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Old 11th August 2012, 09:53 AM   #26011
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These two waveforms have SAME amplitude spectra, they only differ in a phase (-180) of one of the spectral components:
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File Type: png fourier2.PNG (37.3 KB, 165 views)
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Old 11th August 2012, 12:29 PM   #26012
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Quote:
Originally Posted by janneman View Post
Ian Hegglun has an interesting article in Linear Audio Vol 4 about weighing regular THD measurements giving results that appear to correlate quite well with listening tests.
For instance, it has always been difficult to express the measurend xover distortion in numbers correlating with listening tests because their effect depends so much on dynamic issues, signal levels etc.
With Ian's weighing principle the correlations seems much better.

jan
Something that Ben Duncan was suggesting in HiFi News, oohh, at a quick guess, in the region of over 20 years ago ...

Frank
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Old 11th August 2012, 12:42 PM   #26013
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Gordon Holt, long before that.
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Old 11th August 2012, 01:13 PM   #26014
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Default power cords

http://www.russandrews.com/images/ar...ion16Feb09.pdf

http://www.russandrews.com/images/ar...rGraphsDoc.pdf

http://www.russandrews.com/downloads/SKtest.pdf

http://www.russandrews.com/downloads...estPremRes.pdf

Last edited by dimitri; 11th August 2012 at 01:24 PM.
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Old 11th August 2012, 01:16 PM   #26015
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The ransom note typography is particularly delicious.
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Old 11th August 2012, 02:00 PM   #26016
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Quote:
Originally Posted by RNMarsh View Post
Thank you for putting it here at this time. It certainly needs to be done asap. Its been way, way too long in coming. The data on many FFT can be found in a list of the actual measured values that are plotted. If this data was in a spread sheet, it would be just as easy to add the weighting and replot the data. Then we will have something better to correlate and make refinements to it and we are on our way to more meaningful tests/measurements.

Any takers to work on this project?? maybe Audio Precision? -RNM

Mr. Geddes has been disappointed on the "no response" from the part of the audio professional sector.
I can’t say what their explanations are.

From my amateurish part, I would really like to be able to test his metric.
Alas, I don’t know how to handle the formula for Gm in practice.

This formula calls for the analytical form of the DUT’s transfer characteristic. This is not good news for me, or at least I can not see how to handle it.

I can vary the signal level and have the DUT output/input recorded through a soundcard. Then transform these two signals into data pairs and have them imported on a spreadsheet. Then what?

I can also have the output & input of the DUT entered into a spreadsheet, the FFT of which (the amplitude and phase of the harmonics) are calculated and displayed and where manipulation (weighting) can be applied onto them. Then what?


George
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Last edited by gpapag; 11th August 2012 at 02:06 PM.
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Old 11th August 2012, 02:05 PM   #26017
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Well at least they are honest about it.

"Similarly, the graphs do not prove that the rejection
measured in the lab has a perceptible (ie audible) effect
when the cables are used in a Hi-Fi or Home Cinema System."

And to their credit they did good testing. But if you need power cords with RF rejection, wouldn't simple shielded mains cable be easier?
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Old 11th August 2012, 02:17 PM   #26018
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Quote:
Originally Posted by gpapag View Post
I would like to ask if there is a way to derive the Gedlee Metric of the DUT from the FFT (amplitude and phase of the harmonics) of the output (OK at some different signal levels too)?

http://www.gedlee.com/downloads/THD_.pdf

George
George, I have asked several times without answer, "Does the metric hold when all distortions are -100dB or so?" Earl has implied several times that it is relatively easy these days to find electronics that are "transparent", and my impression is he does not believe in most (any?) of the extreme beliefs.
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Old 11th August 2012, 02:18 PM   #26019
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George, remember that the metric is useful for loudspeakers- nearly any competent amp will score exceptionally well, which is why Earl uses a cheap Japanese amp and worries about more important things.

edit: xpost with Scott
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Old 11th August 2012, 02:34 PM   #26020
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Quote:
Originally Posted by jcx View Post
I once tried a direct encode/decode experiment which showed single sine had ~ -80d spurs&distortion Schematics needed for 3V 1KHz Sine wave generator

I did a different experiment, encode a 1 min. 60Hz sine wave and then add one cycle over the whole minute. The output was perfect even at 128k encoding.
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