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Old 14th September 2012, 10:56 AM   #7161
DF96 is offline DF96  England
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Quote:
Originally Posted by nigel pearson
is this paper saying anything ?
Fluids can be very non-linear, which can lead to chaotic behaviour. To get chaotic behaviour in an audio amp you either have to be smart or incompetent.
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Old 14th September 2012, 11:13 AM   #7162
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I did understand that . I just wondered could it be relevant ? As said I never found evidence .

My re-digitizing idea . I guess even vinyl could be used ? We can digitize the original and the output ?

Nordost gave a demonstration of this saying it would prove some debates could be answered . They seemed to think all errors showed up in the time domain rather than amplitude domain . I have heard nothing since so imagine they came unstuck ? The were using some RAF facilities which are used for aircraft analysis . They also had the ex RAF scientists to help .

http://www.nordost.com/default/downl...easurement.pdf
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Old 14th September 2012, 01:55 PM   #7163
DF96 is offline DF96  England
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As I understand the article, they took the analogue output from a CD player, converted it to (hopefully uncompressed) WAV format in a PC, then compared it with the original digital data. They believe this somehow measures the quality of CD playback. I hope I have misunderstood them, as all this does is measure the quality of the PC ADC.

The comparison achieves data alignment via some software they have written (for analysing sonar?).

They find that there are differences in the two data streams, especially when the slew rate is high. The difference can be up to 10% of data MSB, or a timing error of up to two samples. Adding 'magic' ingredients (e.g. fancy mains cables, equipment stands) seems to improve things, and correlates with audible perceptions. Have I got it right?

Assuming their write-up was not a total fabrication, or written by a marketeer, then two things are glaringly obvious:
1. As mentioned above, they are actually testing their ADC as much as anything else.
2. A 2 sample data error is simply not possible, unless one of the replay methods has a seriously wonky clock. I suspect that their time-alignment software was fiddling with the time delays as the test was running, and it gets confused by high slew rates in the data.

To do the test properly, you would need synchronised clocks (not mentioned) and an ADC which significantly betters (not mentioned) the CD standard (not to mention near perfect anti-aliasing filters). As usual, the MoD is lurking in the background. I hope not too much of my taxes have been paid to this outfit for their sonar work.

It is reassuring that the 'evidence' for magic potions continues to be so incompetent, as it helps confirm that the doubters like me are right.

PS Extra thought: some timing errors actually guaranteed unless clocks synchonised, so I think this confirms that their software would have to track the data dynamically (like a PLL) so almost certainly they are seeing software limitations.

Last edited by DF96; 14th September 2012 at 02:01 PM. Reason: add PS
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Old 14th September 2012, 02:19 PM   #7164
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This is why I thought a Vinyl source a better choice . It is a complex signal which could be digitized simultaneously by the same ADC ( in / out ) . It could be as many bits as one required . One might say an already digital signal might make life too simple ( pre-digested ) . Someone said it was the slight wrongness of a Garrard 401 which was great for testing digital recording devices . Mature Cheddar so to speak . Mild Cheddar should not result .

I suspect the Audio community will not join the bandwagon with this as it costs money and some will be a bit frightened . I talked to Richard Black and Tim de Paravacini with similar observations . The latter said approximately " tried it and it doesn't work " . The problem seems to be like null tests , is the null reliable . I suspect it doesn't require the last word in ADC ( 24 bit seems wise ) , just that it truly measures what is says it will and is repeatable . I would even include a heater in my test box as it would make one simple variant assured ( 45 C ) .

If we here could devise a simple test using cheap parts it would be great . It would be nice to find it did measure something we hadn't imagined possible . Perhaps the effect of vibration on DAC's or the like ( pulled from thin air as an example , Naim told me Philips have measured it when 16 bit DACs , Bleutak on top is all it requires ) . Nordost running the show is not my idea of objectivity .
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Old 14th September 2012, 02:44 PM   #7165
DF96 is offline DF96  England
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I have just noticed that the author of that piece is responsible for marketing at Nordost. Before that he was an audio journalist. Need I say more?
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Old 14th September 2012, 03:48 PM   #7166
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He was just the mouth of the company . Shame I never had the e-mail of the designer of the system . He seemed very aware of the questions we might ask .

I think if these ideas are reliable they will be seen and used . Noel Keywood is a journalist and is able to debate such things . Richard Black is no fool by a long way . Martin Collloms is sensible as is Barry Fox .
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Old 14th September 2012, 06:58 PM   #7167
DF96 is offline DF96  England
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It would be interesting to see a technical version of that article, so we can find out exactly what they did and what results they got. The marketing version doesn't even have legible numbers on the graph axes.
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Old 14th September 2012, 11:31 PM   #7168
tvrgeek is offline tvrgeek  United States
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Even I can see so many holes in that paper to dismiss it as Madison Ave. Engineering. They are comparing the outputs of two totally different DAC's. Nothing more than one cap could make the difference in the measurement, let alone the clocking of the "high quality sound card" 10 pages of BS. But then again, they are selling power cords.
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Old 15th September 2012, 09:44 AM   #7169
DF96 is offline DF96  England
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Yes, the more I think about that paper the more silly it seems. The main thing they will be seeing is phase shifts caused by the reconstruction filter in the CD player and anti-alias filter in the sound card, together with changes from asynchronous resampling. Then on top of that they either see some crystal clock wandering (probably inaudible anyway) or their software trying to compensate for this. If there is any tiny bit of real problem in there it can be solved by using better clocks: better crystals, better PSUs, not magic cables.

The brains behind this work might be brilliant on sonar, but perhaps not quite up to speed on digital audio?
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Old 15th September 2012, 10:40 AM   #7170
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I would ask him to join us . I may have cooked my goose by criticizing his journalist ( Nordost paper ) ?

The test has to stand examination if it is to succeed .
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