Here is a little comparison of three different ways to convert USB to S/PDIF all driving an ultra low cost, $20 FiiO Taishan DAC. It is the only DAC on my workbench that takes S/PDIF input as the rest are all USB and I am too lazy to measure my main system 
.
A simple test tone at roughly 11Khz is output from the PC using Foobar2000. I had to use the Directshow filter as SIGNSTEK would not work otherwise. So all three are going through the kernel audio stack. Windows audio output format was selected to be 16-bit/44.1 Khz.
The first device measured is my Audiophilleo USB to S/PDIF converter/bridge. I bought this from Phil back in 2010/2011 when he had first started the company. It retailed for $500 which at the time was a very reasonable price since async USB was a rare bird.
The test tone is the near 0 db line on the left. In an ideal situation there would be nothing else after that. But this is not ideal and we have harmonics of that tone going up way high in frequency. Your amplifier and speakers may "hear" those tones but your ears would not. In the audio band of 20 to 20,000 Hz, there are no anomalies.
Note that we are testing the combination of DAC fidelity and S/PDIF input.
Next I add the measurement for SIGNSTEK Mini USB DAC which is only used as a USB to S/SPDIF converter (its DAC ignored). Here is what we get:
We see that SIGNSTEK has caused the DAC to have new distortion and noise products some of which are in the audible band (see the red spikes). The level though is at -100 db in the audio band though so it really is not an audible concern especially when we consider that this little device retails for $20 or so.
What we do see here is that bits are NOT bits. Two different digital inputs to the same DAC produce two different analog outputs.
Now let's use the S/PDIF output of the iFi iDAC2 DAC (again, ignoring its own internal DAC), driving the same Fiio Taishan:
Whoa! What happened here??? This $300 device is causing our little DAC to put out far more ultrasonic noise! It also has highly increased the amplitude of our harmonic distortion products!
Its saving grace over the SIGNSTEK is that its output in the audible band is just as clean as Audiophilleo. Still, this is not good engineering especially coming from a company that touts the quality of its products, says they have measurement gear, etc. Clearly it is spitting out lots of noise over its S/PDIF port that is polluting the FiiO DAC.
So there you have it. Well engineered products like Audiophilleo pass the test of time. Buy good stuff and it will last you. Go for hype without measurements and you get hit on the face like with the iFi.
Also this validates my saying that the best digital tweak is getting the best USB/SPDIF converter. It makes even low cost DACs perform better (measurably).
As always, I welcome correction, feedback and comments. Testing audio gear in spare time is always prone to errors and I am happy to correct anything that is found.
.A simple test tone at roughly 11Khz is output from the PC using Foobar2000. I had to use the Directshow filter as SIGNSTEK would not work otherwise. So all three are going through the kernel audio stack. Windows audio output format was selected to be 16-bit/44.1 Khz.
The first device measured is my Audiophilleo USB to S/PDIF converter/bridge. I bought this from Phil back in 2010/2011 when he had first started the company. It retailed for $500 which at the time was a very reasonable price since async USB was a rare bird.
The test tone is the near 0 db line on the left. In an ideal situation there would be nothing else after that. But this is not ideal and we have harmonics of that tone going up way high in frequency. Your amplifier and speakers may "hear" those tones but your ears would not. In the audio band of 20 to 20,000 Hz, there are no anomalies.
Note that we are testing the combination of DAC fidelity and S/PDIF input.
Next I add the measurement for SIGNSTEK Mini USB DAC which is only used as a USB to S/SPDIF converter (its DAC ignored). Here is what we get:
We see that SIGNSTEK has caused the DAC to have new distortion and noise products some of which are in the audible band (see the red spikes). The level though is at -100 db in the audio band though so it really is not an audible concern especially when we consider that this little device retails for $20 or so.
What we do see here is that bits are NOT bits. Two different digital inputs to the same DAC produce two different analog outputs.
Now let's use the S/PDIF output of the iFi iDAC2 DAC (again, ignoring its own internal DAC), driving the same Fiio Taishan:
Whoa! What happened here??? This $300 device is causing our little DAC to put out far more ultrasonic noise! It also has highly increased the amplitude of our harmonic distortion products!
Its saving grace over the SIGNSTEK is that its output in the audible band is just as clean as Audiophilleo. Still, this is not good engineering especially coming from a company that touts the quality of its products, says they have measurement gear, etc. Clearly it is spitting out lots of noise over its S/PDIF port that is polluting the FiiO DAC.
So there you have it. Well engineered products like Audiophilleo pass the test of time. Buy good stuff and it will last you. Go for hype without measurements and you get hit on the face like with the iFi.
Also this validates my saying that the best digital tweak is getting the best USB/SPDIF converter. It makes even low cost DACs perform better (measurably).
As always, I welcome correction, feedback and comments. Testing audio gear in spare time is always prone to errors and I am happy to correct anything that is found.
