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In Reply to: RE: Objective Measurement Results for Cables posted by Jon Risch on September 30, 2007 at 21:16:49
Looks interesting. Unfortunately without controlled listening tests it's impossible to know which of the effects they demonstrate are audible, or even which are the most important. What we really need is a series of listening tests that gradually vary one parameter of the cables at a time, thereby establishing audibility thresholds.
Edits: 10/01/07Follow Ups:
> What we really need is a series of listening tests that gradually vary one parameter of the cables at a time, thereby *establishing audibility thresholds*.>
Part of a test validation, perhaps.
You know, like in REAL science.
Do you know of any tests like this which have been done with other audio components?
Say, amplifiers?
I think it has been, at least partially - I know I've seen results for when THD in an amp becomes audible (several percent IIRC).
But I'm maybe missing the point of your post?
(nt)
> Unfortunately without controlled listening tests it's impossible to know
> which of the effects they demonstrate are audible, or even which are the
> most important.
Not at all if the measurements are sufficient. For example, if the authors labelled the y axis for the plots that curiously have the label "dB" but no numbers with, say, 1.0x10-6, 2.0x10-6,... would the effect of the different cables be above or below the threshold of audibility?
The point of science is to replace having to perform an experiment to find out something with scientific knowledge which can be used to predict the outcome of said experiment. Your statement implies this cannot be done for cables at audio frequencies and many people including myself would disagree for those cases where the size of the change is either well below or well above the expected threshold of audibility. When it is near the threshold then there may be a case for experimentation.
andy19191 wrote:
"Not at all if the measurements are sufficient. For example, if the authors labelled the y axis for the plots that curiously have the label "dB" but no numbers with, say, 1.0x10-6, 2.0x10-6,... "
As far as I can see, the graphs are labeled, with a visible range of 50 dB, and the level of the distortion products showing as high as "82 dB" or so.
After looking at the original AES article from CV engineers with the test signal modeled there, as well as actual measurements of some drivers in that same paper, the levels of the distortion products shown in the Newell and Howard paper implies a level that would have the primary tones at a level of 120-130 dB on that scale, meaning that the higher level distortion products are at -38 to -48 dB. My experience with reading and interpreting multitones, as well as the calculated modeling and actual measurements provided by the CV engineers provides a pretty solid base for this kind of assessment.
Note that many of these distortion products would be very aharmonic IM products, very plainly audible because they are not part of a harmonic series, but rather, at odd and unharmonicaly related frequencies. There are also more than just one of them, over a dozen clustered at levels within 10 dB of the highest ones. A veritable cacophony of odd ball distortion tones much harder to ignore than a simple 2nd or 3rd harmonic distortion product.
Jon Risch
> As far as I can see, the graphs are labeled, with a visible range of 50
> dB, and the level of the distortion products showing as high as "82 dB" or
> so.
I was referring to the later unlabelled graphs and in the context of my post the point was that measured minute differences are inaudible and the text was not overly reliable.
Concerning the figures you are referring to, I cannot offer anything without knowing what was measured, how and under what conditions. Without this one cannot work what is going on in terms of basic physics and hence determine if some magical property of cables has been discovered, a measurement misinterpretation/mistake revealed or whatever.
Anyway, if the CV engineers have provided a model for the effect then the physics is presumably understood. What is it?
...or is this an 'a priori' rejection?
andy19191 wrote:
"I was referring to the later unlabelled graphs and in the context of my post the point was that measured minute differences are inaudible and the text was not overly reliable."
Which unlabeled graphs?
Minute differences? I wouldn't think that distortion that is at -38 to -48 dB is 'minute', especially since there are more than one distortion product showing at or near those levels. If there were just 4 products at that level, then the total distortion would be in the range of approx. -32 to -42 dB, hardly something that one could call 'minute' or wish away as if it were insignificant.
And what in the world does "text not overly reliable" mean? Is this just another way of saying "I don't believe these people, and refuse to even entertain their data or arguments? How scientific is that?
andy19191 wrote:
"Anyway, if the CV engineers have provided a model for the effect then the physics is presumably understood. What is it?"
They modeled the amount of distortion that would occur with a particular multitone pattern due to the air and due to the horn placed on the driver (not including the driver's own distortions), and then compared that to an actual measurement of a typical driver, and an experimental one they were working on. Other work has modeled what the distortion pattern would look like with a certain (very low) amount of distortion, such as with a power amp. Finally, the measurements in the Newell and Howard paper show what the distortion levels are for a load resistor, and this provides a residual distortion level that is very similar to that of the previously modeled low amount of distortion.
No one has yet proposed a model for the distortion created by the amplifier/cable/loudspeaker combinations (that I am aware of). I would suspect that some one at CV or JBL might be working on it, and I have a few ideas myself, as well as having tried taking my own measurements of similar and related conditions, and seeing levels of distortion higher than load resistors and very short lengths of cable/wire.
Keep in mind that the length of the speaker cable under test in the Newell and Howard paper is 6M, or almost 20 feet.
Jon Risch
> Answer really wanted or is this an 'a priori' rejection?
I have an interest in how the performance of audiophile devices are presented. It is not a passionate one but it is real enough to read the odd paper when time permits.
> Which unlabeled graphs?
The unlabelled ones later in the article.
> And what in the world does "text not overly reliable" mean?
It means trying to make the data fit the belief rather than the other way round. Audiophiles performing experiments almost always do this and, so long as they honest, it usually does no harm in the scientific sense.
> They modeled the amount of distortion that would occur with a particular
> multitone pattern due to the air and due to the horn placed on the
> driver[...]
The modelling you describe does not include a model for the cable?
RBG with his imagined DBTs, you with your unlabelled graphs... you fellas are so creative!
.
No it doesn't - why would it imply that?
I think your point is simply that these thresholds have already been established, at least to a certain extent. I agree with that - but as you also pointed out the authors of those papers don't seem to have made much of an effort to match the measurements they made to any kind of audibility criteria, and that makes them not very useful.
Personally I doubt that these differences are audible except when the cables are either very long, very exotic (meaning high L, R, or C), or exposed to a high degree of RFI, but maybe there are exceptions.
> No it doesn't - why would it imply that?
Because you stated an experiment had to be performed to determine if the changes in cables was causing an audible change. I was trying to point out that a plot showing a variation of 0.000001 dB over the audible frequency range is sufficient to show an inaudible change in the signal.
> I agree with that - but as you also pointed out the authors of those
> papers don't seem to have made much of an effort to match the measurements
> they made to any kind of audibility criteria, and that makes them not very
> useful.
Yes but they are likely to be believers (I have not read the article yet) and this will be reflected in their words and how they go about things. So long as they provide honest data in a scientific manner this will not matter because they will be observing and reporting reality rather than just presenting their beliefs. Given their data one can compare it with standard audibility measurements from 50 years ago to see if it is well below, well above or somewhere near the threshold.
a
No. It would imply that normal designs under normal conditions are all the same in causing inaudible modifications to the signal (excluding the obvious).
If you were using the sound for purposes other than listening or the conditions were abnormal then there may be a case for considering the cable performance further. Or if you were developing marketing for the cable based on its actual performance but, then again, perhaps that would not be wise.
"If you were using the sound for purposes other than listening or the conditions were abnormal then there may be a case for considering the cable performance further"
And you base this conclusion on what?? Do you know the relevant thresholds for hearing these measureable differences??
a
If people are perceiving a difference due to what is going on between the ears rather than impinging on the ears then it would depend on what you are trying to achieve. Many people involved around here are trying to sell/believe in magic cables and so the answer is obviously yes. A few are only interested in getting cables good enough to avoid audibly distorting what is impinging on the ears and so if this is small enough then no.
I doubt seriously whether measurements cover all attributes of cables. If all the measurements cover are inaudible, I am certainly not convinced. I think science would advance more were studies to focus on finding the measurable characteristics of cables that most people prefer versus those they dislike.
> The key is "if people are imaging differences." What if they are not?
Who said they were imagining differences? Go look at the McGurk effect video. Is that your imagination or is that a real effect caused by your brain? Now map that onto the situation for cables.
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