• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Review and Measurements of SMSL X-USB Digital Audio Converter

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
12,455
Likes
4,274
Location
Seattle Area
#1
This is a review and measurements of the SMSL X-USB. It is a very small form factor USB to S/SPID, Toslink optical and I2S (using mini-HDMI connector). It is on kind loan from a member.

When I say small form factor, I mean it. Here is a comparison of it to a couple of DACs I have:

SMSL X-USB Picture.jpg


Even smaller is its display as you can (barely) see in the picture. Still, I like to have that than nothing.

Heavy cables are going to drag this around but maybe with the small size you can tape it to back or top of your DAC.

Retail price that I see as of this writing is around $89 plus shipping so close to $100.

The purpose of this product is to bring USB connectivity to older DACs without such an input. Alternatively if your DAC has a poor performing USB input, you can use these devices to improve their performance assuming they also have S/PDIF input.

Let's do some measurements and see how it does. As usual, if you are not familiar with what these graphs are, refer to my tutorial on understanding audio measurements: https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/

Measurements
Our weapon of choice here is the J-Test signal which brings out jitter and noise out of the DAC. For a DAC to test, I first started with Topping D50 but there was little difference of note there. So I tested with Schiit Uber 2 (review to come in the future). Here there were clear differences between the three devices under test.

First, let's see how the Schiit Modi 2 Uber does with its own USB interface and then driven via SMSL X-USB using its S/PDIF input:

SMSL X-USB with Schiit Modi 2 Uber.png


The "naked" Modi 2 Uber is in yellow. We see some spikes below 2 kHz which I happen to know comes out of my HP laptop USB bus. In addition there is random low frequency jitter which explains the broad "skirt" around our main 12 kHz tone in the source.

Addition of SMSL X-USB nicely cleans up the < 2 kHz spikes but unfortunately adds its own spikes a pair of which I have marked with the green cursor. While not an audible concern due to its low level, nevertheless it is not good engineering. Like there are oscillators running elsewhere in the device bleeding into the S/PDIF clock.

The Random jitter (in yellow) is left unchanged with indicates this is a problem in the DAC itself and not as a result of USB interface.

Next let's see what happens if we use my now ancient Audiophilleo USB to S/PDIF converter:

Audiophilleo with Schiit Modi 2 Uber.png


I say good engineering last and here is a great example of it. The Audiophilleo eliminates the low frequency noise and distortions from Modi 2 Uber without introducing any distortions of its own. It is a clear win over the SMSL X-USB.

I also made a comparison using the Gustard U-12 which I reviewed a while back:

Gustard U12 with Schiit Modi 2 Uber.png


As we see, the Gustart also does well matching Audiphilleo's performance while not introducing its own noise products.

Conclusions
The SMSL X-USB is small and attractively priced for a USB to S/PDIF converter. Alas, its performance is not satisfactory. Internal circuits leak noise onto the S/PDIF clock causing new distortion spikes while some cleaning of lower frequency USB noise is performed. Audibly these are benign so if you like the form factor and attractive price, it would make a decent purchase. Otherwise if you can spend a bit more and get the Gustard U12 ($169 including Amazon Prime shipping), it is a better performing unit.

As always, questions, comments, corrections, jokes, etc. are all welcome!
----
If you like this review, please consider donating funds for these types of hardware purchase using Patreon (https://www.patreon.com/audiosciencereview), or upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
12,455
Likes
4,274
Location
Seattle Area
#2
Oh, I forgot to mention that it works plug-and-play with Windows 10 Creator's edition with no driver install. It has the same USB interface as one of the Gustard DACs I had tested before.

It worked reliably with Roon.
 
Joined
Feb 16, 2018
Messages
28
Likes
15
#3
Well, the tease of the Modi2 Uber was interesting. Looks better than a Modi 2, but it's got that taper down to the noisefloor on the jitter tests still, just isn't as severe. Feels odd to see compared to so many other DACs that don't have that.
 

Jimster480

Senior Member
Patreon Donor
Joined
Jan 26, 2018
Messages
451
Likes
145
#4
Great review man!
The price of the xUSB has increased quite a bit since I originally purchased it, as it was around $45 when I got it. At a price of $100 its much less attractive. I wonder if SMSL is phasing this product out entirely as its stock is low on all sites I can find at the time of this writing.

Atleast it didn't do anything horrible to the audio and that was my main concern.

I'd like to see it against the Schiit Eitr though at $170, the Gustard U12 is actually the direct competitor there.
 

bunkbail

Member
Patreon Donor
Joined
Feb 27, 2018
Messages
43
Likes
16
#9
I had a Gustard U12 before and I thought it doesn't improve the SQ of my DAC (Audio-gd R2R-11), made it worse even. I then bought a similarly priced Schiit Eitr and it significantly improves the overall sonic performance of the DAC. If I live in the US I would have sent you the Eitr for review.
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
12,455
Likes
4,274
Location
Seattle Area
#13

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
1,897
Likes
746
Location
UK
#14
It's a symptom of digital audio's confusion and chaos that such a device should have a market.

If your DAC already has a USB input, and it is asynchronous, then it is already 'as good as it gets' because your output will be bit perfect. If the DAC's S/PDIF input works better than the USB, then something strange is going on because the S/PDIF interface requires either re-sampling, or for the DAC's sample clock to be adjusted in frequency now and again. i.e. the output isn't bit perfect.

If you need to get S/PDIF from USB, you are burdened with re-sampling when you don't have to be, so why not just buy a native USB DAC?

Any layman approaching the subject of digital audio must be utterly confused by all the little boxes that audiophiles clutter their lives with. The irony being that they could just plug their laptop into their amp from its headphone output and it might even work better than the little box approach. Are audiophiles masochists?
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
12,455
Likes
4,274
Location
Seattle Area
#15
If your DAC already has a USB input, and it is asynchronous, then it is already 'as good as it gets' because your output will be bit perfect. If the DAC's S/PDIF input works better than the USB, then something strange is going on because the S/PDIF interface requires either re-sampling, or for the DAC's sample clock to be adjusted in frequency now and again. i.e. the output isn't bit perfect.
There is a case where the USB input bleeds noise onto the DAC portion. As such, a different path may be cleaner as we see with Schiit Modi 2 Uber.

Fortunately more and more that is the exception than the norm.
 
Joined
Feb 9, 2018
Messages
23
Likes
15
#16
Yes, with my Opus 21 XS I have very old synchronous USB, not recommended, supporting 16/44.1 khz input. But with Allo DigiOne (similar like the one described but Ethernet to SPDIF) I can feed this old good DAC with 24/96 Khz. So it is young again. There is definitively market for such converters, maybe not for a long time, but there are still plenty of devices that handle SPDIF better then USB.
 

Blumlein 88

Major Contributor
Joined
Feb 23, 2016
Messages
3,526
Likes
1,636
#17
It's a symptom of digital audio's confusion and chaos that such a device should have a market.

If your DAC already has a USB input, and it is asynchronous, then it is already 'as good as it gets' because your output will be bit perfect. If the DAC's S/PDIF input works better than the USB, then something strange is going on because the S/PDIF interface requires either re-sampling, or for the DAC's sample clock to be adjusted in frequency now and again. i.e. the output isn't bit perfect.

If you need to get S/PDIF from USB, you are burdened with re-sampling when you don't have to be, so why not just buy a native USB DAC?

Any layman approaching the subject of digital audio must be utterly confused by all the little boxes that audiophiles clutter their lives with. The irony being that they could just plug their laptop into their amp from its headphone output and it might even work better than the little box approach. Are audiophiles masochists?
That is not quite correct. A device like this does not need any resampling. It will do re-clocking. The on-board asynch clock will generate a clock for the SPDIF output. The DAC SPDIF input will lock to that clock with a PLL or two. The PLL likely will not be as good as the clock of the device. But the correct bits will flow thru in bit perfect form.

A device like the subject of this review is not so much about improving jitter as allowing use of USB with DACs lacking a USB input. Yes, if your DAC has USB then simply use it.
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
1,897
Likes
746
Location
UK
#18
There is a case where the USB input bleeds noise onto the DAC portion. As such, a different path may be cleaner as we see with Schiit Modi 2 Uber.

Fortunately more and more that is the exception than the norm.
Why not just fix the USB problem..? Isolate the USB or whatever - or buy a better DAC, or use laptop headphone output! Instead of engineering, audiophiles just seem to cast around randomly.
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
1,897
Likes
746
Location
UK
#19
That is not quite correct. A device like this does not need any resampling. It will do re-clocking. The on-board asynch clock will generate a clock for the SPDIF output. The DAC SPDIF input will lock to that clock with a PLL or two. The PLL likely will not be as good as the clock of the device. But the correct bits will flow thru in bit perfect form.
If you look carefully, I wrote:

"... the S/PDIF interface requires either re-sampling, or for the DAC's sample clock to be adjusted in frequency now and again. "
 
Top Bottom