There can be an argument there but the data doesn't support that. What we see instead is that USB by itself is cleaner than S/PDIF on the same DAC. And it is not just noise. Look at one of the other measurements: What we see in yellow are jitter spikes at regular frequencies when using S/PDIF input. The USB input (red) generates none of that. So clearly that is not in the USB signal or the PC source. What we are really seeing here is that manufacturers are doing a much more excellent job on USB than S/PDIF. They know it is a noisy signal and they have worked to clean it up. In the interest of fair reporting, I do have a USB DAC that is horrible in this regard (Schiit Modi 2). The answer there is not to polish the turd as the saying goes but to simply get a better DAC which need not cost more money at all. The other point here that is important is that we can measure all of this. No need to speculate blind. Noise measurements is one of the most common things in electronics. So before we promote any theory of problems, let's do that. Let's get data and only then say X and Y and Z. Not before.