This is a review and detailed measurements of the Matrix Audio X-SPDIF 2 USB to S/PDIF and I²S (IIS) converter. It is on kind loan from member who also sent me the Wyred4Sound DAC-2v2 SE DAC. The X-SPDIF 2 costs USD $379 but the company is selling for reduced cost of USD $341.10. Some complicated math must have gone into that computation to come up with that extra 10 cents in the price! 
The S-XSPDIF 2 comes in a small but very heavy enclosure. You can see it almost lost in the pool of gear I had to use to test its capabilities:
It is the non-descript box on top of the Wyred4Sound DAC. To the right, is the Wyred4Sound PS-1 multi-voltage power supply. It has modules you buy that give you different output voltages. The owner supplied that so I tested with and without it as the X SPDIF-2 can run on USB power alone. The PS-1 costs $399 for a single output voltage. Each extra output costs an extra $125. In other words, in base configuration with a single output, it will cost you more than the Matrix Audio X-SPDIF 2 converter!
In addition to S/PDIF output, the X SPDIF-2 can also output I²S interface. It does this as commonly done using an HDMI connector and cable. Note that this has nothing to do with HDMI interface. They are simply using the connector and cable because it can carry high-speed signals and is cheap due to its mass usage. The owner was interested to know if the I²S interface works any better than S/PDIF with the Wyred4Sound DAC, hence the combo.
Let's get started with measurements and see what we have.
Measurements
I am still refining my measurements here so please excuse the continued changes in settings and graphs used. Also, we are measuring such small signals that I don't yet trust repeatability of them. So for this review, I have re-run all the measurements again so don't try to compare them verbatim to previous tests/reviews.
Fort the first test, I thought I address owner's need directly which is to see if there is a difference in Wyred4Sound DAC-2v2 SE DAC when using its own USB input, versus either S/PDIF or I²S. Here is the output using our jitter test:
There is absolutely no difference! All three interfaces produce the same analog output. You know, the thing that hits your ears.
Now, there may be differences there but they are hidden in rather high jitter spectrum of Wyred4Sound DAC V2SE. It is the "weak link" as they say. This was a disappointment as I could no longer test using this DAC and had to resort to Topping D50. Unfortunately I no longer have a DAC with I²S interface so this is the end of the road for that analysis.
My Audio Precision APx555 can analyze jitter by itself. It extracts it from the S/PDIF stream and can then perform analysis on it as if it were audio signal. As such we can run our FFT analysis and see what we find as far as the spectrum when feeding the devices the "J-test" signal. J-test at 48 kHz sampling which I tested is a 12 kHz square wave with an embedded one-bit toggling 250 Hz square wave. DACs normally filter all but the primary tone converting it to a single tone as you see in the DAC measurement above. The 250 Hz toggle is playing with the rightmost bit of a 24-bit signal so should not be measurable. If it is, it shows that the device is sensitive to digital input stream. I know, a lot of technical concepts here but thought I explain it. If you don't understand it, stay with me and we can still make sense out of the data.
As a baseline, I thought we should see how good the S/PDIF digital output is out of the APx555 Audio Analyzer. Here is its jitter spectrum:
The spectrum is mostly noise-like but we have a few spikes are that correlated with our 12 kHz square wave causing spikes in jitter at some multiples of it. Worst case amplitude is only 8 picoseconds though so don't get excited over this being an audible issue.
Note again that what is being measured is a digital signal. No DAC is in the loop. The APx555 captures a digital pulse train and extract the variations out of it (jitter).
Next, let's analyze what is coming out of the Matrix Audio S/PDIF output when being driven naturally by the computer using its USB port for data and power:
We now have a lot more spikes there as compared to our APx555 which is comforting to me seeing how the APx555 retails for $28,000. There are finely spaced spikes around the larger spikes which I am assuming are the components of the 250 Hz sub-square wave in j-test. It could also be mains related power supply spikes.
Now let's juice up the X SPDIF-2 with Wyred4Sound PS-1 power supply. You would think it would make things better, right?
Wrong! If you look to the left, we see that the low frequency spikes have increased and with it, we now have a lot more of them further down the spectrum.
Reason is simple: yet another power supply, yet another source of ground loop, mains leakage. That low level "hum" rides inside the X SPDIF-2 converter, modulating clocks and such. But again, we are talking very small signals here with worst case being 18 picoseconds. So don't go asking, "how come I don't hear it." You are not going to hear, but we sure as heck can measure it.
Let's now compare the Matrix Audio X SPDIF-2 to our budget recommendation DAC and USB to S/PDIF converter, the Topping D10 (USD $90 including shipping):
Lot more spikes are visible now and some peaks up to 40 picoseconds or so. This may seem to be bad thing but it might be reverse of that: the peaks are so close to each other that may resemble noise than individually identifiable spikes. But again, all of this is at such low levels that I don't think either will be audible. Still, the Matrix Audio X SPDIF-2 shows that it can technically do better.
Now let's have a real-life scenario driving the Topping D50 DAC. To start, let's compare Audio Precision APx555 driving it versus Matrix Audio X SPDIF-2 converter:
Here we see a series of spikes with the APx555 analyzer which are clearly created due to mains frequencies. The Topping D50 is powered by yet another switching power supply (one from a Samsung mobile phone) so naturally we see mains leakage there. The Matrix Audio X SPDIF-2 doesn't create nearly as much of that by itself. But power it with a PS-1 external power supply and it inherits the same problem:
Finally, let's drive the Topping D50 with D10 as a USB to S/PDIF converter:
So we get our power supply noise spikes again although probably a bit more elevated than when APx555 was driving the D50.
Conclusions
It is so easy to imagine scenarios for improvement audio performance based on what "makes sense" to one's mind. Unfortunately these are complex technologies and don't yield themselves to lay assumptions. To wit, we easily saw that the addition of Wyred4Sound PS-1 power supply did nothing for baseline performance and just served to create extra ground loops. Seeing how the the PS-1 lacks any regulator certification, it is easy to say don't spend your money there.
As for Matrix Audio X SPDIF-2 converter, it seems to do its job. Can't match the quality of my audio analyzer but in real life with a DAC, it actually seemed to do better (this may very well be a DAC thing). So from engineering point of view, assuming you don't add an external power supply to it, I don't have any issue with someone purchasing it. The price is actually "reasonable" give how much custom designed logic is in there.
Personally I would just use the Topping D10. It has a nice display telling you the sample rate, has a bonus DAC included for one fourth the price of Matrix Audio X SPDIF-2 converter.
As for I²S, we got bamboozled by Wyred4Sound DAC-2V-SE being the dominant noise and jitter source. I will have to do the comparison at a later date when I have a more performant DAC.
Finally, please note that we are seriously "measurebating here." I have to zoom in so much into performance of these signals that breathing on them may change things. So do not worry about any audibility issues here. Use USB if that comes with your DAC and be done with it. Don't string all these things together thinking you are doing something useful.
------------
As always, questions, comments, recommendations, etc. are welcome.
It is snowing here for the first time this year. I need some money to buy snowshoes. Yes, it is only one inch of snow but you don't want me to fall and get hurt, do you? So please consider donating money 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).
The S-XSPDIF 2 comes in a small but very heavy enclosure. You can see it almost lost in the pool of gear I had to use to test its capabilities:
In addition to S/PDIF output, the X SPDIF-2 can also output I²S interface. It does this as commonly done using an HDMI connector and cable. Note that this has nothing to do with HDMI interface. They are simply using the connector and cable because it can carry high-speed signals and is cheap due to its mass usage. The owner was interested to know if the I²S interface works any better than S/PDIF with the Wyred4Sound DAC, hence the combo.
Let's get started with measurements and see what we have.
Measurements
I am still refining my measurements here so please excuse the continued changes in settings and graphs used. Also, we are measuring such small signals that I don't yet trust repeatability of them. So for this review, I have re-run all the measurements again so don't try to compare them verbatim to previous tests/reviews.
Fort the first test, I thought I address owner's need directly which is to see if there is a difference in Wyred4Sound DAC-2v2 SE DAC when using its own USB input, versus either S/PDIF or I²S. Here is the output using our jitter test:
There is absolutely no difference! All three interfaces produce the same analog output. You know, the thing that hits your ears.
Now, there may be differences there but they are hidden in rather high jitter spectrum of Wyred4Sound DAC V2SE. It is the "weak link" as they say. This was a disappointment as I could no longer test using this DAC and had to resort to Topping D50. Unfortunately I no longer have a DAC with I²S interface so this is the end of the road for that analysis.
My Audio Precision APx555 can analyze jitter by itself. It extracts it from the S/PDIF stream and can then perform analysis on it as if it were audio signal. As such we can run our FFT analysis and see what we find as far as the spectrum when feeding the devices the "J-test" signal. J-test at 48 kHz sampling which I tested is a 12 kHz square wave with an embedded one-bit toggling 250 Hz square wave. DACs normally filter all but the primary tone converting it to a single tone as you see in the DAC measurement above. The 250 Hz toggle is playing with the rightmost bit of a 24-bit signal so should not be measurable. If it is, it shows that the device is sensitive to digital input stream. I know, a lot of technical concepts here but thought I explain it. If you don't understand it, stay with me and we can still make sense out of the data.
As a baseline, I thought we should see how good the S/PDIF digital output is out of the APx555 Audio Analyzer. Here is its jitter spectrum:
The spectrum is mostly noise-like but we have a few spikes are that correlated with our 12 kHz square wave causing spikes in jitter at some multiples of it. Worst case amplitude is only 8 picoseconds though so don't get excited over this being an audible issue.
Note again that what is being measured is a digital signal. No DAC is in the loop. The APx555 captures a digital pulse train and extract the variations out of it (jitter).
Next, let's analyze what is coming out of the Matrix Audio S/PDIF output when being driven naturally by the computer using its USB port for data and power:
We now have a lot more spikes there as compared to our APx555 which is comforting to me seeing how the APx555 retails for $28,000.
There are finely spaced spikes around the larger spikes which I am assuming are the components of the 250 Hz sub-square wave in j-test. It could also be mains related power supply spikes.Now let's juice up the X SPDIF-2 with Wyred4Sound PS-1 power supply. You would think it would make things better, right?
Wrong! If you look to the left, we see that the low frequency spikes have increased and with it, we now have a lot more of them further down the spectrum.
Reason is simple: yet another power supply, yet another source of ground loop, mains leakage. That low level "hum" rides inside the X SPDIF-2 converter, modulating clocks and such. But again, we are talking very small signals here with worst case being 18 picoseconds. So don't go asking, "how come I don't hear it." You are not going to hear, but we sure as heck can measure it.
Let's now compare the Matrix Audio X SPDIF-2 to our budget recommendation DAC and USB to S/PDIF converter, the Topping D10 (USD $90 including shipping):
Lot more spikes are visible now and some peaks up to 40 picoseconds or so. This may seem to be bad thing but it might be reverse of that: the peaks are so close to each other that may resemble noise than individually identifiable spikes. But again, all of this is at such low levels that I don't think either will be audible. Still, the Matrix Audio X SPDIF-2 shows that it can technically do better.
Now let's have a real-life scenario driving the Topping D50 DAC. To start, let's compare Audio Precision APx555 driving it versus Matrix Audio X SPDIF-2 converter:
Here we see a series of spikes with the APx555 analyzer which are clearly created due to mains frequencies. The Topping D50 is powered by yet another switching power supply (one from a Samsung mobile phone) so naturally we see mains leakage there. The Matrix Audio X SPDIF-2 doesn't create nearly as much of that by itself. But power it with a PS-1 external power supply and it inherits the same problem:
Finally, let's drive the Topping D50 with D10 as a USB to S/PDIF converter:
So we get our power supply noise spikes again although probably a bit more elevated than when APx555 was driving the D50.
Conclusions
It is so easy to imagine scenarios for improvement audio performance based on what "makes sense" to one's mind. Unfortunately these are complex technologies and don't yield themselves to lay assumptions. To wit, we easily saw that the addition of Wyred4Sound PS-1 power supply did nothing for baseline performance and just served to create extra ground loops. Seeing how the the PS-1 lacks any regulator certification, it is easy to say don't spend your money there.
As for Matrix Audio X SPDIF-2 converter, it seems to do its job. Can't match the quality of my audio analyzer but in real life with a DAC, it actually seemed to do better (this may very well be a DAC thing). So from engineering point of view, assuming you don't add an external power supply to it, I don't have any issue with someone purchasing it. The price is actually "reasonable" give how much custom designed logic is in there.
Personally I would just use the Topping D10. It has a nice display telling you the sample rate, has a bonus DAC included for one fourth the price of Matrix Audio X SPDIF-2 converter.
As for I²S, we got bamboozled by Wyred4Sound DAC-2V-SE being the dominant noise and jitter source. I will have to do the comparison at a later date when I have a more performant DAC.
Finally, please note that we are seriously "measurebating here." I have to zoom in so much into performance of these signals that breathing on them may change things. So do not worry about any audibility issues here. Use USB if that comes with your DAC and be done with it. Don't string all these things together thinking you are doing something useful.
------------
As always, questions, comments, recommendations, etc. are welcome.
It is snowing here for the first time this year. I need some money to buy snowshoes. Yes, it is only one inch of snow but you don't want me to fall and get hurt, do you? So please consider donating money 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).
Last edited:
