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Old 26th September 2007, 07:39 PM   #7711
6h5c is offline 6h5c  Netherlands
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Quote:
Originally posted by SimontY
Ray, the starter of this fine thread, is hoping to measure jitter soon.

Simon
Quote:
Originally posted by ezkcdude
Ray might have some opinions on measuring, since he's been doing quite a bit lately (from what I hear).
And fine it is indeed!
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Here's a screenshot of one of the first jitter measurements I did last week. I'm still busy interpreting the results...anyone?

Ray
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Old 26th September 2007, 07:45 PM   #7712
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I must have gone blind!
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Old 26th September 2007, 07:47 PM   #7713
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Blink again... there's it is
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Old 26th September 2007, 07:51 PM   #7714
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I have so many questions. 1) What type of test is this? 2) What is the DUT (device under test)? and 3) Is the number we should be looking at the mean (43 ps)?
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Old 26th September 2007, 08:08 PM   #7715
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Default Jitter measurements

I can answer the first two . The wave on the screen is the slope of the stretched clock signal of a Flea with Tentlabs XO. The measurement is RMS Jitter which requires the color-grade view switched on. Every color stands for a certain range of values, and the scope uses this to gather statistics.

Here's another nice one, this one uses a histogram to display the jitter distribution.
If i'm correct, jitter is the deviation in time from the actual correct slope, which would theoretically be rock solid in the center of the color trace. So the peak-to peak deviation is 163ps, and actual peak-peak jitter would be about half that value (if i'm right?), because the deviation can be positive as well as negative. How this converts to RMS jitter I don't know (yet). The standard deviation 'std dev' or also called sigma, is a statistical value and it describes the spread of the values around the mean value.

I don't exactly know (yet) how to interpret this data, still working on that. Maybe Guido can help us out?

Regards,

Ray
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Old 26th September 2007, 08:52 PM   #7716
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I think the important number here may be sigma (std dev). Here's a figure I found:

Click the image to open in full size.

If this is true, 19 ps seems like a pretty good number, right?
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Old 26th September 2007, 10:21 PM   #7717
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Yes, 19ps would be good, but of more interest would be the jitter right at the DAC pin, as this is where it makes a difference I would think.
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Old 26th September 2007, 11:01 PM   #7718
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Quote:
Originally posted by Pars

Interesting. I too use RMAA with an M-Audio Firewire Audiophile external box. I haven't ever used it on a CD player and was wondering how you were doing this, given that a CD player doesn't have analog inputs? Are you recording a test CD using RMAA and measuring the playback of it?

I am currently doing a couple of discrete I/V stages for my Rotel 855 and was using RMAA on these... mainly because I could . I had started to think about being able to measure the entire CD player once I installed these, and to see what differences between the discrete vs. opamps stages, etc. I could see.

This is a most interesting thread, although I have to confess I haven't read ALL of it.

I have recorded a test CD. It's very easy:
1) record CD with two tracks generated by RMAA
2) play first track on repeat to adjust recording level
3) start test by recording the second track

I find it very, very interesting to see what comes out. In this way you can test the effect of all changes you make. Even if the absolute measured levels are not quite correct, you still get some trends.
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Old 26th September 2007, 11:13 PM   #7719
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Quote:
Originally posted by ezkcdude
I question the measurements above, because the sound card is not a good one. The DNR for a good soundcard (like my E-MU 1212) is around 117 dB. This USB card is only 1-2 dB above what the CD player is measuring. Please note I am not questioning your mod or the listening results, just the measurement test.

Just to back up my point a little, someone did measurements on my ezDAC a while back with an E-MU 0404 USB, and you can clearly see the difference between the 16-bit and 24-bit tests (with the 24-bit tests 12 dB higher).

http://haowulin.googlepages.com/Comparison.htm

Ray might have some opinions on measuring, since he's been doing quite a bit lately (from what I hear).

Well, this is a much better sound card than my previous Creative Audigy 2 NX USB. I can also confirm that there are some differences when recording at differenet sample rates and resolutions. But this is still suitable for comparision and trend measurement. For instance, I was able to clearly see the dynamic range of my old PHILIPS CD 723 changing form 94 dB to 89 dB when adjusting the volume via the digital volume control from 100 % to 50 %. Another good idea is to repeat the tests in order to see if there are some stochastic influences. Before posting those results, I repeated all tests 2-3 times.
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Old 27th September 2007, 12:00 AM   #7720
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Default Photos of the installed Tentlab XO

Here are some pictures of the newly installed clock.

http://www.sinigersky.com/images/Mar...67-Clock-1.jpg

http://www.sinigersky.com/images/Mar...67-Clock-2.jpg

I have treated the clock as a high frequency device (16.9344 MHz is in the short wave range!) so I use a screen and a coaxial cable.
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