken: How wonderful
the acoustic sense of a human being is! Is it possible to recognize
source of sound by recording sound and analyzing with computer?
Dad:
Voice-recognition technology seems to have been advanced. It may not be
impossible for a computer to distinguish sounds ringing at the same time
if an ability of human awareness is engineered for application. What
made a man obtain this kind of ability is a function which vertebrate
animals have developed to survive running away from bigger animals and
hunting smaller ones.
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