$500 USB cable

Digital coax cables are very different. In most cases D/A clock frequency is based on average frequency of the transfer while any time variations appear as jitter (noise in frequency domain). We can say that any S/Pdif cable (coax or Toslink) transfers the music (since timing is attached) while asynchronous USB transfers data. I hope you see the difference.

Jim Aud of Purist Audio Design

When thinking about a digital signal over USB, it can seem natural to think of it as a straightforward expression of 1's and 0's. However, it is more nuanced than that. Below a certain voltage, the signal says: "this is a 0." Above a certain voltage, it says "this is a 1." So, a 1 may be a 3.2 volt signal, and a 0 might be a 2.9. Since data transfer happens fast and often, it doesn't take much to skew a 1 to a 0, or a 0 to a 1. The digital signal isn't this series of neatly packaged squares, all labeled 1 or 0. They are in the ballpark, but they aren't completely uniform.

Any opinions on these statements from Jim Aud - Purist Audio Design ? 




  

My opinion is that Jim Aud and Purist Audio design cables are practically AND factually full of feces.
It does NOT matter weather they're 'completely uniform'
Completely or partially uniform 0 will still be 0.

The statement attributed to Mr. Aud does not reflect how a USB interface operates. First of all USB communicates data via a differential pair of signals, which greatly enhances noise immunity. The receiving circuitry just has to determine which of the two signals in the differential pair is at a higher voltage and which is at a lower voltage than the other, during each bit interval. And noise that is present on both signals (i.e., common mode noise) will be ignored under any reasonable circumstances, when that determination is made. Secondly, 1s and 0s are not distinguished from each other based even on that determination. They are distinguished based on whether or not there is a **change** in which signal is higher and which signal is lower, relative to what that relation was during the previous bit interval. There are other differences as well.

I don’t doubt that USB cables can make a difference in many applications, mainly as a result of coupling or radiation of noise into D/A converter circuitry or even analog circuitry further downstream, as alluded to by Kijanki and Williewonka. However, that does not mean that a $500 cable necessarily has any particular likelihood of outperforming a $50 cable or even a $10 cable in a given application. Also, I would disagree with any attribution of specific tonal or other sonic characteristics, such as warmth, to a particular USB cable. While making such attributions may often be appropriate in the context of analog cables, the sonic effects of electrical noise in a digital application will depend on the designs of the specific circuits that it may couple into, on the degree to which that coupling occurs at various circuit points, and on the specific spectral and other technical characteristics of the noise itself. Therefore any such effects can be expected to have little or no predictability, and little or no consistency from system to system.

Regards,
-- Al

Thank you Al marg for your input. Makes a lot of sense... and very educational.