$500 USB cable

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.

Very informative post Al. Thanks.
Trying to better understand what you are saying in a couple of areas.
   
When you say USB communicates data via a differential pair of signals, and specifically regarding noise.

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.

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.

So do you mean that noise can be introduced into D/A circuits, only by un-reasonable (not normal?) circumstances?

If yes, can you give examples of this ?

thanks Chris

Hi Chris,

The two sentences you quoted are referring to two different things.

The first sentence refers to the likelihood that under normal circumstances the circuit receiving the data will not mistake a 1 for a 0, or vice versa, despite the presence of noise that may be conducted in the cable.

The second sentence refers to the possibility that noise that may be conducted in the cable may find its way into D/A converter circuitry, causing jitter, or into other circuitry further downstream (including analog circuitry), where it may have audible consequences even though the data has been received correctly. Conceivably it may "find its way" via unintended circuit paths such as stray capacitances, grounds which behave in a less than ideal manner at frequencies that are contained in the noise, by radiation of RFI (as Kijanki mentioned), etc. And that could very conceivably occur to an audibly significant degree under normal circumstances, depending on the specific designs that are involved. And that kind of effect is the only way I can think of by which sonic differences could occur between reasonably well designed USB cables, when used in reasonably well designed asynchronous USB applications.

When I was drafting my post it occurred to me that those two statements might be conflated, when they were meant to refer to different things. Which is why I added the words "when that determination is made" at the end of the following sentence, although perhaps I should have added clarification that was more explicit:

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.

Regards,
-- Al