Digital cable length- SPDIF vs AES/EBU- 1.5 meter for either?

Sorry, just saw this thread. Are you all saying any coax digital cable that is not 1.5m long should be tossed out? Why are they even manufacturing cables that are in different (from 1.5m) lengths?

Are you all saying any coax digital cable that is not 1.5m long should be tossed out?

Kalali, please read the posts by me and by Kijanki dated 1-25-2016. As you’ll see, there are numerous technical variables affecting what length will be optimal in a given application. Some of those variables are almost never specified (e.g., the risetimes and falltimes of the signal provided by the source), and some have little if any predictability (e.g., susceptibility of the two connected components to ground loop effects, which can contribute to jitter at the point of D/A conversion).

So as I said in concluding my post:

I would consider Steve’s recommendation of 1.5 meters to at the very least provide the best odds of being optimal.

This assumes, btw, that a very short length, such as say 6 inches, is not practicable. In circumstances where it is practicable, I suspect it is likely to be an even better choice than 1.5 meters.

Also, past threads here have provided anecdotal evidence that 1.5 meters is not always the best choice. Some members have reported making direct comparisons of 1.5 and 1 meter cables that are otherwise identical, and preferring the 1 meter length.

Regards,
-- Al

Also, some comments on the Lessloss writeup that Steakster linked to, which I disagree with to some extent:

It makes no mention of the effects of length on the **timing** with which signal reflections arrive at the destination component (i.e., the DAC), and instead focuses mainly on the amplitude with which those reflections arrive. But in a home system application what is **far** more likely to be significant (for a given set of component and cable impedance values, within their respective +/- tolerances) is arrival time, as explained in Steve Nugent’s paper that was linked to earlier in the thread. Not arrival amplitude, which won’t differ greatly as a function of cable length, in home system applications.

In fact the Lessloss paper itself states that it provides a "reflection-attenuation network, built into the very cable itself, ... [which reduces] the level of the first reflection by 5.6 dB. This is equivalent to a silver digital line of this type of 117 meters in length."

5.6 db is a reduction of only about a factor of 2, in terms of voltage, which by their statement would occur without the special built-in network only if the cable were 117 meters long!

The reason timing is what matters is that what the DAC detects are the **transitions** between the high voltage and low voltage states (and vice versa) of the signal it receives. If the reflections arrive at times in between those transitions, or at times during those transitions that are not close to their mid-point, they will be ignored.

That said, I have no specific knowledge of how the reflection-attenuation network of the Lessloss cables may be designed, and no experience with or knowledge of the sonics Lessloss digital cables may provide in typical applications. In any event, though, it sounds like the inclusion of the special network in their cables means that the rationale for the usual 1.5 meter recommendation is inapplicable in their case.

Regards,
-- Al

Al, thanks as always for the thorough explanation. I saw the references to the comparisons between 1.0m and 1.5m cable lengths but was left with the impression that longer lengths were not desirable, all things considered and being equal. To your point, I find it difficult to believe a single length could be optimal in all circumstances given all the other variables, including the cable material and construction techniques.