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Author Topic: Yggdrasil Measurements  (Read 8533 times)

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atomicbob

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Re: Yggdrasil Measurements
« Reply #40 on: May 16, 2015, 05:47:04 PM »

I've done some more reading to try and understand all this. The PCM1704 chips implement signed magnitude so I wouldn't expect to see any cross over distortion. But my waveform SSs also aren't zoomed in to the scale you mentioned so it may not be evident (if it exists). One thing I still don't understand is reconciliation of the rated distortion figures of the AD chips vs the distortion measurements - is what you've measured within spec of +/- 1 LSB? (Probably because I don't understand the DBFS scale lol.... Next thing to read up on).

I'm not sure how Schiit have implemented the chips per channel but I don't think it signed magnitude - prolly one chip per balanced hot signal.

My DSO is a Rigol DS1054Z (software upgraded).
Very good, thank-you. The DS1054Z has an 8 bit ADC for input with an ability to SW oversample to an equivalent of approx 12 bits. Maximum sensitivity is 1mV/div so it will be very hard to observe phenomena below 100uV. I have a picoscope 5243B which has a 16 bit ADC and same SW oversample feature to 20 bits, yet only has 2mV/div resolution. We both need a 20dB low noise probe amplifier to see this type of zero crossing distortion on our oscilloscopes. One of the reasons the dScope is sooo expensive. The front end resolution it can attain.
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ultrabike

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Re: Yggdrasil Measurements
« Reply #41 on: May 16, 2015, 06:33:38 PM »

I think scopes in general can do much higher sampling rates. Audio Analyzers don't go that high in sampling rate. Proly different ADCs.
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atomicbob

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Re: Yggdrasil Measurements
« Reply #42 on: May 16, 2015, 07:31:35 PM »

Here is a link to an ECN article which discusses the oversampling feature in an oscilloscope:

http://www.ecnmag.com/articles/2013/01/how-get-more-8-bits-your-8-bit-scope

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ultrabike

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Re: Yggdrasil Measurements
« Reply #43 on: May 16, 2015, 08:03:05 PM »

Yes. I can see that working out. May also depend on SNR.
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aive

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Re: Yggdrasil Measurements
« Reply #44 on: May 16, 2015, 10:40:02 PM »

Wowzors, -90 DBFS is a seriously tiny signal (0.00003162 of full scale voltage). Puts the mid-scale/zero crossing glitch amplitude in perspective...

Just out of curiosity, how does the time-domain vertical scale work in your graph? It's not consistent increments in DBFS between tick-marks? Not familiar with the Dscope meter.

And following what Solderdude said earlier, I'd expect these glitches to appear as second-harmonics (2 x Fo)? Which in this case is 2 kHz not at 17 kHz? I had this confirmed in a paper I read here - Page 5 of http://www.analog.com/media/en/training-seminars/tutorials/MT-013.pdf

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atomicbob

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Re: Yggdrasil Measurements
« Reply #45 on: May 16, 2015, 10:50:43 PM »

Indeed! Why neither Solderdude nor I am concerned about the zero crossing distortion. My graph is extremely magnified in the Y axis to see it. dScope information can be found here:
http://www.prismsound.com/test_measure/products_subs/dscope/dscope_home.php

The frequency is being estimated by looking at the x-axis glitch period and inverting.

May 17 my yggdrasil will hit 400 hrs. I hope to have some time free to repeat the measurements at the beginning of this thread and fill in those reserved posts.
« Last Edit: May 16, 2015, 11:35:35 PM by atomicbob »
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Solderdude

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Re: Yggdrasil Measurements
« Reply #46 on: May 17, 2015, 06:49:32 AM »

I should clarify that the artfifact shown (the crossover blib) is not a glitch as described in the linked article.
The glitches (which the used DAC chip indeed has) have already been removed.

The 0 crossing thing you see is (most likely) caused by DAC chip '1' taking over the positive half of the sign wave to the negative half of DAC chip '2'.
I suspect (no evidence here, just a hunch, I guess mr. Moffat or Jason can correct me) that the chips are in signed magnitude config (hence the 21 bit resolution with 2x 20 bit chips) and perhaps the 'blib' is caused by an extremely small DC offset between the '0Voutputs' of both signal halves where they are 'combined' to create the complete signal.
The 'size' of the blib may actually differ per Iggy as well.

In all cases ... the blib may be quite measurable, because the noise floor of the electronic itself is very low, but is so low in amplitude it will be inaudible.
The practical noise floor, with an actual audio signal on it, will be higher than better measuring/performing DAC's for sure but as mentioned before will still be much lower than any real world recording out there so will be 'masked'.

Indeed as atomicbob already answerred the 'fundamental frequency' of the blib is estimated by looking at the length of a known period (the actual sinewave of 1kHz) in millimeters on the screen and the periodlength of blib and simply dividing those numbers and multiply that result x 1kHz (the used sinewave).

As that 'blib' has 'sharp edges' it will also have harmonics but those are far above the audible range.

The amplitude of the blib is estimated in the same way by measuring (in peak mm's on the screen) a known amplitude (-90dB) and the amplitude of the blib and crunching some numbers.
There is no higher math, assumptions, or theories involved other than quite basic stuff.
« Last Edit: May 17, 2015, 07:13:22 AM by Solderdude »
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atomicbob

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Re: Yggdrasil Measurements
« Reply #47 on: May 17, 2015, 11:23:02 PM »

408 hour on time measurements now added. Now I'm going to listen to my damn schiit. If I don't come up for air, it is because I have lost track of time again. This DAC is truly that good!

Maybe next weekend I will get to the AES and s/pdif input measurements. I'm out of energy for today.
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Solderdude

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Re: Yggdrasil Measurements
« Reply #48 on: May 18, 2015, 04:41:22 AM »

No changes in measurements after that many hours ?
Jitter still the same ?
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atomicbob

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Re: Yggdrasil Measurements
« Reply #49 on: May 18, 2015, 04:58:21 AM »

The jitter spectrum improved significantly. Have a look at the graphs. They are now in the posts previously reserved on the first page of this thread.
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