modulation audiogram?

Stevie Blunder sungstad at nospam_pcisys.net
Mon Dec 31 06:55:59 EST 2001


I personally find infrasound quite disturbing. Years
ago, when I was in the pro-sound business, it was
well known that ventilation noise is a big problem.
I also note that folks raised in a city are better
at ignoring infrasound.  I think 20 Hz is the limit
where we perceive sound as a continuous wave, and
begin sensing individual waves. Myself, and others
are quite sensitive to infrasound, but it may not be
our ears that we use to sense it. Infrasonic weapons
are based on the fact that various parts of the body
resonate at infrasonic frequencies.

My impression was that infrasound produces a
modulation of our perception like a audio system
that clips from a low frequency signal that is later
filtered out, leaving only the modulated higher
frequencies. Note how our hearing is impaired by a
pressure change, then consider doing that ~2-10
times a second.  Perhaps some people perceived the
affect as the same as external modulation. If so,
the presents of unmodulated pink noise should negate
the effect, since real infrasound would modulate
everything the individual hears.  I could infer
more, but enough for now.

In any case, the natural sources of infrasound are
all things to avoid, so we are programmed to get
very nervous when we sense it.

Steve Ungstad


Eckard Blumschein <blumschein at et.uni-magdeburg.de>
wrote in message
news:3BE24C2A.D4AC517A at et.uni-magdeburg.de...
> There are many complaints of single individuals
about disturbing
> low-frequency noise while sound level does not
even approach the
> admissible limit. Who can point such suffering
poeple to measurement
> that might be closer related to their perception,
maybe something like a
> modulation audiogram? I suggest a carrier of 100
Hz being 100% modulated
> with frequencies varying between 20 Hz and 1 Hz.
Some of the sufferings
> are pondering on whether or not to buy expensive
LF equipment in order
> to provide evidence for the existence of a real
hum. I guess, this
> cannot be recommended because the ear does not
physically resolve
> infrasound but the brain is very sensitive to
modulation in that region.
> So we rather need adequate audiometry based on
modulation, too. Don't
> we?
>
> http://iesk.et.uni-magdeburg.de/~blumsche/
>





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