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Swissonic Converter AD 24/192 (ADC) Measurements

dominikz

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#1
After the recent measurement I did for the unbranded ADC I got off eBay, to compare a friend borrowed me a relatively similar device by a thomann.de house brand - Swissonic Converter AD 24/192 that sells for about 40€:
20210613_201731.jpg
20210613_201720.jpg

Basic features are mostly the same, except this one comes with a power button, a dedicated 9V PSU and boasts 24bit/192kHz sample rate conversion support. Visually it is more appealing to me, albeit a bit bigger than the unbranded ADC I tested previously. Let's have a look at how it performs. :)

The measurements you'll see next were done with the RME Babyface soundcard, first generation - measured here. The ADC was connected to optical SPDIF input of RME Babyface, clock source was the optical input (i.e. ADC) and the sample rate was 192kHz (native sample rate of ADC), though I also did a few tests at 48kHz to see how it behaves after resampling in the receiving device. Unbalanced/headphone output of RME babyface was used as the signal generator.

NOTE: One thing I noticed right away is that the device seems to have flipped left and right channels :confused: - i.e. the analogue channel marked as 'R' is sent as left channel over digital, and vice-versa. So the measurements you're about to see were done with the analogue connection flipped, to get correct L/R channel mapping.

Again, I'll start with RMAA summary at 192kHz sample rate (MME driver, input level set to recommended -1 dBFS by reducing RME output level by ~2dB):
1623609194531.png

Although far from state of the art, we can see right away it performs much better than the unbranded, cheaper device: flatter FR, ~10 dB better noise and dynamic range (approximately hits 16 bit range), an order of magnitude lower THD and IMD, THD+N/SINAD better by more than 20dB, and crosstalk by more than 40dB!

It is interesting that the right channel shows a lot better noise performance than the left one:
1623610795745.png


At 48kHz the results are mostly comparable, main issue being that noise level goes up by about 10dB:
1623609627044.png



Here's the frequency response at 192kHz vs 48kHz:
Swissonic Converter AD 24-192 - frequency response 192kHz vs 48kHz.png

As we can see, the channels match each other nicely and the FR is flat and uneventful - as it should be :) There is no significant LF loss in audible band this ADC - it is actually even less than in my RME soundcard ADC:
FR compare.png

The one strange thing that shows up in both RMAA and REW measurement is different behaviour of the filter between channels at 48kHz sample rate - we see the left channel has a nice and sharp filter, while the right one seems to lack it and just shows a blip before the Fs/2 frequency - TBH I'm not sure why is that.

Next let's see the spectrum of a 1 kHz sine at -1 dBFS peak at Fs=192kHz:
Swissonic Converter AD 24-192 1kHz tone at -1 dBFS peak 192kHz sampling rate.png

Distortion is dominated by the 2nd harmonic, but the spectrum is reasonably clean otherwise. We see noise-shaping in the extreme HF.
48kHz shows slightly elevated noise level, but otherwise similar:
Swissonic Converter AD 24-192 1kHz tone at -1 dBFS peak 48kHz sampling rate.png


Let's look now at the THD vs level sweep at 1kHz:
Swissonic Converter AD 24-192 - THD vs level.png

As we see, compared to the unbranded ADC this one achieves lower absolute THD figures (minimum is around 0.002% / -94dB around 0,2Vrms / -17dBFS RMS input level), and can handle more input voltage - clipping onset is ~1,5Vrms / ~5,7 dBu. Again we can see a bit better performance in the right channel vs left.

Lastly let's look at the THD vs frequency at two input levels at 192kHz, first at 0,1 Vrms input (-26,4 dBFS RMS), left ch:
Swissonic Converter AD 24-192 - left ch THD at 0.1V input (192kHz).png

And then at 1 Vrms (-6,4dBFS RMS):
Swissonic Converter AD 24-192 - left ch THD at 1V input (192kHz).png
At 48kHz sample rate, 1Vrms input - not much surprise here:
Swissonic Converter AD 24-192 - left ch THD at 1V input (48kHz).png

As we can see from these and previous measurements (THD vs level), above 0,2-0,3 Vrms input the 2nd harmonic becomes the dominating factor of THD.

In summary, this ADC seems to perform much better, and though not state of the art, it should IMO be transparent when used to digitize low dynamic range sources like turntables and such - I quickly tested it with mine and thought it worked just fine :) Flipped channels are an issue, of course, but I don't know if all units have it - be sure to check if you have this device and connect the cables accordingly.
 
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