Why do digital coax cables matter?

Sure, but I would sell that system and get one that meets the specs so I dont have to try to find a wacked-out cable that matches it.

How user can possibly know that wire or system meets the spects? I prefer to choose cable for the system and not the system for the cable.

This reference is usually noisy due to the system voltages and ground-bounce. Very difficult to make it noise free.

Yes, that's part of the noise I'm talking about. There is no perfectly quiet system and there is no perfectly impedance matched cable. It is always compromise. In noisy system (external or internal noise) it is better to get fast switching transport getting more of reflections but in very quiet system it might be better to get slower switching transport to minimize reflections.

Even at 25nsec, the cable length helps however. the A/BX testing proves it.

Are you saying that, assuming some impedance mismatch, 1.5m cable will be always better than 6" cable (that I used not long ago)? It doesn't make sens. There will be no reflections in 6" mismatched cable, assuming average transport (with 25ns transitions), but a lot of reflections in 1.5m cable. Even if the first reflection misses originating edge there will be consecutive reflections. There are techniques to predict effect of multiple reflections on the signal (Bergeron Diagrams) but it is very complicated task.

As for the measuring the jitter - effects can be measured but I agree with Al that it will be useless since it will depend on all the factors he mentioned. Measuring jitter effects at particular frequency in particular system in particular home etc. has no value to anybody.

Rower wrote:
"For digital, you just have to pass the eye-pattern level for proper digital signal retention. The more open the "eye" the fewer error bits, the lower the jitter. This should be the full channel, too. Cable and connectors both. You don't need expensive cables to virtually remove bit errors."

True, but we are not talking about bit errors here, we are talking about psecs of jitter. The cable matters, as does practically everything else.

Steve N.
Empirical Audio

"How user can possibly know that wire or system meets the specs?"

You can't. The best option for consumers is to read the reviews from a reputable reviewer and then try one.

"In noisy system (external or internal noise) it is better to get fast switching transport getting more of reflections but in very quiet system it might be better to get slower switching transport to minimize reflections."

Have you tried it? It sounds nice in theory, but usually does not work well.

"Are you saying that, assuming some impedance mismatch, 1.5m cable will be always better than 6" cable (that I used not long ago)?"

No, 6" cables are generally not commercially available. I'm saying that a 0.5m or 1m cable will not be as good as a 1.5m cable. In order to actually get 6" total, you would need probably a 3" cable since there is cable in the transmitting and receiving device.

Jitter measurements are a rat-hole IMO. Jitter has never been effectively correlated with SQ anyway, and based on my experience, it is very dependent on the spectral signature of the jitter. Single jitter measurements are useless to say the least.

Steve N.
Empirical Audio

Surprised nobody has mentioned the SPDIF clock which is an analog RF waveform (if I'm not mistaken) that must stay in sync with the data.

Not sure if AES/EBU any better in that regard, but it is supposed to be easier to guarantee impedance match (110 ohm in this case).

Some manufacturers like Sonic Frontiers implemented an I2Se interface to avoid these issues.

I guess my message is, if you supposedly need a $500+ coax cable to get the job done then maybe you need to choose a better interface. Stack the deck in your favor at least, don't be a victim!

"Perhaps you didn't test the right cables, or your preamp creates enough distortion, noise and compression that you dont hear the benefits because they are masked. This is fairly common when using an active preamp. I dont use a preamp, so I dont experience this masking anymore. It's a system after all, so every component and cable matters."

Maybe. But I do hear differences in most everything else I tweak beside digital source and ICs. So I think I have the relative magnitude right at a minimum. I hear a lot of systems and live music and I do not hear any distortion or dynamics issues of significance, but of course we know such things are always in play to some extent in home audio.