From: Syd Curtis <>
> For getting hearing aids one listens for threshold amplitudes at specific
> frequencies over the normal hearing range, and the hearing aid is designed
> according to the results. I surmise that even with those with apparently
> normal hearing there can be differences in hearing sensitivity at various
> frequencies. If so, surely two people listening to the same sound at the
> same time, may hear it differently.
During 2 1/2 of my years in the Army one of my daily duties was to do
large numbers of hearing tests. For such work we had a semi-automated
testing system and the subjects were in small individual soundproof
rooms. We did test in individual frequency bands, one ear at a time. The
results of those tests, on mostly male late teens, early 20's, were all
over the map. It was extremely rare for anyone to have the same
sensitivity in every band. Even those with excellent hearing would have
some falloff at the higher frequencies, and we were only testing to
8khz. Differences of 30-40db across the bands were common. The 100 dB
range we tested was not often reached in the differences as most with
bad hearing in some bands would not reach to most sensitive end in any
band. We tested from -10dB to 90dB. In those days I came very close to a
perfect -10dB across the board, but not quite.
Those Army tests were intended only to screen new recruits. We rejected
for service those with too low a hearing level. They used many fewer
bands and tests than are used to prescribe a hearing aid.
Yes, in actual hearing sensitivity we each hear sounds differently.
> Walter takes a sound, manipulates it with computer technology, and posts the
> results on a web site. This is sent, digitally, I assume, via satellite
> technology, around the world then down Vicki's phone-line to her iMac, which
> converts digital to analogue, and the analogue signal is interpreted by some
> sound-producing device which vibrates the air, eventually causing pressure
> variations in Vicki's ear-hole.
>
> Ditto, with other naturerecordists.
>
> To me, Mozart sounds better than Messiaen.
>
> I'd be surprised if everyone did agree on which samples sound the best!
On top of the pure mechanics of hearing and our individual sensitivities
there is how we interpret sound. As I've pointed out our brains
interpret the signals from our ears according to what we have heard,
what we think about the sound, our current emotions and so on. We filter
what our own ears picked up even before becoming aware of the sound.
Walt
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