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This topic comprises 4 pages: 1 2 3 4
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Author
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Topic: Help! My onscreen image looks too good!
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 08-22-2009 10:00 PM
Now I don't know what to think. I wonder why 3 dB stuck in my head. Several subject-matter experts referred me to Moore, but I'm not sure how to interpret him.
See Moore, Brian C. J. An Introduction to the psychology of hearing, 5th Edition. Emerald Group Publishing, 2003. ISBN 0125056281. pp. 138-139, available on Google Books:
quote: Moore
For wideband noise, or bandpass-filtered noise, the smallest detectable intensity change is approximately a constant fraction of the intensity of the stimulus. In other words, ΔI/I is roughly constant. This is an example of Weber's law, which states that the smallest detectable change in a stimulus is proportional to the magnitude of that stimulus. The value of ΔI/I is called the Weber fraction. If the smallest detectable change is expressed as the change in level in decibels, i.e., as ΔL, then this too is constant, regardless of absolute level, and for wideband noise it has a value of about 0.5-1 dB. This holds from about 20 dB above threshold to 100 dB above threshold (Miller, 1947). The value of ΔL increases for sound which are close to the threshold.
Though a smart person points out to me that this is dB of intensity, not dB of SPL, so it must be multiplied by 2, giving us 1-2dB.
Note that this is for wideband noise. He goes on to say that it improves at high volumes for pure tones.
On the other hand, the end-of-chapter summary on p. 158 says,
"We are able to detect relatively small changes in sound level (0.3-2dB) for a wide range of levels and for many types of stimuli." and assuming that's intensity, that suggests 0.6-4 dB of SPL for types of sounds more general than noise and pure tones.
YMMV ![[Smile]](smile.gif)
--jhawk
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Martin Brooks
Jedi Master Film Handler
Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002
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posted 08-28-2009 07:00 PM
quote: Bill Enos
I have a friend who claims to be able to hear beyond 30KC and refuses to use hearing protection in extremely loud situations because he can, at will, tighten his ear drums and thus avoid hearing damage.
I doubt that very much, but it's easy enough to test whether he can hear to 30KHz. If he CAN hear to 30KHz, I'd like some of his DNA so it can be combined with mine or an ear transplant with him or something.
And I don't know what he means by "tightening his eardrums", but what loud noise does is destroy the hairs that are in the cochlea. Pressure waves cause the liquid in the cochlea to move hairs which in turn simulate the auditory nerve. Exposure to loud noises causes the hair cells to become less sensitive. Unfortunately, these hair cells do not regenerate or heal - once damaged, that's it. Unless he has some unique bone or membrane structure that he can squeeze together to block loud waves from reaching the eardrum, I don't see how he can protect his ears without an artificial device.
I read a story online about how some merchants who don't want teens and kids hanging around their stores have a device that puts out a high frequency. It drives the kids nuts, but adults can't hear it (although due to iPods and loud rock concerts, there is now substantial hearing loss among the young as well - I've read estimates that say 15% of young people have some hearing loss.) My daughter once walked into a house (she was in her 20s at the time) where they had one of those high-frequency bug eliminators and it drove her nuts - she had to leave. I didn't hear a thing.
I doubt whether any person over 35 on this Forum can hear anything much past 18KHz, especially those living in cities. I keep praying that in my lifetime, they'll figure out how to repair or heal high frequency hearing loss. I would love to get my teen-aged hearing back.
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