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Old 3rd March 2010, 02:59 AM   #951
PB2 is offline PB2  United States
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Quote:
Originally Posted by Joachim Gerhard View Post
Talk abour spiders. They are the biggest source of distortion in a speakers and Prof.Dr.Klippel has devoted the best part of his life to research that phenomenon.
Talking about distortion in tube amps my friends at Test Factory, an independent institute in Germany that also works for Audio and Streoplay magazine found a distortion mechanism in poweramps that happens in the first 100msec after an impulse. Most tube ams and amps with low or no overal feedback did much better on this test then amps with high lokal feedback. Ironically Prof.Dr.Hawsford found similar (but not same) resolution problems with high feedback circuits in very low level stages. For me the doors are still open. We do not understand everything hopefully or i whould quit my job. When a 100,-€ Blue Ray player is perfect i see no reason to work in this bussiness.
The hardcore scientist whoud of cause argue that this subjective debate has already setled in the 60th so the only raison déntre is to make things cheaper and smaller.
Brave new world.
Any unusual distortion mechanism would show up in a null test. Null testing has been used for many years as I'm sure you know. Don't care for his SIM name but the Baxandall configuration is also shown here: "Sound Impairment Monitor (SIM) - Is This The Answer?"

There is also the Hafler configuration for power amp testing.
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Old 3rd March 2010, 04:18 AM   #952
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I used both, the Baxandall and the Hafter test. You can do that digitally now. You can download the "Diff Maker" from Liberty Instruments for free.
Liberty Instruments, Inc. Home Page
Two amps i tested with the diff maker made a fantastic null but when i put them in my system they left a lot to be desired.
I can not explain at the moment why that is so.
When i whould try an explanation a lot of people whould think i am a subjectvist, and reading my theatrice is a waste of time. I did that mistake some years ago when i published my work about cables on the net. I was really surprised how seriously offended some people reacted only because i said that my measurements could explain SOME audible differences.
Still i allow my privat experience to shine through here sometimes.
This is the reason i called this thread MPP ( My Privat Phonosatge).
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Old 3rd March 2010, 11:57 AM   #953
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Dear Joachim,

I can confirm your experience about the Diff-Maker test. I had it as a prototype version in my own software and found out that it was not corresponding to the results of a listening test. Good measurents did not necessarily mean good sound. But I'm used to this effect ;-) Anyway, it was very interesting and funny to play around with it. So I keep going for the built-in Belcher test and it's successor noise-distortion test in my analyzer that gives me more informations in relation to listening results. Of course it is necessary to understand the graphs, but that is more a thing of practice and experience. Have fun!
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Old 3rd March 2010, 05:06 PM   #954
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JurgenU, you are right. We have done the same thing, and found it wanting. We hear differences, yet a fairly straight forward differential test may show little or nothing.
I remember back in 1974 when we had our first FFT differential test (10bits) and we tried to do it with IC's vs discrete op amp designs. The differences were lost in the noise. It really impressed my associate, John Meyer, and he virtually became contemptuous of me, because his SPEAKERS showed BIG differences, and my IC's showed small, if even measurable differences. Years later, he went to use IC's almost completely, thinking that they were not audible, as they were not easily measurable. A big mistake, in my opinion.
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Old 3rd March 2010, 05:07 PM   #955
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Is the Belcher test, the noise loading test? (BBC, I think?)
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Old 3rd March 2010, 07:03 PM   #956
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Dear John,

Belcher test is the one suggested by R.A. Belcher. Here is a rough explanation (Belcher.pdf)

Measurement is shown in the pictures Belcher2.gif (with stimuli shown)
and Belcher2.gif (stimuli removed)


One of my favorites is the noise distortion measurement ( it is even more sensitive to distortions )
It is a kind of THD measurement using a band limited noise carrier as test signal. The level outside the noise carrier band is measured and related to the total level. Stimulus and analysis range are separated by a kind of brick wall filter with Kaiser window (highest side lobe damping).
The picture noisedistortion.gif shows the measurement.

I hope all data are legible, this board is a bit tricky, not sure if it works.
Attached Images
File Type: gif Belcher2.GIF (45.2 KB, 267 views)
File Type: gif Belcher1.GIF (28.8 KB, 265 views)
File Type: gif noisedistortion.GIF (34.7 KB, 265 views)
Attached Files
File Type: pdf belcher.pdf (66.9 KB, 28 views)
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Old 3rd March 2010, 09:49 PM   #957
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I use this test all the time and when you go back in this thread you will see that i posted some measurement. I think in the US it is known as spectral contamination.
Deane Jensen did a paper about that and there is some work from Rich about the optimum patter. Prof. Dr. Klippel uses something simimiliar that he calls "Sparse Spectrum".
I have a highly modified DAAS, a Klippel Distortion Analyser and i am the German importer of Praxis so i have a lot of experience with this test. It is also very telling in loudspeakers. I recently developped a new dome tweeter with SEAS. On the outside it looks very unspectacular and it is not even very expensive, but we where able to reduce spectral contamination by 6dB.
The sound got much better too. The resolution is now nearly as good as with a ribbon.
My reference is the big RAAL with amorfous core.
I whould really like to publish more measurement but my lab gets totaly new build and i will not be able to use it until mid april.
I also was helpfull to develop the distortion isolation Script in Praxis and that could be the solution for our quest. I just whould like to implement it in 24bit.
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Old 3rd March 2010, 11:34 PM   #958
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Quote:
Originally Posted by Joachim Gerhard View Post
I use this test all the time and when you go back in this thread you will see that i posted some measurement.
Of course I know this, Joachim.
Explanation of the measurement was mainly for John, because he asked for it and I suppose he does not know this analyzer because it is nearly unknown in the U.S.
;-)
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Old 4th March 2010, 12:43 AM   #959
PB2 is offline PB2  United States
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Quote:
Originally Posted by Joachim Gerhard View Post
I used both, the Baxandall and the Hafter test. You can do that digitally now. You can download the "Diff Maker" from Liberty Instruments for free.
Liberty Instruments, Inc. Home Page
Two amps i tested with the diff maker made a fantastic null but when i put them in my system they left a lot to be desired.
I can not explain at the moment why that is so.
When i whould try an explanation a lot of people whould think i am a subjectvist, and reading my theatrice is a waste of time. I did that mistake some years ago when i published my work about cables on the net. I was really surprised how seriously offended some people reacted only because i said that my measurements could explain SOME audible differences.
Still i allow my privat experience to shine through here sometimes.
This is the reason i called this thread MPP ( My Privat Phonosatge).
Yes, I'm aware of Diff Maker and I've used Bill Waslo's LAUD from Liberty Instruments for more than 10 years.

My point is that if anyone speculates on some sort of yet undefined form of distortion it will show up in a null test.

You mentioned something happening in the first 100 mS of a transient - 100 mS is a long time and it would surely show up in a null test. Did you mean uS ?
Mpp

I'm not saying that I agree that this is a problem in any good amplifier.
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Last edited by PB2; 4th March 2010 at 12:46 AM.
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Old 4th March 2010, 12:50 AM   #960
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Quote:
Originally Posted by john curl View Post
Dynamic headroom is really based on the amount of high frequency, well above 20KHz that effects phono cartridges most. This can extend to above 200KHz on a regular basis.
I'd call this high frequency headroom to indicate that the emphasis is on HF, but as I see it there is nothing dynamic about it. It does not change with level or time. OK, perhaps it is nit picking ....
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