First, thank you esldude for your kind reminder as to nature of this sub-forum. I am expecting this post to be the last one before a probably swan song.
Thank you Jinjuku for the engagement and the respect ... though, you and so many others seem to not actually have read what I've written about directionality. Maybe a case of expectation bias?
Most significant, I have never claimed that the signal is directional, whether analog or digital (actually, there is only analog, digital is the information conveyed through an analog medium, but as a history major, I'm not the one to be explaining this as well as the tale can be told). In the past I didn't even posit a mechanism for directionality, though I never believed that it was the signal which was directional.
Multiple decades ago, Charlie Hanson (the creator and designer of Ayre Acoustics and definitely one of the most brilliant minds and most capable engineers the audio world has benefited from) and I mused together about directionality. We both had noted that all conductors, positive and negative, needed to run in the same direction. We had both noted that while conductor direction was consistent between low level components, to the power amp, and on to the speaker, that if the same metal is used for an AC cable, the direction was instead of to-the-speaker, that the correct direction for an AC cable was to-the-wall.
We had both noticed that the sonic signature of a cable in the incorrect direction was similar to the sound of the type of active circuit misbehavior that's often the result of EMI. Charlie made reference to the benefit of a cable being used in the correct direction as being "akin to diode rectification." Charlie is very, very careful with his words -- he said "akin to", not "because of" (!), so please don't get distracted by why diode rectification in a conductor is impossible. Charlie is a polymath, and he's also a totally no-room-for-BS engineer -- but Charlie the scientist also enjoyed pondering the empirical evidence, not looking to disprove the empirical evidence. Something Charlie had observed only tickled him, because evidence of the frontier of knowledge tickles a scientist.
About the mechanics of testing for directionality, whether using ears or other devices, because if the experiment is done without sufficient respect for the possibility of an unexpected outcome, the experiment itself might well be fatally flawed, as is the case with two of the methodologies described:
Almost all single-ended audio interconnect cables are twisted-pair with a shield only connected on one end. Such a cable cannot be turned around for the purpose of investigating directionality without reterminating the shield, full stop -- and, as the shield dumps far more RF garbage on the end it's connected to than either end of the ground conductor, an unshielded cable, or simply the shield not terminated at either end, is required for any valid test of conductor directionality.
AudioQuest cable models which are available with XLR plugs, never conform to the diagram shown in Jinjuku's post. This is (I believe, I certainly tried) described very clearly in all written materials about AQ balanced cables, on the cable's box and on our website. The shield is never used as a conductor. All AQ cables with XLRs have 3 conductors plus a shield, which is only connected at one end. One would have to reterminate both ends, more than once because the first retermination would not be the equivalent of the cold-weld (or resistance-weld in the past) by which AQ terminates cables.
Because directionality is "all about noise" (as my ad headline says, which has even been posted on some cable-fight forums this week, though of course not read by everyone), connecting more than one cable (or stereo pair for analog) between chassis voids the experiment. This is about as good an example as the subjectivists could ever hope for of how tests "disproving" what they know are rigged, of course not always intentionally -- though they might justifiably suspect that working towards a desired outcome prevented truly trying to isolate all variables to the extent awareness and technology allow. "Proving" that signal is not directional is not a test of whether conductor directionality exists or not.
Whatever an expert can or cannot measure with test gear, or whatever a listener can or cannot hear, I think can be best facilitated by a single cable, usable for S/P-DIF or analog (only some not-power dependent USB gear will even work with such an out-of spec not-a-USB cable). I recommend testing be done using two uninsulated and unshielded solid conductors (so as not to be concerned that not all strands run the same direction, the two solid conductors having been cut from a single conductor so that their relative direction is known), with identical plugs attached in the same manner, on both ends. This one wire, when tested, needs to be turned one way, and turned the other. Our experience is that directionality, as determined by using bare conductors, always yields a similar benefit for USB, Ethernet, HDMI, S/P-DIF, AES/EBU, FireWire, AC cable and analog.
For optical, directionality can be observed, but at present I am of the impression that this is due to slight variation in the angle and polish and excess glue, etc. in the termination process -- though I do not know enough to completely rule out that fiber-optic manufacture might not introduce some asymmetry in the impurities which scatter light, contributing to a smearing of the same data across time. There is partial correlation between dB loss figures and resulting audio performance in single-fiber Toslink cables -- however, our best Toslink cables have far more loss because there is less surface area for a multi-fiber cable. The improvement in a higher-loss multi-fiber cable is very simple, and one of the few times that a visualization tells the whole story. The enemy is not amplitude, it is dispersion over time due to the incoherence of the light source (an LED, not a laser), and so the smaller aperture of each fiber in a multi-fiber cable benefits from the reduced size of the aperture in a manner similar to how a pin-hole camera doesn't need a lens.
Definitely a stretch as an analogy, and a subject which is unbelievably and sadly political, climate change. Well of course the climate is changing, it always has. One of those long term changes is in precipitation per year. The top of Kilimanjaro is always below freezing. None of the loss of snow and ice atop Kilimanjaro is due to warming, natural or accelerated by man -- the loss is due to sublimation taking away more of the snow than new precipitation restores. Does this reality, and that it makes those who use the declining snow on Kilimanjaro as a poster-child for man caused climate look like liars, mean that therefor climate change is a lie?
No, in most cases, the "perpetrator" doesn't know about sublimation, sort of like not knowing that noise, not signal is at the core of directionality. And, while the claim that the snows of Kilimanjaro are melting is false, like the D-Tronics video that's the point of this thread is false, that doesn't mean that climate change isn't real, or that cables differences don't exist.
To DaveC: Thank you for mentioning As-Cast metals, and that amorphous materials are a different species. In the more fleshed out version of my discussion of directionality, I specifically mention the difference between As-Cast and drawn metals.
To FratzM: I cannot comment on the charged-ground system used by Synergistics, which some people have confused with my dielectric-biasing system, but I can explain that the DC potential applied to many AudioQuest cables is only a DC potential, not a current, and that as such (a not-changing electrostatic field), there is no intermodulation with the metal conductor, or with the signal. The reduction in distortion is only due to better forming the cable's dielectric, reducing the time-smearing caused by the fact that from one perspective, a cable is just a long capacitor.
And in case this is my swan song for non-measured results on this sub-forum, I want to reply to those who have speculated that it was easy to sell analog cables, but difficult to sell digital cables -- because the truth is very much the opposite. My theory is that in the analog domain, the people who didn't want there to be difference, that once they heard a difference, they acted on or dismissed what they heard as being simply LCR (even when many of the different cables had identical LCR) -- but in the digital domain, when people are surprised by what they do hear, they are much less likely to have a fall back position. They seem more likely to resort to accusations of inadequate listening methodology (which is a real problem on all sides), or they take on a scientist's perspective -- not meaning that they go on a scientific quest, but that they act on the empirical evidence as available and appropriate for them. This has also fortunately meant that many manufacturers with expertise in other areas, who were always cautious about cable recommendations and the politics of brand distribution, have to an astonishing degree made a point of demonstrating their own gear with AQ cables, and sometimes strongly recommending that their dealers do the same. We never had it so comparatively easy before digital.
That some of the designers of some of the world's best audio products recommend the cheapest HDMI or Ethernet cable, or any speaker wire of sufficient AWG, etc., only shows that there is disagreement within the audio community. There always was, and there always will be. Diversity is one of the most fundamental strengths of civilization.
Thank you, Bill Low