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Old 17th April 2013, 11:49 AM   #1101
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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, 11:53 AM   #1102
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Exactly! The trick is how to get the difference down to -160dB.
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Old 17th April 2013, 01:30 PM   #1103
Waly is offline Waly  United Kingdom
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Quote:
Originally Posted by Edmond Stuart View Post
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 01:36 PM.
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Old 17th April 2013, 03:07 PM   #1104
BV is offline BV  Slovakia
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Quote:
And BTW, balanced inputs do look nice for advertising purposes, for measuring single ended power amps they are pretty much useless.
It is very simple to convert balanced input to differential input for measuring single ended amps, with all benefits for differential input.
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Old 17th April 2013, 03:17 PM   #1105
Waly is offline Waly  United Kingdom
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Quote:
Originally Posted by BV View Post
It is very simple to convert balanced input to differential input for measuring single ended amps, with all benefits for differential input.
No, not at -160dB.
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Old 17th April 2013, 03:52 PM   #1106
BV is offline BV  Slovakia
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You stated
Quote:
for measuring single ended power amps they(balanced inputs) are pretty much useless.
This is simply not true, they can very well supress ground currents influence at measuring (mains and harmonics) . No one talks that it can help to reach -160dB noise background..
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Old 17th April 2013, 04:26 PM   #1107
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Quote:
Originally Posted by BV View Post
You stated
This is simply not true, they can very well supress ground currents influence at measuring (mains and harmonics) . No one talks that it can help to reach -160dB noise background..
Balancing is not necessary about "ground currents influence", but about common mode noise/artifacts.

If you can't reach better than -160dB floor in unbalanced configurations, then what's the point of specifying -160dB measurements.

Not sure what's the floor in Edmond's result, -210dB is suggested. That would be around 32 picovolts. Synchronous averaging (for 8 hours?) lowers the floor, but not the correlated common mode noise/artifacts.

My suggestion was to integrate and test the software with current (and much cheaper) sound card models. Expecting the diy potential customers to buy a L22 for the luxury of measuring ppb distortions (who cares about, anyway?) it's in my opinion not realistic.
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Old 18th April 2013, 09:42 AM   #1108
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Hey BV,

The THD figures you showed on post 1102 are exceptional low: 0.2ppm respectively 0.4ppm. Please tell me which sound card (brand & model) performs so extremely well?

Cheers,
E.
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Old 18th April 2013, 10:34 AM   #1109
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It is "snobbish" Lynx L22. But it is mandatory to keep input/outputs levels near 1V RMS (0 dBFS is about 7V RMS, balanced), where distortion are lowest .
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Old 18th April 2013, 11:35 AM   #1110
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Default L22

Hi BV,

Under the same conditions I got a slightly higher THD (-122 to -126dB), depending on which channel and which L22. Yes, I have two them, bought on ebay at roughly the same price as a new ASUS blah blah blah XTe thingy. Really 'snobbish', isn't it.
So you also noticed that near FS (in the yellow zone) distortion rises significantly. Any idea which IC in particular is responsible for it?
I think it's the INA137 or the MC33078 in the first place.

Cheers,
E.

BTW, what's your real name?
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