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Review and Measurements of Asus STX II PCI Sound Card

amirm

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#1
This is a review and detailed measurements of Asus STX II PCI Express sound card. It is on kind loan from a member and retails for USD $219 on Amazon including Prime shipping. Full list price is $299.

This is a medium sized PC card which oddly requires external power. You can see it here together with the recently reviewed USB DAC, the Khadas Tone Board:

Asus STX II Sound Card Audio Review and Measurements.jpg


So inch for inch, it better measure a lot better. OK, some of that real estate is dedicated to headphone output and analog input which the Khadas board lacks. Still, with all the space, extra shielding, etc. it better do well. Asus specification shows near state of the art performance specs:

1540002500445.png


If it lives up to these specs, it would rate at tier just below state-of-the-art desktop DACs. Will it get there? Let's measure it and find out.

Edit: Turns out the ASIO interface with my AP software uses is stuck in 16 bit mode. Changing to 24 bit using external software, does remedy this and allows a few more dBs of performance. See later in the thread or this post: https://www.audiosciencereview.com/...f-asus-stx-ii-pci-sound-card.4915/post-111244

WASAPI interface is not impacted so if you use that, you get 24 bit support.

Measurements
The ASUS STX II allows "rolling" (swapping) of the current to voltage and output buffer op-amps. For this testing, I left the common buffer op-amp as shipped but swapped out one of the I/V op-amps to an LME49720. This way we kill two birds, testing the stock unit and effect of op-amp rolling to some extent. Here is our dashboard view:
Asus STX II Sound Card Audio Dashboard Measurements.png


Well, this is disappointing. Distortion specs are much worse than specified with SINAD being missed by whopping 13 dB!

Both output voltage and SINAD are better than my Gigabyte B8 motherboard though:
Asus STX II Sound Card Audio Sinad Measurements.png


On the other side of the coin, the Khadas Tone Board completely cleans its clock though with 110 dB of SINAD.

Let's test the claim of 124 dB for dynamic range:
Asus STX II Sound Card Audio Dynamic Range Measurements.png


Another massive miss. Here the Gigabyte B8 performs substantially better with 11 dB higher dynamic range.

The picture stays just as ugly with Jitter and noise:

Asus STX II Sound Card Audio Jitter and Noise Measurements.png


The J-test signal toggles all the sample bits to the tune of 250 Hz. This should be invisible since it is being applied to last bit of 24 bit words. Yet, we easily see its spectrum here indicating bleeding of digital circuits into analog.

Once again, the Gigabyte B8 motherboard did much better (inset).

Let's look at intermodulation distortion versus level:

Asus STX II Sound Card Audio Intermodulation Distortion Measurements.png


The higher noise level of Asus STX II hurts it here in the initial parts of the graph. Fortunately performance stays well behaved without the "hump" that the Gigabyte B8 demonstrates in mid-levels.

The Topping D50 also has a hump but it easily beats the Asus STX II in the rest of the spectrum.

Let's but not least, let's look at linearity:
Asus STX II Sound Card Audio Linearity Measurements.png


This is remarkably bad. And in both channels so differing op-amps in I/V state makes no difference. The error is off the charts by the time we get to the limit of 16 bit audio (96 dB). You lose accuracy in as low as 11 bits. Once gain, the Gigabyte B8 motherboard performs better and by large margin.

I did not test the headphone output. It has a 10 ohm output impedance which is a bit problematic.

Conclusions
My experience with add-on sound card has uniformly been poor. Despite claims of high measured performance, I would routinely hear my computer activity through them. Alas, I had not tested them for a while so went into this review thinking the situation may be much improved. That was not meant to be. The Asus STX II despite looking otherwise, has a number of serious engineering problems. At best we can say it is susceptible to differences in motherboards. But isn't that what they were supposed to do right for nearly $300? Make a card that would sound good regardless of the machine activity? Measured performance is far, far below specification and in a number of cases, worse than my motherboard.

Ultimately, my strong advice remains to spend your money on external DACs. USB interface is plenty fast, is plug-and play, and doesn't require opening the machine to use them. The ASUS STX II by the way, required custom drivers to work. Heaven forbid Microsoft changes its driver interface again and Asus doesn't provide an update for that future OS.

If you want a bare board solution, take a Khadas Tone Board, stick it inside your PC with a bit of sheet metal work and be golden for $99.

As always, questions, comments, corrections, etc. are welcome.

-----
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#3
interesting.... so looking at the SINAD alone - one would think it to be on par with the JDS Labs product, but looking at the rest of it... yikes. never would have guessed it to be a poor performer. in my mind I would have pegged it about on par with the JDS Labs DACS. What DAC chip does it use?
 

amirm

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#4
interesting.... so looking at the SINAD alone - one would think it to be on par with the JDS Labs product, but looking at the rest of it... yikes. never would have guessed it to be a poor performer. in my mind I would have pegged it about on par with the JDS Labs DACS. What DAC chip does it use?
It is a PCM1796

1540006815986.png
 

Sythrix

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#7
:facepalm:

I want my money back...

Thanks for testing it. I guess they couldn't solve the problems inherently present inside a computer case.
 
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#8
Can't say I'm surprised, audio has never been a main focus of Asus as far as I know. That's no excuse though.

I wonder how Creative Labs Sound Blaster products are today.
 
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#9
they have put out some pretty high end audio gear though in the asus essence one, essence stu and essence iii. you would think there would be a trickle down effect there. inside the pc may just be too much to overcome.
 
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#11
I don't think it has to do only with pc enviroment. I bet measuring a RME or Lynx card will be totally different.
When you see a card with external power supply, which is still from the pc psu, and swappable op amps, it means bullshit marketing.
 

Sythrix

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#12
If it's doing worse than Gigabyte's on-motherboard audio, the problems aren't "inherently present inside a computer case", this thing is just poorly engineered or the sample supplied to Amir is broken.
It's worse than the motherboard in some aspects, but not everything.

The problems inside of a computer could be numerous, and cannot simply be chalked up to the equivalent of the motherboard audio. It's running off a PCI-E slot, not meant for audio. It also requires a 4 pin molex connection probably straight off a noisy power supply, again not meant for audio. The motherboard, meanwhile, actually has an isolated PCB section for audio.

So yeah, I don't think they've overcome those limitations, which may very well have contributed to the bad measurements. Unless we get multiple tests across multiple systems, it's not like we'll be able to do anything but assume.
 
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#13
Atkinson had similar results from the first version of the card, but a bit better.

"With 16-bit data, the linearity-error test was dominated by the recorded dither noise, so I haven't shown the result. I couldn't replicate the manufacturer's claim of an A-weighted signal/noise ratio of 124dB for the Xonar Essence. However, ref. 1V output, I measured 114dB for the STX, which is still superb, but 102dB for the ST. It's possible that the actual ratio will depend on the computer in which the card is installed.
Read more at https://www.stereophile.com/content/asus-xonar-essence-ststx-soundcards-measurements
"
I wonder how he chooses what to show or not..
 
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Blumlein 88

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#14
Yes this is not good news. My last desktop using Gigabyte MB had decent on board sound with measurements 3 or 4 db less good than these without the nasty jitter profile. It did have terrible noise at 192 khz rates, but was good at 88 and 96 or less. My current desktop which is a home server has better on board sound. With similar numbers (roughly clean to 16 bits) and is clean at 192 khz. Neither let thru any audible or highly measurable computer activity into the output.

Clearly for someone on a budget a Behringer or Focusrite recording interface or some of the tested quality low cost external DACs are a much better place to spend money. Seems computer video, including built into the MB video is much better than on board or plug in card audio.

Come to think of it, the old Maudio Audiophile 96 sound cards would do about this good. First sound cards that had no computer bleedthru in my experience, though they weren't super quiet and did have very high jitter.

Maybe Asus can rebrand it a Schiit sound card, and pump up the price by $100.
 

soundArgument

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#17
I had the original Asus Xonar Essence STX, and I thought it sounded fine although, yes, the drivers sucked. I wonder if the sample measured is broken or defective.
 

Sythrix

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#18
I had the original Asus Xonar Essence STX, and I thought it sounded fine although, yes, the drivers sucked. I wonder if the sample measured is broken or defective.
I had the first as well and I remember it included printed measurements of your card (supposedly) in the box on a nice card. Perhaps QC has gone out the window. I was expecting the same level of care and attention to detail with the second one, but it was absent.
 
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#19
you do have to wonder how much each individual psu is going to affect things. pc psu quality can vary dramatically
 
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