RCA or XLR Between Digital Separates?

While in general I would expect an AES/EBU interface to provide superior performance, for the reasons that have been stated (and also due to reduced susceptibility to jitter that may be induced by ground loop effects), the following are some factors that might tip the balance the other way in some cases:

1)The AES/EBU signal may have faster risetimes and falltimes, which could worsen waveform distortion caused by signal reflections resulting from imperfect impedance matches, thereby causing increased jitter.

2)The cable and connectors used for S/PDIF may have more accurately controlled impedances than those used for AES/EBU, especially if BNC connectors are used for S/PDIF. I would expect a coaxial cable (used for S/PDIF) to provide more accurate impedance control than a twisted pair shielded cable (which is commonly used for AES/EBU).

3)Keep in mind that by changing from one cable type to the other a lot more than just the cable is being changed. The interface circuits in both of the components that are being connected are being changed, and there is no telling how the quality of the two interface circuits may compare.

4)While going to AES/EBU may reduce noise-induced jitter that would occur with S/PDIF (as opposed to jitter that may result from waveform distortion caused by impedance mismatches), depending on its spectral content a reduction in jitter could conceivably result in subjectively worse sound. As stated in this paper by Steve Nugent:

Another interesting thing about audibility of jitter is it's ability to mask other sibilance in a system. Sometimes, when the jitter is reduced in a system, other component sibilance is now obvious and even more objectionable than the original jitter was. Removing the jitter is the right thing to do however, and then replace the objectionable component. The end result will be much more enjoyable.

Jitter can even be euphonic in nature if it has the right frequency content. Some audiophiles like the effect of even-order harmonics in tubes, and like tubes, jitter distortion can in some systems "smooth" vocals. Again, the right thing to do is reduce the jitter and replace the objectionable components. It is fairly easy to become convinced that reducing jitter is not necessarily a positive step, however this is definitely going down the garden path and will ultimately limit your achievement of audio nirvana.

Regards,
-- Al

THANKS!
My post meant to generalize theoretically utilizing balanced or RCA connection between digital separates regardless of brand/wire quality and get the idea of advantages/disadvantages using one to another specifically in digital domain. My analogue in/out domain is fully balanced except phonostage and that's where I would less likely switch to unbalanced RCA even for the short wire runs.

Jitter is one of the issues I want to minimize since especially on the higher frequencies I can hear things different from real sound such as hissing, whistling and sometimes inconsistency especially if compared to the vinyl version of the music.

From this discussion I realized that technically the difference between both connections should not be subtle.

Thanks for all your contributions.

Mark M.

Al, you never cease to amaze me. I enjoyed your post. Interesting points, but balanced cables are still my preferred dance partners. :-)

Al,
I too enjoy your erudite and illuminating posts. Thanks!

I have used many high quality AT&T Glass, XLR and BNC cables between various transports and DACs and have found there is no way to predict which will work best with any given combination.

As an example; I recently replaced an expensive and highly regarded XLR cable, which worked great in other systems I've owned, with a relatively inexpensive BNC cable. The BNC cable bested the XLR cable in every respect in this particular application.

So unfortunately, as much as it would make life a bit simpler, there's no theoretical way to select the "best" digital cable. I'm always surprised by how different digital cables can "sound". I remember the old "bits is bits" days fondly.

Thanks very much, guys. Enjoy!

Best regards,
-- Al