I've put off doing measurements myself on the stuff I mod for a long time. It sounds like there are more affordable ways of measuring THD, etc. these days like sound cards and Analog Discovery (?), but posts don't really go into much detail and many of them are from years ago.
So, are sound cards usable for doing distortion measurements for DACs? If so, what are the steps?
So, are sound cards usable for doing distortion measurements for DACs? If so, what are the steps?
The problem these days is that DAC have gotten pretty good. If you want meaningful results, you'll need a good soundcard, especially ADC wise.
The first step would be to chose a soundcard fitting your budget and available interface (usb, pci, pcie, etc). If you want to test DACs with balanced outputs and fairly high output levels, you'll probably want at least something like the focusrite 2i2.
Then you have to check that the DAC isn't a danger to the soundcard. Does it have offset ? What is its maximum output level ?
Then you have to pick a software to record and analyze what's going on. Among others, there are ARTA, RMAA, audiotester. Once your choice is made, you have to properly configure it. That's very software dependent so it's hard to be too detailed right now.
Then you simply connect your DAC to your recording soundcard input and let the software runs its tests.
And finally, keep in mind that a soundcard will not tell you everything. It won't tell you if the output stage is oscillating for example (you pretty much need an oscilloscope for that).
The first step would be to chose a soundcard fitting your budget and available interface (usb, pci, pcie, etc). If you want to test DACs with balanced outputs and fairly high output levels, you'll probably want at least something like the focusrite 2i2.
Then you have to check that the DAC isn't a danger to the soundcard. Does it have offset ? What is its maximum output level ?
Then you have to pick a software to record and analyze what's going on. Among others, there are ARTA, RMAA, audiotester. Once your choice is made, you have to properly configure it. That's very software dependent so it's hard to be too detailed right now.
Then you simply connect your DAC to your recording soundcard input and let the software runs its tests.
And finally, keep in mind that a soundcard will not tell you everything. It won't tell you if the output stage is oscillating for example (you pretty much need an oscilloscope for that).
There are a couple of tricks you can use if your ADC distorts more than the DAC:
-Inserting a passive notch filter, for example a twin-T filter, that suppresses the fundamental. Make sure you use polystyrene, polypropylene or ceramic class 1 (like NP0 / C0G) capacitors (and if you should need any inductors, air cored ones), otherwise the filter might distort more than the DAC.
-Driving two DAC channels in antiphase with different amplitudes and making a weighted sum of the output signals using two resistors. As long as the distortion depends on the signal level, which it usually does, this nulls out the fundamental but not the harmonics.
These tricks make things more complicated, though, because you have to correct for how much the notch filter attenuates the harmonics / how much the weighted summing suppresses the n-th harmonic distortion.
-Inserting a passive notch filter, for example a twin-T filter, that suppresses the fundamental. Make sure you use polystyrene, polypropylene or ceramic class 1 (like NP0 / C0G) capacitors (and if you should need any inductors, air cored ones), otherwise the filter might distort more than the DAC.
-Driving two DAC channels in antiphase with different amplitudes and making a weighted sum of the output signals using two resistors. As long as the distortion depends on the signal level, which it usually does, this nulls out the fundamental but not the harmonics.
These tricks make things more complicated, though, because you have to correct for how much the notch filter attenuates the harmonics / how much the weighted summing suppresses the n-th harmonic distortion.
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Thanks servus
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The ARTA software has been successfully used with following soundcards:
RME Fireface UFX, UC, UCX, BabyFace Pro, Fireface 800, RME Fireface 400, RME HDSP
M-Audio Audiophile 2496, USB Transit, Mobile USB Pre, Firewire Solo
Axys D-AudioCard (mixer does not work on Windows 8/10)
Echo Gina24, Echo Layla 24, Echo Indigo I/O (notebook)
EMU 1820M, 1616M, 0204USB, 0404USB (*), EMU USB Tracker Pre (*)
Roland Quad and Duo Capture USB audio interfaces
Marian Trace Alpha, Terratec EWX 24/96 (*)
Focusrite Scarlett USB serie
Steinberg UR-22Mk2 USB audio interface
Digigram VxPocket 440 (*) - a notebook PCMCIA card
TASCAM US122L, US-2x2
Infrasonic Quartet, Sound Devices USBPre2
Creative Soundblaster X-Fi (works on all sampling frequencies in sound creation mode)
ESI Juli, U24 XL, ESI Quatafire 610, EgoSys Waveterminal 24
Creative Soundblaster Live 24 (*) and Extigy-USB (*), Audigy ZS laptop, but only at 48kHz sampling frequency,
Turtle Beach Pinnacle and Fuji (*)
Soundblaster MP3+ USB (notice: don't install SB driver, use a Windows default driver),
Soundcards and on-board audio with AC97 codecs,
* For this older cards driver does not work in Windows 7 / 8 / 10
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ARTA Requirements
I've got a Creative Soundblaster X-Fi around here and I think my old laptop has AC97!
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ARTA Software is classified as "shareware". To use it you have to pay for the user license key. If you have no license key, you can freely use this software only in a demo mode. The demo mode of programs is fully functional except loading and saving of files.
There are two types of licenses:
The personal license enables the single user personal use of the ARTA Software. The price for the personal license is 79 euros.
The commercial licence enables the institutional and multi-user use of the ARTA Software. The price for the commercial license is 149 euros.
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ARTA Download
Hmmm, not sure if that's on a budget ...
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