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Distortion Measurement with Soundcard and ARTA software
Distortion Measurement with Soundcard and ARTA software
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Old 11th September 2017, 09:24 PM   #1
djoffe is offline djoffe  United States
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Default Distortion Measurement with Soundcard and ARTA software

While I do have access to Audio Precision test equipment, many times it's much more convenient to do a sound-card based distortion measurement.

Here's a link to a youtube I made that shows an overview of how to do it, along with a schematic for a nice attenuator and limiter that you'll need to use on the input of the soundcard to make power amplifier measurements.

YouTube
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Old 13th September 2017, 01:50 PM   #2
mbrennwa is offline mbrennwa  Switzerland
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Distortion Measurement with Soundcard and ARTA software
Did you test the distortion of your external soundcard (Behringer UCA 202)? I am a bit puzzled of how you're getting such a clean signal from the UCA 202.
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Old 13th September 2017, 02:07 PM   #3
djoffe is offline djoffe  United States
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for the measurement shown, at 1 kHz, I used an oscillator of my own design that has about 2 PPM of distortion. It also has a 10K level control on the output, so there's not quantization noise issue.

As such, we're really only displaying the distortion of the A2D in the Behringer. so long as you don't overload it, its internal distortion is typically better than - 90 dB.
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Old 13th September 2017, 05:57 PM   #4
29285 is offline 29285  Europe
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Considering UCA 202 is a 16bit soundcard it is pretty good.
It is quite basic, all i/o is asymmetric. Looking for a replacement to measure bridged amp outputs I found the EMU-Tracker-Pre with symm inputs and 24bit resolution.
Dynamic range extends to about 110dB, loopback THD measurement at 1kHz drops to 0,0003% at medium levels.
It is my "poor man's AP"
The first plot shows EMU202, the second one the EMU Tracker Pre
Attached Images
File Type: png fft_uca202_loopback_minus_6dbfs_4000hz.png (23.5 KB, 1927 views)
File Type: png THD_5kHz_loopback_emu_tracker_symm_out_symm_in.png (33.1 KB, 1904 views)

Last edited by 29285; 13th September 2017 at 06:15 PM.
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Old 13th September 2017, 06:14 PM   #5
Joseph K is offline Joseph K  Hungary
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Nice video.
I use my EMU1616m a very similar way.
After the latest mods it measures like this below: (0.000072% at loopback, 1kHz -10db)
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File Type: jpg EMU_rightchan__1kHz_-10dbgen_48kHz.jpg (428.2 KB, 1891 views)
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Old 13th September 2017, 06:19 PM   #6
29285 is offline 29285  Europe
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That is excellent!
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Old 13th September 2017, 07:29 PM   #7
djoffe is offline djoffe  United States
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I also found this one...does anyone have experience with it?

ASUS Xonar U5 5.1-Channel USB Sound Card and Headphone XONAR U5

And...Joseph K...what mods did you make?...that one looks pretty darn good!
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Old 13th September 2017, 08:16 PM   #8
Joseph K is offline Joseph K  Hungary
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Dear Dan,

First of all, the EMU is using the AKM 5394A and is quite a good implementation by itself. The used njm2068D are very low noise, low distortion units. A bit slow, they are. So the opamp rolling to OPA1612-s did not bring much improvement in the basic frequency range but did bring down the distortion floor around 10kHz and above.

So the card started to become a 'tool', usable for testing the Myref composit amps.

Then the bypass capacitors around the ADC to organic polymers, more modern multilayer caps, removal of the output mute circuits in the dac - and lastly, what I could have known but tried only short ago: the AC coupling caps in the Dac output, usually bypassed by everyone, are essential for the Dac low distortion performance.. So the good old CS4398 is still capable of surprises.

The good thing is that this way the performance greatly stabilized through higher sample rates too; an optimal point is the 88khz sapling rate which is good enough for 20kHz distortion sweeps in STEPS and still gives a flat floor in the 0.00015% range.

The attach is done at 48kHz for bragging rights

Ps.: The card is multichannel, so there are three dac +three adc-s implemented. Two full channels can be freely used. They do perform slightly different. Choosing the best couple is another trick.

Ciao, George
Attached Images
File Type: jpg EMU_rightchan__steps_-10dbgen_48kHz.jpg (424.2 KB, 1856 views)

Last edited by Joseph K; 13th September 2017 at 08:20 PM.
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Old 13th September 2017, 11:56 PM   #9
29285 is offline 29285  Europe
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really impressive!
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Old 15th September 2017, 05:24 AM   #10
1audio is offline 1audio  United States
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Distortion Measurement with Soundcard and ARTA software
Thanks for your updates on the 1616M. The 1212M is very similar. Its possible to improve further if you have the complete circuit but its not published and the board is multilayer making that challenging. I have tried the LME49720's and they work but don't bring significant performance improvements. The cap upgrades may be more significant (not to mention replacing dead electrolytics, a common problem in the Emu stuff.)
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