Why do digital coax cables matter?

Digital cables are fundamentally different than analog cables.....the cable is an electrical transmission line at 44+ kHz. The 75 ohm impedance match at each end is critical for jitter, minimizing reflections, etc. BNC connectors are made for this, but Canare makes one of the only 75 ohm RCA connectors available......I've tried 'em and they sound better. Any good video cable in between works well, but the cable pedigree is much less important than with analog cables.

They do matter just listern to your ears + trust them,
I have tested many many digital coax cables + i found the more money i spent the better they sounded to me. this INMO
Opinan is down to the design,materials + connectors been,
used. the best digi coax cable i've ever tested + still own,
it the audioquest "eagle eye" at £700GBP per mtr!, it is just the business, solided silver conductor mutli sheilding,
+ DBS battery pack, its not hog-wash it works period!!!.

Almarg wrote:
"Do you feel that the following may also be significant contributors to sonic differences between S/PDIF interconnects, at least in some systems?

6)Differences in noise-induced jitter, due to ground loop effects and/or RFI/EMI pickup, both of which may be sensitive to cable differences.

7)Differences in radiated RFI, that may affect circuitry in the system that is not directly related to the S/PDIF interface."

These are both potential contributors to jitter, although #6 is not directly related to cable quality, and # 7 is mostly a function of the receiving device IMO.

As for cable pricing, I have found that in general cables below the $500 mark for 1.5m length sound about the same. Significant improvements are not realized until one spends more than $500. This is when you start to get the more exotic constructions, conductors and dielectrics, as well as better shielding. Just my experience.

Steve N.
Empirical Audio

Mapman wrote:
"on the several occasions where I have compared different digital cables going into my DAC(s), if there was a difference, it was not enough for me to take clear notice or even care. I know that in theory different levels of jitter is the result and that jitter level matters. But does it really in practice?"

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.

Steve N.

"Characteristic impedance different than 75 ohm can be very good, as Al mentioned, if it is better match for given system."

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.

"Same for slowing down the edges. Uncertainty of threshold is not caused by long transitions but by the noise."

Noise will certainly cause jitter (signal integrity or ground-bounce), but slow edges by themselves will also cause jitter and usually worse based on my experience. The problem is the voltage reference which sets the switching threshold at the receiver. This reference is usually noisy due to the system voltages and ground-bounce. Very difficult to make it noise free.

"With very little noise present longer edges might reduce impedance mismatch caused reflections, reducing jitter in effect. "

It sounds like common sense, but it doesnt work in practice. Faster edges and precise matching works a LOT better.

"Making cable "at least certain length" is not precise since cable is not even considered transmission line when propagation time (one way) is shorter than 1/8 of transition time being about 0.6m for typical 25ns transitions (assuming 5ns/m)"

I know this "rule of thumb", but really low jitter systems have risetimes of 3ns or less, not 25nsec. Even at 25nsec, the cable length helps however. the A/BX testing proves it.

Steve N.
Empirical Audio