The Importance of the Digital Cable

Thanks for the responses all. Calvin&Hobbes, Thanks for the great links and superbly detailed reply. 
So EMI / RFI comes to the fore again. Just as with streaming, this is a key culprit in sonic degradation.

Thanks GHDprentice, thats a great story on the transport to DAC. its exciting when one discovers how something considered less significant ends up making a profound difference. By the way, if you can remember what brand/kind of cable was it?

Of the two cables I mentioned, the Canare looks to be the better shielded of the two. The Veloce is beautifully constructed and ‘soft’ the way Chris does things (wonderfully), but the Canare is very well constructed too, with significant outer shielding and heavy duty connectors - although I prefer the Black Cat connectors and the general ‘feel’ of the cable. So If outer shielding has been addressed so well on the Canare, then it must be internal? I believe the metal / wire itself must influence the signal transfer integrity.

Hi Yuviarora, the Veloce I believe might use cotton as Chris utilizes Japanese cotton in his cables. You seemed to have delved pretty deeply here, trying different topology types.

Hello Melm, I thought the forum was open to discuss the subject we love. I have ‘googled’ but there is no substitute for talking with the audiophiles here with many years of practical experience. So are you saying that the digital stream/signal from computer to DAC is not a binary signal with packets etc., but rather a square wave, which is then converted to analogue by the DAC?

Jond, thanks, i will check out the Jorma digital cable.

thanks Roxy and Pauly for the response too

Yes, cable delivers digital information to D/A converter to produce analog (audio) signal. When this information is delivered in exactly same intervals then everything is always the same - perfect reproduction, but the problem is, that exact moment of D/A conversion can be affected by many factors and intervals become uneven (jittery). When this happens extra information is added to original signal. To understand this let’s imagine that you transfer constant 1kHz sinewave, but because of 60Hz noise moment of conversion (D/A clock) moves slightly back and forth in time 60 times a second. Now instead of pure 1kHz sinewave you will hear additional signals (sidebands) at 940Hz and 1060Hz at very small level. There will be many more, spaced by 60Hz, but because of smaller amplitude only first two (940Hz, 1060Hz) count. Amplitude of these sidebands will be proportional to amount of shifting in time (jitter).
These sidebands are extremely small, but still audible because they are not harmonically related to root (in this case 1kHz) signal. With many frequencies (music) there will be a lot of sidebands - practically added noise. This noise is proportional to signal level and without signal you cannot even hear it, but it is responsible for loss of transparency, loss of imaging, harshness etc.

So, now we know what happens, but why it happens? What can affect D/A conversion clock. To start with, this clock itself doesn’t have perfectly square edges and any noise in the system may add to edge (make it jagged) changing slightly moment of threshold crossing. What else? D/A clock has to be synchronized somehow with incoming S/Pdif signal, otherwise samples might get lost. It is done by taking average of S/Pdif signal word rate and using it to clock D/A converter. In spite of using average (no filter is perfect) timing variation in S/Pdif affect D/A clock. Where they come from? Electrical noise is obvious culprit. It adds to edges (making it jugged) changing moment of level recognition (threshold). Shielding, grounding, isolating etc. might help. It might be even worse for Toslink that being not sensitive to noise pickup is affected by system noise at both ends (Toslink transitions are slower).
Another culprit is reflection in the cable that adds to the edge (makes it jagged). This reflection happens when cable’s characteristic impedance is not matched to DAC input or Transport output. Beginning of the transition starts reflection from impedance boundary (usually cable’s end), that comes back and adds to rest of transition modifying its shape.

Characteristic impedance is very difficult to measure, so it is trial and error and expensive coax is not necessarily best match to impedances in your system. Shielding, of course is very important.

Hope it helps.

Hi Kijanki,

Thanks for that really superb answer. Very informative indeed. So you are reinforcing the notion that electrical noise i.e. EMI / RFI are the primary contributors to that very slight but audible change In sinewave i/ conversion clocked signal? So, aside from the clock itself, which as you indicate is never perfect, the cable transferring the digital signal is differentiated in performance primarily by ability to shield from EMI / RFI?

Hi MillerCarbon,

Thanks much for the input. I do believe powercords will be a positive upgrade for me, but I have yet to venture down that road though will in the near future. I am in the same boat as you regarding some of Synergistic Research’s products ( I have the Foundation speaker cables and set of four cable risers - which dramatically change the sound). As you’ve probably experimented with different types, can you state your preference for powercords and cables that are not priced into the stratosphere (I know some of your system is very expensive).

Yes, electrical noise will be very important contributor affecting not only transmission (creating time jitter), but also polluting everything else. Reflection created jitter in cable plays separate role. Reflections will produce time jitter of the signal hence added noise on analog out.  Two cables that have exactly same shielding may sound quite different because of impedance mismatch (one is a better match to DAC's input impedance).

+1 @kijanki  for mentioning timing, the influence of reflections in the cable and
how distortion affects the shape of the square wave. It's rarely mentioned how important it is to retain the integrity of the square wave from source to destination (DAC).