$500 USB cable

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

Thanks Al

Have heard/read the "0 - 1" process explained numerous times, but not as good as you did. Interesting what one can read in the audio online glossies. The article that statement came from was only a year old.

I did a lot of research before I bought the DAC I use. As an old school computer guy, the fact that it advertised USB design, with performance that equalled S/PDIF was a big selling feature to me. It has lived up to its claim.

Been part of the IT industry my whole adult life. Still remember using the IBM 360-370, Amdahl, Tandem etc... mainframes and all those reel tapes. :^)

Cheers Chris

People assign analog attributes to digital cables. Warmer, colder, brighter etc. I just wonder which bits are added, changed, or entirely missed when the sound turns warmer or brighter etc.? If bits are missed or added it will likely cause nasty noises (if not corrected by the error correction mechanism of the receiving end). Try to transfer a high-resolution camera picture via a reasonable quality ($15) USB cable and observe the resulting picture. Do you see any distortion? Hardly ever. Or transfer a large software package to your computer via a USB drive. Do you get errors? Hardly ever. So why do you think you need such a special USB cable for music? I agree that if SPDIF interface is used, the receiving DAC can introduce distortion if the jitter is high, so there the cable has to be of high quality (as well as the source equipment) to minimize that. However when it comes to asynchronous USB, there is no jitter induced from the interface (no PLL is needed) and hence the quality of the cable is not critical as long as it's well shielded to prevent noise. I've tried many USB cables in my system, expensive and cheap, and could never detect differences. (I had golden eared audiophiles agreed). So if you think you detect differences in your system, it is likely a psychological effect IMO. Needless to say, the cable industry will not agree.