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Old 18th November 2011, 07:23 PM   #18071
jcx is offline jcx  United States
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that's a lame example - instrumentation designers have known of DA error relative magnitude between dielectrics for a long human lifetime

BSTJ has "3-D" plots of polyester dielectric cap errors with frequency, temperature from characterizing them for telephone filters/eq

"real", "conventional" engineers do appreciate device differences exist, are quantifiable, give measureably different circuit results

in fact these parts selection hints are one of the reasons I follow the thread at all

but I certainly don't believe the "explainations" often offered when they are easily shown to be of absurd low magnitudes releative the the other audio reproduction errors
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Old 18th November 2011, 07:31 PM   #18072
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but I certainly don't believe the "explainations" often offered when they are easily shown to be of absurd low magnitudes releative the the other audio reproduction errors
Log scale, examination of macro rather than low level signals, overlooking of details.
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Old 18th November 2011, 07:31 PM   #18073
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Of course, PMA, it is OBVIOUS in hindsight. '-) I had a brief fantasy of being a consultant for a firm with the same problem, and how 'obvious' it would have been to check for DA effects in any caps. Like you, I sometimes do this sort of thing as part of making a living. It is interesting that you call a 'tail' was described to me as 'echo' once in WW or HFN and I never heard the end of it, but it was obvious in the test that Walt Jung and Scott Wurcer developed to test DA in caps, and I used for Walt's and my paper on the subject.
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Old 18th November 2011, 07:49 PM   #18074
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Today I had an interesting feedback from my customer. Not audio, but measuring systems. The issue was input voltage divider (R//C) of the data acquisition system - transient recorder with fiber optic signal transmission. The problem was that step response has had unexpectedly wide settling error band. Not a typical overshoot, but rather long tail settling. We have been trying to find the real reason for years. Today he called me he has finally solved the problem. He has exchanged the polyester capacitor in the input compensated divider for the polypropylene cap - and the long tail settling disappeared. The issues are same as in audio ...
I guess he never read Bob Pease's article, very old news.

EDIT - Does we include you, you certainly know this?
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Last edited by scott wurcer; 18th November 2011 at 07:57 PM.
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Old 18th November 2011, 08:19 PM   #18075
SY is offline SY  United States
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Either I am 'crazy' or the ABX test makes different things sound virtually the same, during the test, and yet different in open listening, or even A-B comparisons. It is for you to chose.
Many other possibilities. And there's nothing magic about ABX, there are a lot of good ways of doing "ears only" tests. But we've been through that over and over. Some of us trust our ears, others rely on eyes and preconception.

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Old 19th November 2011, 04:01 AM   #18076
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Don't worry PMA, Scott doesn't believe that it is important for 'audio' in any case. I beg to differ, as does Walt Jung. In fact, Walt sent Lipshitz et al the very WORST tantalums that he had determined by listening, and they could not sort them in an ABX test. What then, is the point? If anyone does not believe me, ask Walt Jung, yourself.
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Old 19th November 2011, 04:07 AM   #18077
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Yes, as SY implies, I am paid for finding 'differences' rather than maintaining that audio is virtually perfect, and a cheaper solution is just as good as an exotic one. Therefore, I am tainted and you should not listen to my input. You have been warned!
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Old 19th November 2011, 04:24 AM   #18078
SY is offline SY  United States
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Yes, as SY implies, I am paid for finding 'differences' rather than maintaining that audio is virtually perfect...
Of course no-one maintains that "audio" is perfect, but hey, if that's what you need for an argument, go for it.

I assume that Walt Jung didn't sort those caps by ear alone either.

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What then, is the point?
The point is that there are many things which cause audible differences. There are many things that don't. The way to tell one from the other is by ear, not by eye.
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Old 19th November 2011, 04:27 AM   #18079
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Ask him.
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Old 19th November 2011, 06:11 AM   #18080
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PMA do you have Bob Pease's article on dielectric 'soakage'? It is good to have for 'completeness'. Walt and I referenced it in our article on DA in TAA and HFN back in the 1980's.

Last edited by john curl; 19th November 2011 at 06:41 AM.
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