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In Reply to: Re: Some morsels posted by Middleground on November 13, 2002 at 07:58:58:
The question isn't "if it's there, can we perceive it?"The link below is to a paper showing that sound at frequencies above 20 kHz does cause brain activity in areas outside the auditory cortex. In other words it shows that the brain responds in some way, even though we don't "hear" the sound since it is above the upper limit for hearing. There is no doubt, on the basis of the brain scans taken for this research that we do perceive the sound in some way.
The question is what kind of effect that perception has - does it influence our interpretation and appreciation of the sound, or modify our enjoyment of music in some way. If it does, we probably want audio systems that can reproduce all of the frequencies created by musical instruments and probably some way above that given the existence of sum and difference tones, unless we can find an upper limit to the frequencies the brain responds to. If it doesn't influence our appreciation of the music it isn't an issue.
I think the jury is still out but I wouldn't be surprised to discover that we need wider bandwidth.
David Aiken
Follow Ups:
There is another aspect to this. It is quite possible that the audible effects of the ultrasonic signals were due to intermodulation effects which were in the audible range.This was the conclusion of Ashihara Kaoru and Kiryu Shogu in AES Convention Paper 5401 presented at the 100th Convention may 12-15, 2001. In other words, when they played the signals over the same loudspeaker, people could hear the difference, but when the signals in the audible range and the ultrasonic range were played over separate drivers, they could not.
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"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
The evidence offered was PET scans showing brain activity in areas not involved when listening to music with no ultrasonic content. I can't see why intermodulation products in the audible range should excite such activity when normal musical content in the same range didn't.It seems reasonable to me for the researchers to assume that a different part of the brain is responding to the ultrasonic frequencies given the results. There could be all sorts of reasons for that amd it doesn't contradict the paper you referred to which was about heard differences rather than about perception in a non-auditory area of the brain.
More work required by both research teams?
More work is always needed. Spectral analysis showed the intermodulation effects, and DBTs showed they were audible. Whether that can be correlated with the brain scans is another matter, but we'll never know unless the intermodulation effects are eliminated. As I said, the effects may be due to intermodulation effects, and we can hardly know otherwise until the tests are done under conditions where they do not occur. I don't think we disagree here.
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
It would be interesting to find that the ultrasonic signals coupled into the EEG and/or PET system, giving false results. I've seen worse.It'll also be interesting to see the peer review/reproducibility on that one.
have an effect the PET system. It is just a fancy geiger counter :-) I do not know about the EEG, that is way outside of my field of expertise,I think both could be easyly verified by taking measurements without the subjects present and with and without US fields.
BTW i like this study because it does not rely on what the subjects percieve, but rather on what stimuli their brain reacts to.
Pet is "Positron Emmision Tomography. But it has a 2mm accuracy, as that is the average distance a gamma ray travels before impact and emission of positron; giving a rather fuzzy picture of brain activity with respect to tagged molecules. Or is it the other way around... So confusing..Now, EEG, "electro"... there's a measurement that an EE can handle...
Actually, they do PET stuff here. I give tours to the college students and professors occasionally, and sometimes I actually learn about it.
But, what scares me is the fact that the medical people who do the research have no idea how the systems interact, and sometimes that can bias the results.
John,I do medical imaging software for living, so PET is one of the areas that i had to struggle with for a number of years :-). In any case the verification of the measurement accuracy is quite simple, as i mentioned in the previous post. Whether they actually calibrated their measurement is not clear from the article, i hope they did. (Nobody wants to be in the cold fusion vs. red cooler discussion.) I would love to see independent verification of their results since they do go against the grain of conventional wisdom. Better way of measuring this would be using functional MR (Magentic Resonance). The effect of HF sound field on the pick up coils would need to be studied more carefully, i suspect an open MR would be more susceptible to interference. I do not see how you could do this with a traditional small bore MR.
This one intrigues me because it could account for part of the difference between CD and vinyl.I run a CD only rig these days and have for over 10 years now, and I don't think CD sounds as bad as its worst detractors claim. I haven't had a chance to do an AB of the same music on CD and vinyl with a good rig and I rarely get a chance to listen to vinyl these days and I'm intrigued, especially since I had something like a minor stroke in 1983 and ended up with some minor sensory deficits which don't include any hearing issues, at least on normal hearing tests. CAT and MRI scans don't show anything but the sort of problems I have could occur with damage too small to show, and the view is that the damage is in the left thalamus which is one of the areas implicated for response to frequencies above 20 kHz in this study.
I wonder what a PET scan of my brain would show, but I don't know anyone who could do one and the cost for getting that done as a matter of interest rather than medical need (health insurance wouldn't cover it) is more than I'd want to spend for the sheer interest of finding out. On the other hand, if someone wants to run a study to try and replicate the results and they want to run it in Brisbane in Australia, and they're looking for subjects, I am available.
I once ran a comparison between CD and vinyl. Same song.Vinyl disappointed me. For one reason. On one song, there was ONE bass note missing from the vinyl. Only one!!!! Lowest one in the song, only used once by bass guitarist. Apparently they (recording studio) decreed that the groove excursion was high enough, and removed it!!! And to top it off, my vinyl was a 12 inch single. Only one song, 6 minutes, on one side. Modulated all to "heck".
I miss vinyl..and tubes. and klipsh horns. Oh well.
Oh yes, my system at the time was not really a sit down and listen system, just a bass KICK A## (1200 watts) system. So, any realism in the reproduction just weren't happening.
If you've played with tubes and vinyl then you're one of us. Klipsh might be a little "iffy", but, hell, they've got horns so I guess that's close enough.Anyone who would put 1200 watts to driving a pair of Kliphs is certainly crazy enough to qualify as a true audiophile.
Gave them up, though. For mobile use, they were too cranky with respect to placement, and too heavy. But boy, the sound....
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