Three USB to S/SPDIF Converter Measurements: Audiophilleo, iFi iDAC2, SIGNSTEK

[DonH56]

Note using exact sub-multiples of the sampling frequency causes multiple spur frequencies to fall into the same FFT bin... Picking frequencies relatively prime, or just odd multiples, will help prevent that. So, choosing 11.05 kHz instead of 11.25 kHz can be a good thing.

 

[amirm]

Note using exact sub-multiples of the sampling frequency causes multiple spur frequencies to fall into the same FFT bin... Picking frequencies relatively prime, or just odd multiples, will help prevent that. So, choosing 11.05 kHz instead of 11.25 kHz can be a good thing.

That's right. It was not a bug but a feature!

Thanks Don.

 

[amirm]

Here is an overlay of the Tact AP2 in red and Vlink in blue playing 11,025 hz tone. This is a snapshot of realtime FFT so the little peaks bounce around 3 db or so. The small differences you see fluctuate, but amount to nothing.

I too tested the TacT and found it distinctly different than all the other DACs and processors I measured. Here is the result with Audiophilleo as you and Berkeley Alpha USB:

Berkeley is in yellow and Audiophilleo in red. Notice how the Berkeley does better around the main tone with far less spikes and fewer of them than Audiophilleo. This seemed specific to TacT.

Ultimately these measurements will vary with the driving PC and DAC in use. But your conclusion is correct that there is no audible consequence.

 

[DonH56]

That's right. It was not a bug but a feature!

Thanks Don.

I must say that the urge to make a Microsoft OS-related comment in response to that was almost overwhelming...

Awesome series of measurements and such, BTW. Is there a way to like the whole thread?

 

[Blumlein 88]

I too tested the TacT and found it distinctly different than all the other DACs and processors I measured. Here is the result with Audiophilleo as you and Berkeley Alpha USB:

View attachment 5560

Berkeley is in yellow and Audiophilleo in red. Notice how the Berkeley does better around the main tone with far less spikes and fewer of them than Audiophilleo. This seemed specific to TacT.

Ultimately these measurements will vary with the driving PC and DAC in use. But your conclusion is correct that there is no audible consequence.

I assume you know that 93.9 is actually unity gain on the Tact. More than that involves digital gain and odd results.

 

[amirm]

I assume you know that 93.9 is actually unity gain on the Tact. More than that involves digital gain and odd results.

The digital input samples don't change there so assuming their volume control is causal, then that should not be a factor. What changes the output is the level of isolation between the digital input and what the DAC produces.

 

[RayDunzl]

The digital input samples don't change there so assuming their volume control is causal, then that should not be a factor. What changes the output is the level of isolation between the digital input and what the DAC produces.

Not sure what you said there. The volume control only changes level in the analog domain?

Atkinson found "clipping" in his measurements, if this is the same device.

http://www.stereophile.com/roomtreatments/437/index.html

 

[amirm]

Not sure what you said there. The volume control only changes level in the analog domain?

Sorry . In DSP lingo "causal" means a stable processing method that does not rely on past behavior for current. In that manner makes the system a black box independent of previous input and hence, we can compare two methods of digital inputs without worrying about what the black box might do differently for each one.

 

[RayDunzl]

In DSP lingo "causal" means a stable processing method that does not rely on past behavior for current. In that manner makes the system a black box independent of previous input and hence, we can compare two methods of digital inputs without worrying about what the black box might do differently for each one.

Well...

Not sure what you said there either that has to do with a volume control that seems to be able to cause digital clipping by manipulating digital levels and not analog voltages.

I have one or two in my digital chain (not in my main DAC though).

 

[amirm]

Well...

Not sure what you said there either that has to do with a volume control that seems to be able to cause digital clipping by manipulating digital levels and not analog voltages.

I am saying it doesn't matter how it works. The only change I am making is the digital input and what came out was very different differences than with other DACs.

 

[RayDunzl]

it doesn't matter how it works

Oh.

Ok, I understand now.

 

[Blumlein 88]

I am saying it doesn't matter how it works. The only change I am making is the digital input and what came out was very different differences than with other DACs.

Well, it will matter. I suspect the analog output is being slightly overdriven when a high level signal and digital gain is applied. If you were using the digital gain for a signal low in level it wouldn't matter. I have measured that you get a spray of low level grunge that looks like IMD when you combine high signal level with settings over 93.9 on the volume. It could be some other aspect of how the gain is being done as well and maybe it is some aliasing cropping up, but the filter in my white noise plot looks pretty steep.

In any case, if the analog circuit is reaching some point of non-linearity it might react to different digital feeds oddly. You can see in some of the plots I posted it acts nearly identical to another DAC, and I did everything with volume on 93.9. If it isn't much bother might be worth repeating at least one combination with lowered volume on the Tact. I ran into this years ago doing some comparisons of different digital feeds. Results were odd. When I dropped volume it simply went away. Even .1 db up and you can find the grunge starting to stick out of the noise floor.

 

[amirm]

Well you might as well test as you already have them. That's why I sent the stuff . It's only been a year now Might as well just add the same measurements of the SPDIF converter to this thread.

OK, here it is. The unit Mike sent me is the Melodious-Audio MX-U8. It retails for $270 on Amazon: https://www.amazon.com/Melodious-Ultimate-Digital-Interface-Ver-1-7/dp/B01CHXYAV2

It is a hefty little box:

I tested it with the same FiiO Taishan $20 DAC and compared the results to the best we had so far which was the Audiophilleo:

The result was identical performance with the two graphs right on top of each other. This says that this is a high quality implementation and that we are now limited by the performance of the FiiO Taishan DAC than the S/PDIF input to it.

Note that installation was a bit tricky. They just dump you in a folder with two versions of XMOS drivers. I tried the newer version and the installation would fail at the end. Then tried the older version that was also on the site and it worked.

Wanted to compare all of this to my Berkeley Alpha USB but unfortunately I can't get it to work on my laptop anymore . It completely screws up the audio samples on the way out. Maybe doesn't work well with Dshow interface anymore. Will mess with it later.

Thanks Mike for sending this to me.

 

[RayDunzl]

What sample rates were tested?

 

[amirm]

What sample rates were tested?

The same: 44.1.

 

[RayDunzl]

48kHz showed problems earlier in the other thread where the DAC functions were examined.

 

[amirm]

48kHz showed problems earlier in the thread.

Not in this thread. It was the DAC review thread where 48 Khz showed problem. For that reason for these tests I avoided that sampling rate.

 

[RayDunzl]

It was the DAC review thread where 48 Khz showed problem. For that reason for these tests I avoided that sampling rate.

That doesn't make sense to me.

 

[amirm]

That doesn't make sense to me.

I am saying I only tested the difference USB to S/PDIF converters using 44.1 Khz into the FiiO DAC. I did not test these at 48 Khz because the DAC has its own problems there.

 

[RayDunzl]

Ok, now I understand the rationale, sort of.

But why test USB->S/PDIF using a superior analyzer and an inferior DAC ?