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Old 29th March 2013, 04:56 AM   #1101
jcx is offline jcx  United States
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The problem with ALL these damn sound cards, is the only decent ones are the ones that slot into a motherboard. I want this performance on a USB line input level unit. I tried a few(EMU, etc). All crap. But, just for doing comparative measurements, I suppose they will do. Maybe we could stop throwing eggs at each other and design a really good stand lone card.
I think Twisted Pear are working on ESS ADC too

but maybe non ESS parts would be preferable for a "open" design
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Old 29th March 2013, 10:18 AM   #1102
BV is offline BV  Slovakia
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you have to be either a snob, or equally rich and stupid.
Try something like this (analogue loopback, BW10kHz) with your card..And more than ten years ago.
"We are not so rich to buy cheap things.."
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Old 17th April 2013, 08:25 AM   #1103
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And this is what can be achieved with my distortion analyzer and 10 years old sound card:
Test signal: 19201Hz, BW: 250kHz, measurement floor < -160dB. Harmonics are around 2ppb. I wonder if this is possible with a Xonar Essence, despite its gold plated bracket.
(NB: All done in software; no analog distortion magnifier or notch filter has been used.)
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Old 17th April 2013, 09:07 AM   #1104
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Edmond, I know I asked before but I still don't get how you are able to generate a 19 kHz test tone with -160 dB harmonics in a 250 kHz bandwidth. With the sound card? How????
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Old 17th April 2013, 09:54 AM   #1105
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Hi Harry,

I don't generate a 19 kHz test tone with -160 dB harmonics, instead, the measurement floor of the whole setup is 160dB down. How? Sorry, I can't tell because of commercial interest. The same applies to that 250kHz bandwidth, which, btw, is not the BW of the sound card (normally Fs/2), rather a constraint imposed by the software.
(The 'software' BW is much higher than Fs/2. Hint: think of undersampling).

Cheers,
E.
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Old 17th April 2013, 10:21 AM   #1106
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Originally Posted by Edmond Stuart View Post
Hi Harry,

I don't generate a 19 kHz test tone with -160 dB harmonics
Then I obviously don't understand what you mean by:

Quote:
Originally Posted by Edmond Stuart View Post
Test signal: 19201Hz, BW: 250kHz … Harmonics are around 2ppb
Or your screenshot showing a sinewave and a measurement reading that states "THD = -168.2 dB"

Where is that sinewave coming from?
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Old 17th April 2013, 10:30 AM   #1107
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Hi Harry,

The screenshot shows what you get if the DUT produces zero distortion.

Cheers,
E.
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Old 17th April 2013, 10:49 AM   #1108
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OK, so your input signal to the DUT actually has much higher than -160 dB distortion? Then you're doing some kind of difference function between input and output of the DUT to remove the harmonics present in the test signal?
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Old 17th April 2013, 10:53 AM   #1109
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Exactly! The trick is how to get the difference down to -160dB.
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Old 17th April 2013, 12:30 PM   #1110
Waly is offline Waly  United Kingdom
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How? Sorry, I can't tell because of commercial interest.
Now I understand - you are looking for funding for your next amp construction. You are going to be a very rich man in the audio business! What about moving this to the Commercial Sector on this forum?

I have no idea how you implemented this in software, but spectra substraction is available in almost every DSP software package that I know, all free of charge. It's not rocket science, spectral components have to be substracted as vectors, so with both magnitude and phase.

Try the M-Audio 192 or the Xonar before you speak (not that I would expect from you a shadow of objectivity). And BTW, balanced inputs do look nice for advertising purposes, for measuring single ended power amps they are pretty much useless.

P.S. Averaging for 8 hours?

Last edited by Waly; 17th April 2013 at 12:36 PM.
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