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Review and Measurements of SMSL X-USB Digital Audio Converter

Jimster480

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#21
@amirm I was just thinking, you could test the xUSB against the DX7 & DX7S themselves as they both offer Coaxial output too.
And then test with the D10 when it arrives as it also doubles as a USB->Coax Adapter.
 

Jimster480

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#23
Yes I can wait, I just was thinking about other things to test here to make the measurements more complete. I've used the Coax output on my DX7 so I'm interested haha
 
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#24
First glanced at the picture and for a minute thought it is:-

ADI-Pro vs D7s

... or is this teaser to what’s to come?

(get pop-corn)
 

amirm

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#25
ADI-Pro vs D7s

... or is this teaser to what’s to come?

(get pop-corn)
Yes and I will probably throw in the Exasound E32 in the mix too.
 
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#27
"I first started with Topping D50 but there was little difference of note there." Are you saying that with better Dacs (eg D50 or possibly Chord Mojo etc) then the device works essentially perfectly? If so I'm guessing this is due to better DACs reclocking the optical signal..?
I'm very interested to see how the Topping D10 compares to this unit as a USB to optical converter, will you be testing this?
 

Blumlein 88

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#30
Sorry, should have made my question a bit more clear: Does the X-USB + D50 still show the jitter? Or is it reclocked out?
Not Amir, but maybe I can answer.

The X-USB has its own clock for the outgoing SPDIF signal. That will go toward the D50. So the D50 will lock to that with a PLL with a good chance most of the jitter is part of the PLL.

Amir is saying better DACs that include USB will have a good implementation and since they will use a local clock to do the conversion it will have less jitter than going thru a converter like this and into another DAC.

So specifically, using the X-USB to feed the D50 is going to have more jitter than simply feeding USB to the D50 itself. Incidentally this will be true even with reclockers, because no matter how well the signal is reclocked using a PLL to lock onto an external signal has more jitter than a crystal clocking the data locally.
 
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#31
Not Amir, but maybe I can answer.

The X-USB has its own clock for the outgoing SPDIF signal. That will go toward the D50. So the D50 will lock to that with a PLL with a good chance most of the jitter is part of the PLL.

Amir is saying better DACs that include USB will have a good implementation and since they will use a local clock to do the conversion it will have less jitter than going thru a converter like this and into another DAC.

So specifically, using the X-USB to feed the D50 is going to have more jitter than simply feeding USB to the D50 itself. Incidentally this will be true even with reclockers, because no matter how well the signal is reclocked using a PLL to lock onto an external signal has more jitter than a crystal clocking the data locally.
Thanks, that was kind of my understanding of it, but what I thought Amir was saying here:
"I first started with Topping D50 but there was little difference of note there. So I tested with Schiit Uber 2. Here there were clear differences between the three devices under test."
Made me think that the D50 was somehow correcting the X-USB jitter(?).
The reason I'm interested in devices like the X-USB (and it seems the D10 does USB to optical conversion too) is that using optical, they have the benefit of isolating the dac/amp from the potentially noisy laptop.
 

Blumlein 88

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#32
Thanks, that was kind of my understanding of it, but what I thought Amir was saying here:
"I first started with Topping D50 but there was little difference of note there. So I tested with Schiit Uber 2. Here there were clear differences between the three devices under test."
Made me think that the D50 was somehow correcting the X-USB jitter(?).
The reason I'm interested in devices like the X-USB (and it seems the D10 does USB to optical conversion too) is that using optical, they have the benefit of isolating the dac/amp from the potentially noisy laptop.
Most DACs not named Schiit don't have a problem with noise from the computer. It doesn't hurt to go optical though.
 

amirm

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#34
OK, here is the test with D50. Seems like my memory was faulty as there is a difference:

Topping D50 with and without SMSL X-USB Jitter Measurement.png


The increased noise components persisted when using Toslink.

To see if that is created by X-USB or Topping D50, I tested the latter using my Audio Precision analyzer S/PDIF output and same noise was there.

In other words, the X-USB is as good as the usb interface inside D50. It is just that there is extra noise when S/PDIF is used in Topping D50 relative to its USB input, showing once again that async USB is a superior interface to S/PDIF.

Fortunately the levels of new distortion spikes over S/PDIF are close to -130 dB down so absolutely not an audible concern.

Bottom line is what is stated: if you have a good USB interface, use that instead of buying X-USB. It can't do better and might do a bit worse (measurable, but not audibly).
 

Blumlein 88

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#35
Optical usually has more jitter vs USB though, as long as the implementation is clean.
While that was once true, it often (perhaps usually) isn't true anymore. Poor optical converter parts were the problem way back when. Here a Vlink USB to SPDIF converter. One graph is via coax cable and one via optical cable. The small spikes to the side are in the DAC itself with whatever is used. As you can see no difference in Toslink vs coax. This is a zoomed in view between 10 khz and 14 khz.

Optical vlink vs coax.png
 
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#36
Thanks Amir.
I guess I'm still a bit confused as to where exactly the jitter in either the Modi2 or the D50 readings is really coming from:
If the <1k noise on the D50 reading is being generated by the X-USB, why is it not visible on the Modi2 reading?
If the 7k noise on the Modi2 reading being generated by the X-USB, why is it not visible on the D50 reading?
 

amirm

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#37
If the <1k noise on the D50 reading is being generated by the X-USB, why is it not visible on the Modi2 reading?
It is not. That jitter is inherent in the S/PDIF interface of D50 since it shows up with my Audio Precision as input.

If the 7k noise on the Modi2 reading being generated by the X-USB, why is it not visible on the D50 reading?
Two possibilities:

1. The D50 has better high-frequency filtering of noise over S/PDIF.

2. The Modi 2 S/PDIF has extra noise there relative to its USB in which case it is the guilty party vs X-USB. :)
 

amirm

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#38
OK, here is the test with D50. Seems like my memory was faulty as there is a difference:

View attachment 11429

The increased noise components persisted when using Toslink.

To see if that is created by X-USB or Topping D50, I tested the latter using my Audio Precision analyzer S/PDIF output and same noise was there.
Ah, I found the cause of those extra spikes: they are due to the activities of the front panel on D50! I was doing some other testing and noticed that the same noise popped up and then went off. It was synchronous with the display timing out and shutting off. So there is really no issue here with the S/PDIF input or SMSL X-USB. Just something for D50 owners to be aware of.
 

Jimster480

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#39
Ah, I found the cause of those extra spikes: they are due to the activities of the front panel on D50! I was doing some other testing and noticed that the same noise popped up and then went off. It was synchronous with the display timing out and shutting off. So there is really no issue here with the S/PDIF input or SMSL X-USB. Just something for D50 owners to be aware of.
So does this change your initial measurements?
 

amirm

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#40
So does this change your initial measurements?
You mean for D50? If so, no. It has a nice auto-on, auto-off display so once the music starts playing it shuts off and the noise goes away.
 
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