Anthony Lalande wrote...
>While I'm not sure what exactly AGC means, I have heard somewhere
>that ears are able to focus and lose focus of sounds and noise in a
>dynamic way. I was once advised to buy full-ear headphones as
>opposed to ear-buds because sounds hitting the outer part of the ear
>actually help the inside of the ear adjust to what it's listening
>to, and can help prevent damage in a way that ear-buds cannot.
>
>Does anyone know enough about the working of the human ear to
>validate or deny this?
This sounds like rubbish to me. The tympanic membrane (ear drum) is
linked to the ossicular chain (hammer, anvil and stirrup in plain
English) and they convert sound energy into mechanical energy before
it gets passed to the cochlear in the inner ear to be converted into
electrical signals which are processed by the brain.
The shape of outer ear (ie the bits stuck to the side of your head)
is good for capturing sound and directing it down the ear canal,
which acts as a resonating chamber, but the ear itself cannot simply
'adjust' to the sound that 'hits' it. Remember, the pupil of the eye
can contract and expand to allow in less / more light, but there is
no equivalent function in the ear. If the amplitude of the sound goes
above the loudness discomfort level (LDL) for a period of time you
may suffer temporary or even permanent hearing loss. This can
occur in many ways, commonly in the form of hairline cracks in the
tympanic membrane; or hair cells in the cochlear which carry on
'firing' without stimulus (usually resulting in tinnitus).
Meanwhile, its the brain's job to process the electrical signals fed
to it by the inner ear. Although the cochlear does do an
astonishingly complex job, the brain, *not* the ear does the
processing, and as I've already written, the ear can't really adjust
itself (only *you* can, by putting your hands over your ears)
Oh yes, AGC is Automatic Gain Control. This is a technique used on
some MiniDisc recorders and hearing aids as a way of 'squashing'
peaks in the sound being recorded / processed. However, it is a
relatively coarse method of control, and the use of AGC on hearing
aids can lead to much distortion of speech.
Of course, all this isn't to say that you can't damage your hearing
with earbuds. They provide less isolation than full-ear headphones,
which makes it tempting to increase the volume in order to overcome
extraneous noise. So yes, earbuds may indeed be (potentially) worse
for the health of your ears, but not for the reasons you were
told. Hope that answers everything.
Robin.
----------------------------
Robin Landy
Manchester University
[EMAIL PROTECTED]
Mobile: 07968 775304
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