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December 16, 2007, 12:15:33 PM
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Topic: sound: reception vs perception  (Read 568 times)
« on: September 24, 2007, 10:09:38 PM »
AndyH Offline
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While this mainly relates to the Sound Therapy material, is isn't in regard to views about whether or not that music has the beneficial effects claimed. It is about the physics of sound reaching and effecting the ear. For purposes of being able to consider the question of interest, please let us make the assumption that listening to this modified music can provide the results claimed for it.

This particular approach to sound therapy is all about being mobile so that the therapy can be undertaken frequently, for extended periods, causing little interference with other activities.

Instructions say

** The "proper" use of the material is at low volume, with open headphones. One should be able to carry on a conversation, watch a movie, do almost anything, without the (treated) music getting in the way. There is no need to pay attention to the music at all. It is, apparently, the physical effects on the ‘organs of hearing' that are important, not any mental evaluation of what one hears.  If one can't readily hear whatever else one needs to hear, the music is being played too loudly.

** One should set the volume in a reasonably quiet environment, such as at home. When going anywhere else, leave the volume setting unchanged, regardless of how noisy the new environment may be.

The instructions about not changing the volume setting to match conditions make sense to some extent but are not exactly intuitively obvious. In regard to many uses of sound, such as carrying on a conversation, we must raise the volume when in a noisy environment if we hope our activity will have any result.

In reality, after setting an appropriately low volume for the therapy music playback, taking it into a moving automobile can make it pretty much unhearable. It seems reasonable that the energy output of the headphones is not changed, but the sound is so masked by noise that perception may be completely lacking. We are unable to hear the music no matter how much we pay attention; the higher level noise masks the music.

The question is about sound energy reaching the parts of the body involved in hearing when we are in a noisy environment, at least those parts of the body involved when we are not in a noisy environment. Possibly bone conduction of the music is not a significant factor under these low energy level conditions, regardless of other noises present.

How much of our being unable to distinguish the music in the total sound coming into our ears is in the way the ear responds and how much of it is due to the music energy itself being modified through modulation, dampening, or any other interaction with the noise?

Another way to possibly examine this is to make a microphone recording of the music played at a very low volume in the presence of high level background noise. Assume the noise has a constant enough character to be reasonably profiled by NR software. We can't hear the music in the raw recording, just as we could not hear it first hand. Can NR recover the music? Consider only near field, not worrying about any characteristics imparted by a real world listening space (i.e. we don't care if NR kills the ambience). I know NR can often recover low level LP recordings, such as fade-in and fade-out, when they are virtually unhearable without NR, but I'm not sure if mixing in the air of the real world is quite the same thing.

One purpose of the question is an evaluation of whether or not playing this music at a very low volume in a noisy environment really has any chance of being beneficial -- making the assumption that it is beneficial, as claimed, in a non-noisy environment. Is it possible that the music has its ‘normal' effects on the various parts of the ear at the same time that the noise has its own effects?
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Reply #1
« on: September 24, 2007, 11:12:41 PM »
SteveG Offline
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Well, I think the whole thing's extremely dubious anyway - but if you want some real numbers relating to the way that the ear protects its inner organs against external noise, which is partly what the malleus, incus and stapes are for - (they are not just for transferring sound from the eardrum to the inner ear), then you have to consider what they do - which is to provide a sort-of 'step-up' transformer effect that compensates for the large impedance mismatch between air and the fluids of the inner ear. This causes a loss of about 30dB, which is what the step-up compensates for.

As part of the mechanism, there are two small muscles that can operate on the step-up and reduce its efficiency. That's why there are three bones - this enables it to be a variable step-up rather than fixed ratio that in theory you could implement with just one bone. The muscles operate on the eardrum itself and the stapes; the mechanism is autonomous and it kicks in 10ms after a stimulus of 90dB above the usual 0dB acoustic reference - as long as it lasts more than 10ms. And this mechanism is pretty good - it can reduce that 30dB gain to about 2dB.

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Is it possible that the music has its ‘normal' effects on the various parts of the ear at the same time that the noise has its own effects?

The mechanism is truly autonomic - it can't tell the difference between music and noise, which is why I referred above to a 'stimulus'.

Most of what you read about this sort of technique is mumbo-jumbo. It's not about the physical effects of sound on the ear, because none of the people who write this stuff have the slightest idea of how ears work, as a rule. They are more interested in selling you something, and sometimes they manage to disguise this in pretty clever ways.
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Reply #2
« on: September 26, 2007, 07:51:58 AM »
MarkT Offline
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I would be (marginally) prepared to believe that "adjusted" music could have some beneficial effects in some closely defined circumstances (have I covered my ass enough dya think?), but the noisy background scenario sounds a little too much like the claims for homeopathy,
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The concept of the memory of water goes back to 1988 when the late Professor Jacques Benveniste published, in the international scientific journal Nature, claims that extremely high ‘ultramolecular’ dilutions of an antibody had effects in the human basophil degranulation test, a laboratory model of immune response. In other words, the water diluent ‘remembered’ the antibody long after it was gone. His findings were subsequently denounced as ‘pseudoscience’ and yet, despite the negative impact this had at the time, the idea has not gone away
It seems to be a low level sound in a high level noise environment would suffer the somewhat same fate as the diluted antibody
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"Having most of the universe in a form of matter you can't see is fairly embarrassing"

Steven Phillips, professor of astronomy at the University of Bristol
Reply #3
« on: September 26, 2007, 08:53:16 AM »
SteveG Offline
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It seems to be a low level sound in a high level noise environment would suffer the somewhat same fate as the diluted antibody.

If you have coherent, correlated audio present in decorrelated noise, you can extract it - this is the basis that dither works on. But that doesn't affect the way that the ear's autonomous response to that noise happens. If there's enough noise present, then the wanted sound will be attenuated by up to about 28dB. And since that wanted sound was at a pretty low level anyway, I'd say that we were certainly drifting into homeopathic (placebo?) remedies territory here...
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Reply #4
« on: September 26, 2007, 11:15:52 AM »
MarkT Offline
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I'd say that we were certainly drifting into homeopathic (placebo?) remedies territory here...

Yeah, placebo is probably the best you could hope for.
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"Having most of the universe in a form of matter you can't see is fairly embarrassing"

Steven Phillips, professor of astronomy at the University of Bristol
Reply #5
« on: September 26, 2007, 09:48:30 PM »
AndyH Offline
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So, it would seem then that the physical effects on the hearing mechanisms of this low level audio, whatever those effects may be, are possibly modified but little by environmental noise, as long as the total level reaching the eardrum does not exceed 90dB. At higher levels of environmental noise the signal will be attenuated by 28dB, so its efficacy almost certainly has to be greatly diminished. A reasonable summary?

I'm guessing the 0dB in this consideration is the threshold of hearing. Some particular amount of sound energy in the air equates to this 0dB, no? Is that only at a certain frequency, perhaps in that part of the audio spectrum where human hearing is most sensitive? Is it not the case that the sound pressure level must be higher to be heard at all in other parts of the audio spectrum?

Is the 90dB increases that trips the defense mechanism at a particular frequency? Will a frequency restricted sound, such as a loud 18kHz tone, produce the same result?

Something seems wrong with the description of this mechanism. If the sound level is at 89dB, we have a certain experience of its loudness and a certain ability to differentiate different components (assuming the total sound is a mixture of inputs, not one constant isolated tone).

Now increase the loudness by 2dB to 91dB. 2dB is often noticeable but not as a very big difference. However, this 2dB puts the total above the defense response threshold. Throughput is suddenly decreased by 28dB, making the total reaching the inner ear 26dB lower than it was at 89dB external loudness.

A 26dB decrease should be much more noticeable than a 2dB increase, so our experience should be that things are suddenly quieter rather than louder. Also, some lower level components that were still easily enough heard should suddenly disappear from perception. I don't believe I've ever noticed such a thing or read of anyone describing such an experience. What am I missing?
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Reply #6
« on: September 26, 2007, 10:29:22 PM »
SteveG Offline
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So, it would seem then that the physical effects on the hearing mechanisms of this low level audio, whatever those effects may be, are possibly modified but little by environmental noise, as long as the total level reaching the eardrum does not exceed 90dB. At higher levels of environmental noise the signal will be attenuated by 28dB, so its efficacy almost certainly has to be greatly diminished. A reasonable summary?

No, not quite...

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I'm guessing the 0dB in this consideration is the threshold of hearing. Some particular amount of sound energy in the air equates to this 0dB, no? Is that only at a certain frequency, perhaps in that part of the audio spectrum where human hearing is most sensitive? Is it not the case that the sound pressure level must be higher to be heard at all in other parts of the audio spectrum?

It's the agreed sensitivity at the most sensitive frequency - around 2-3 kHz. And it represents a pressure of 2 x 10-5 Pascals. It's not really an energy measurement - that would be a measure of intensity - it's a measurement of pressure, although in any given direction, they are related. It gets a lot more complicated to explain this further, so I'm not going into any more detail here, because it's not particularly relevant to this.

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Is the 90dB increases that trips the defense mechanism at a particular frequency? Will a frequency restricted sound, such as a loud 18kHz tone, produce the same result?

Who said that anything 'trips' it as such? I said 'up to 28db' - it acts rather more like a compressor, not a limiter, and takes effect gradually. It's not particularly linear, though. And yes, loud enough 18k will excite the mechanism, certainly in young children - although it has to be pretty directional. And that sort of stuff is dangerous, because you can't easily detect it, but it can still damage you. But since the control mechanism is autonomously triggered by excess cochleal activity, it would appear, then if you have nerve damage this will adversely affect the mechanism anyway.

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Something seems wrong with the description of this mechanism. {etc} What am I missing?

I just told you... although there is in fact rather more to the basics of sound than I have described.
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Reply #7
« on: September 27, 2007, 08:47:57 AM »
AndyH Offline
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I pondered what happens at this 90dB point. Acting over a range seemed more reasonable than a sudden change in function, but you seemed to be suggesting that things were much different above 90dB. Up to 28dB could simply mean that the result isn't exactly the same for each person or isn't exactly the same for each stimulus.

Clearly I came to the wrong conclusion. Therefore at 91dB total input, the physical effects of the therapy music, whatever those may be, will be just somewhat reduced compared to when total input is 89dB, at 92dB they will be somewhat less than at 91dB, etc..

What is the range of action, 90dB to 96dB, 90dB to 110dB,  ... ? I suspect that before we get there we are in enough pain that we have no immediate concerns care about this therapy.

If the chart I just consulted is reasonably realistic, the in-automobile playing I was writing about isn't likely to involve this mechanism anyway. I don't have any way to make measurements, but the chart's example says 80dB is an office where typewriter (typewriter??) noise is high enough to require raising one's voice in order to be heard, and 90dB is the level of " Underground railway train passing." While both of those descriptions are open to interpretation, I don't believe their levels could be reasonably related to the circumstances of interest.

There exist sound level meters selling for under $50. Is it possible for such a devices to be accurate enough to determine reasonable figures for "in the car on the freeway" or "in the living room when the refrigerator is running" or "in the bedroom when the neighbor's dog is barking vs when the dog is not barking"?
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Reply #8
« on: September 27, 2007, 09:26:16 AM »
SteveG Offline
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What is the range of action, 90dB to 96dB, 90dB to 110dB,  ... ? I suspect that before we get there we are in enough pain that we have no immediate concerns care about this therapy.

It's not that loud - roughly the same as somebody shouting.

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If the chart I just consulted is reasonably realistic, the in-automobile playing I was writing about isn't likely to involve this mechanism anyway. I don't have any way to make measurements, but the chart's example says 80dB is an office where typewriter (typewriter??) noise is high enough to require raising one's voice in order to be heard, and 90dB is the level of " Underground railway train passing." While both of those descriptions are open to interpretation, I don't believe their levels could be reasonably related to the circumstances of interest.

The chart is about correct, by the sound of it (pun intended).

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There exist sound level meters selling for under $50. Is it possible for such a devices to be accurate enough to determine reasonable figures for "in the car on the freeway" or "in the living room when the refrigerator is running" or "in the bedroom when the neighbor's dog is barking vs when the dog is not barking"?

No sound level meter is any more accurate than the calibrator used to calibrate it, and since these cheap ones don't have one, and don't usually have ballistic responses that conform to the internationally agreed standards, they are pretty much useless for any meaningful measurements. The closest they get really is to give you an 'indication'... For all signifcant measurements, sound level meters are calibrated each time you use them. The calibrator on my system costs ten times what you are quoting for the meter, and the actual meter itself costs rather a lot more, as does the class 1 microphone you have to use with it. (Class 1 in this context is also a defined standard)
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