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Human hearing

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Posted on November 12, 2002 at 07:35:03
middleground
 I believe that it would be a fundamental question to attempt to settle at the outset, since it appears that many audiophiles are still hard at work convincing themselves that humans (or is that just Golden Eared Humans) can hear beyond anything that science has for a good while now accepted as the limits of human hearing. The upper frequency extreme seems to be what is subject to question by some. That a circuit has to go beyond 20Khz to maintain linearity and all manner of other good things in the range humans can actually hear is not the debate really. As somewhat of a sidebar to this question, it would seem that the question of pure tones vs. harmonics will enter the picture. I presume that if a subject or a number of subjects cannot hear a pure tone at a given high frequency, it would be well nigh impossible to hear it as some harmonic of some other tone lower down the scale. Basically what I am getting at with this somewhat garbled last sentence, is this notion among audiophiles that somehow even if the pure tone can't be heard, magically, it can be if associated with other tones that can be heard.

 

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Some morsels, posted on November 12, 2002 at 09:23:41
Penguin
Audiophile

Posts: 7116
Location: Delaware
Joined: August 5, 2001
 How it effeects hearing ? Who knows. BTW i have posted this before on AA.

 

Re: Human hearing, posted on November 12, 2002 at 09:56:37
jk
Audiophile

Posts: 366
Joined: October 4, 1999
 This topic has always been close to my heart. I'll never forget the time when at the age of about 12, I was in the Smithsonian and they had the moon rocks (circa 1972) on display. I could hear the burglar alarm (it was more painful than anything else) as you got close to it, no one else could hear it. It was an sound so high pitched I can't even describe it. I'm 43 now, doubt I can hear anything like that - I wish two things: 1) I had measured how high I could hear back then (burgular alarms, dog whistles, TV's) 2) I hadn't listened to such loud music at times over the years. (I remember how proud I was that my ears rang for 2 days straight after seeing some stupid band - oh well we all get smarter)

I can still hear dog whistles, what frequency do you think that would typically be at? BTW - I wouldn't describe it as a pleasant tone, it is bordering on painful. I met with a gentleman who had his MD and specialized in the ear. He wouldn't buy it, he explained to me that the mechanics of the human ear make it literally impossible to vibrate (and therefore hear) at frequencies much above 20K HZ. On the other hand, I saw an interesting show on ultrasonic experiments. The scientists verified that a 30Khz signal was present at the transducer by mechanically coupling their teeth/jaw to the transducer - they just used a rod of wood (or metal? I forget). They placed the rod on the transducer, then bent down and put their tooth on the end of the rod. When the skull vibrated it was perceived as sound. Interesting isn't it?

 

Re: Some morsels, posted on November 12, 2002 at 10:43:15
middleground
 Thanks. Glanced at the article. Interesting, but seems to be focusing on the fact that known musical instruments have harmonics above 20Khz, which no one doubts. What I find less tantalizing is the fact that, based on very little that is substantive, the author concludes that because they are there somehow we must hear them. Strange. Kind of like saying because Pluto is there we can see it with the naked eye. Correct me if I am wrong. The author then goes on to mention some heretofore unknown mechanism whereby humans perceive these frequencies trough something other than the ear itself. Very little to support what he is saying. On one of these experiments, the author indicates that he got only partial results which have to do with EEGs monitoring brain activity all the while the subjects claim to hear nothing. The other source dealt with profoundly hearing impaired people. I am not certain that adding to the mix by delving into research on hearing pathologies qualifies as supporting that normal hearing goes beyond 20Khz. Then again, I am not an expert or scientist and wish that those more qualified than me provide their input. Good day.

 

Re: Human hearing, posted on November 12, 2002 at 11:13:21
centurymantra
Audiophile

Posts: 284
Joined: October 30, 2000
 I have encountered some interesting discussions and writings regarding the significance (or lack thereof) of frequencies in the upper registers above 20khz. There seems to be some sound evidence (no pun intended) and arguments to support the idea that the registers that are above the established audible levels do inform the frequencies, harmonics, etc. below and assist in shaping subliminal cues, spatial information, etc. I cannot, unfortunately, refer to specific facts or link to any of these areas of discussion but I do recall being very intrigued by the ideas that were being presented. I know that some people were engaging in studies of the effect that frequencies and sounds generated by computer monitors, power supplies, etc. may have on people who work at or near computers for long periods of time. Apparently, they have measured the decibel levels of frequencies in the upper ranges around some computer systems to exceed 90db. It seems to me that, even if these sounds are not being 'heard', they are entering our nervous system in some fashion and interacting with our body and mind on some level.

Bryan K.,
Music Lover & President-elect of C.C.A.C. (Concerned Citizens Against Cilantro)

 

Sum and difference signals, posted on November 12, 2002 at 11:20:01
Duke
Dealer

Posts: 4429
Location: Princeton, Texas
Joined: March 31, 2000
 Let's say you have two coincident pure sine wave tones generated simultaneously - a 30,000 Hz signal and a 31,000 Hz signal. There will actually be four tones produced - the original two, plus (at greatly reduced volume) a tone that is the sum of the two (30,000 Hz + 31,000 Hz = 61,000 Hz), plus (at greatly reduced volume) a tone that is the difference of the two (21,000 Hz - 20,000 Hz = 1000 Hz). That difference signal is called a "beat".

This is at least one way in which harmonics above the normal frequency range of human hearing can affect the audible range.

Whether or not this translates into a requirement for playback systems with response well in to the ultrasonic range I cannot say. Theoretically the audible beat frequencies would have been captured in the original recording, and so would not have to be re-created by the physical interaction of ultrasonic frequencies. Personally I think bandwidth well into the ultrasonic range is desirable, but probably not cost-effective to pursue.

Below is a link to a site that explains beats much better than I did.

 

Re: Some morsels, posted on November 12, 2002 at 11:22:39
John Escallier
Audiophile

Posts: 4425
Location: Long Island
Joined: October 3, 2002
 ##Correct me if I am wrong##

Ok. But say something wrong first.

##wish that those more qualified than me provide their input.##

Can't help you there.

Your comments are right on.

TTFN, John

 

Re: Sum and difference signals, posted on November 12, 2002 at 18:50:28
Hafdef
Audiophile

Posts: 339
Joined: November 21, 2001
 futher to what I did not find in the article, these beat frequencies are not heard as the summed difference tone but are sensed as warbling beats as the phase relationships becomes constructive and destructive.
As such any reinforcement of the fundamental through beat frequecies appears to be a function of our ability to process phase information very accutely. Also, beat frequencies can be derived from tone produced from different instruments such as a 440hz tone on a piano and a 450hz tone from a quitar. The beat frequency is sensed as a warbling 10 beats per second. I understand if 440 hz is played in one ear and 450 hz in the other the brain will create a 10 hz tone, this is called a binaural beat. It is interesting the brain can create the fundamental of a tones 44th and 45th harmonic and do so through phase relationships.

It is theorized by some our ability to process extremely complex phase information is largely responsible for sound location detection. This can be taken a step further to help describe the importance of omnidirectional bass frequencies and proper phase relationships contibution to sense of space from out audio systems.

A production of a 32 hz tone will produce a harmonic structure of 64, 96, 128, 160 etc. The amplitude relationships of the fundamental and harmonics will create it's own unique set of phase beat frequencies for a given space which our brains interpret as that space. Now if we record that tone and play it back through our audio system what happens to the original amplitude and phase relationships? Our own listening room resonant frequencies will change the amplitude relationships and the electronics will do the same to amplitude and phase relationships. On top of this our brains are forced to do double spacial duty by not only interpreting the space of the recording but also interpret the low frequency information to give us a sense of our own listening room spacial information.

I'm writing off the top of my head here in somewhat unchartered waters for me so don't know if this is correct or not but it sure explains why producing low frequencies properly (for what they are naturally for) is deemed so damned difficult and expensive.

Anyone here in the know about this stuff?

 

Re: Some morsels, posted on November 12, 2002 at 20:48:30
Hafdef
Audiophile

Posts: 339
Joined: November 21, 2001
 "Kind of like saying because Pluto is there we can see it with the naked eye"

Interesting analogy, because Pluto can not be seen with our eyes does this mean it has no influence on us? Pluto was discovered because the other planets had a slight perturbation in their orbits therefore it was believed the gravitational pull of an unknown planet caused this.

Eventhough we can not see the planet it does exist and by gravitation forces influence our planet and therefore us. Similarily, just because we can't hear something in the traditional sense doesn't preclude these frequencies from having other influence on us or the sounds within our hearing range.

 

Re: Some morsels, posted on November 13, 2002 at 07:58:58
middleground
 Wow! I really believed that this basic question would be easy enough to solve, to lay some kind of groundwork for further inquiries and discussions. Now, we have this sort of butterfly-fluttering-its-wings-in-China-having-an-effect-on-weather-in-New-York-type-proposition. The issue here is whether admitting that some phenomena does exists, does it assuredly imply that we as humans can perceive it. This is the bread and butter of subjectivists. Take some pretty well established phenomena, for example let's say the skin effect, and then contend that because it exists, it, therefore, is heard by the human ear at the end of the reproduction chain. Now we have some sort of an outline of an argument that audio reproduction entails more than the human hearing mechanism. I don't know if any discussion with any kind of basis in science can ever get off the ground if things as fundamental as these can't be settled. Audio in the last fifteen to twenty years really seems to be best summed up as a paradigm lost.

 

20khz sine vs. square, posted on November 13, 2002 at 09:52:54
kvk
Audiophile

Posts: 155
Joined: June 27, 2002
 Assuming you can hear to 20khz, would you be able to hear the difference between a 20khz sine wave and a 20khz square wave after compensating for the difference in energy?

I don't know the answer to that question but if it is "yes", I think equipment would have to extend beyond 20khz to get true sound reproduction.

 

No…, posted on November 13, 2002 at 12:00:51
David Aiken
Audiophile

Posts: 5858
Location: Brisbane
Joined: September 25, 1999
 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

 

Re: No…, posted on November 13, 2002 at 19:14:00
John Escallier
Audiophile

Posts: 4425
Location: Long Island
Joined: October 3, 2002
 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.

TTFN, John

 

Re: No…, posted on November 13, 2002 at 22:37:51
David Aiken
Audiophile

Posts: 5858
Location: Brisbane
Joined: September 25, 1999
 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.

David Aiken

 

I did that, posted on November 14, 2002 at 15:27:44
John Escallier
Audiophile

Posts: 4425
Location: Long Island
Joined: October 3, 2002
 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.

TTFN, John

 

Re: Human hearing, posted on November 14, 2002 at 15:48:21
John Escallier
Audiophile

Posts: 4425
Location: Long Island
Joined: October 3, 2002
 ##The scientists verified that a 30Khz signal was present at the transducer by mechanically coupling their teeth/jaw to the transducer - they just used a rod of wood (or metal? I forget). They placed the rod on the transducer, then bent down and put their tooth on the end of the rod. When the skull vibrated it was perceived as sound. Interesting isn't it?##

They probably use the coefficient of friction to verify signal presence.

 

I doubt that US would.., posted on November 14, 2002 at 16:10:55
Penguin
Audiophile

Posts: 7116
Location: Delaware
Joined: August 5, 2001
 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.

dee
;-D

 

Alas, if it were only so easy.., posted on November 14, 2002 at 18:41:26
John Escallier
Audiophile

Posts: 4425
Location: Long Island
Joined: October 3, 2002
 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.

TTFN, John

 

Hey man, posted on November 15, 2002 at 00:34:24
Phil Tower
 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.

 

Agree..`, posted on November 15, 2002 at 06:14:10
Penguin
Audiophile

Posts: 7116
Location: Delaware
Joined: August 5, 2001
 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.


dee
;-D

 

Re: No…, posted on November 17, 2002 at 08:27:35
Pat D
Audiophile

Posts: 12506
Location: Fredericton NB
Joined: June 20, 2000
 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.
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)

 

I'm dubious about that possibility, posted on November 17, 2002 at 23:25:48
David Aiken
Audiophile

Posts: 5858
Location: Brisbane
Joined: September 25, 1999
 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?

David Aiken

 

Re: I'm dubious about that possibility, posted on November 18, 2002 at 06:45:16
Pat D
Audiophile

Posts: 12506
Location: Fredericton NB
Joined: June 20, 2000
 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)

 

They were Klipsh corner horns., posted on November 18, 2002 at 15:33:07
John Escallier
Audiophile

Posts: 4425
Location: Long Island
Joined: October 3, 2002
 Gave them up, though. For mobile use, they were too cranky with respect to placement, and too heavy. But boy, the sound....

TTFN, John

 

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