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In Reply to: RE: I don't think you understand the concept as much as you think you do posted by Dave_K on July 10, 2017 at 06:50:40
You've highlighted some valid qualifiers of the Sanders test in question. (I noted those as well three years ago when this was mentioned by "E-Stat" on the other forum.)
Yes indeed there are some issues with the A/B testing as Sanders as outlined it, but what I was trying to do then (as now) is give Roger the benefit of the doubt regarding his thinking on the basic validity of the concept. I'm not the originator of this, but I do understand what Roger is getting at.
I was then elaborating on his scheme with things that would make it much more valid. But by this time, the heels were well dug in by other posters. :)
The speaker crossover analogy was not the best, but I was trying to highlight a similar scheme that might be more understandable for E-Stat. He had suggested awhile back that for any common source split path network configuration all the characteristics would lump and yield identical signals at both destinations. (This is the basic premise of his whole rejection of the Sanders scheme.)
In the speaker analogy, yes indeed, even at the one frequency where the low-pass and high-pass filters are exactly the same amplitude there 'may' be a phase difference. But the "they do see the same signal" statement posited by Bob Rex is clearly incorrect.
I will stipulate this whole concept is tricky for some to get their heads wrapped around. Circuit analysis here and how some parameters lump is more complicated than it might seem.
The rest of your post regarding ABX testing clouds the issue, a bit. Typical audio sources not being theoretical voltage sources...non-used open-circuited interconnects...switchbox concerns, etc, etc, are all qualifiers that may invalidate the scheme. All of these (and others) I already noted three years ago.
Let me reiterate again....I have NEVER said there aren't some possible issues with the Sanders interconnect testing scheme. :) But unlike others, I don't completely reject it out of hand because of a few issues.
If you haven't already, check out the original paper from Roger Sanders and you decide how misguided his thinking is on this topic.
Thank you for the reasonable response.
My point of view on this topic is that when it comes to ABX'ing audio cables, the only way to make sure you're not introducing other variables into the audio system is to swap the cables, which is tedious and makes it impossible for the listener to utilize short term auditory memory to make the comparison. I can't think of any easy way to allow quick switching without introducing something into the circuit whose effect on the circuit performance is on the order of the cables themselves, if not greater.
Some time ago, I recall reading the comments of Frank van Alstine who insisted his second generation ABX comparator was completely transparent and suitable for cable comparisons because it had no active components or capacitors in the signal path, just a network of relays for switching and attenuators for volume control (he had gotten rid of the cap coupling in the second gen). The box contained a power supply, and digital control and display circuitry, and his single ended circuitry introduced a whole new ground path. It was essentially a digitally controlled passive pre-amp.
The underlying basis of the hypothesis is that differences in the relatively small impedances of audio cables and connectors, possibly combined with differences in shielding, or other construction details, is enough to make them audibly different to certain individuals in certain systems. Regardless of whether or not you believe this hypothesis to be true or false, in order to test it you have to preserve the details under which the hypothesis could be true. That is something that Frank and many other ABX proponents seem to have a mental block about.
In the case of Sanders, it could be that he just didn't think through the details of his proposal. Or it could be that he assumed a-priori that the cable capacitance couldn't matter, and therefore he didn't have to control for it.
Good points. Obviously you are correct that to 100%, absolutely, fully, maximize, etc, etc, control an A/B test like this, you would not parallel the interconnects onto a single source....without some facility to completely switch out the unused one.
I have talked with Roger a few times, but not regarding this interconnect cable test scheme. So, I'm not really sure what his specific thinking was/is.
Regards lumping of characteristics: If we really want to get down into the weeds on this, the capacitances of two, simultaneously connected interconnect cables do not strictly appear in parallel with each other. Even a simplified equivalent circuit would illustrate this. There are multiple series and shunting elements to consider.
Regards possible ABX testing and gadgets to achieve it, it really is a can of worms with numerous potential pitfalls. I'm well aware. :)
> I have NEVER said there aren't some possible issues with the Sanders interconnect testing scheme. :) But unlike others, I don't completely reject it out of hand because of a few issues.>
Not possible issues - ISSUES.
You don't reject it, even though it is flawed, because it fits your biases.
So if you don't control ALL of the variables in a scientific test, how is it a valid scientific test?
Do you understand the scientific method?
Your test is pseudoscience - a parlor trick to make audible differences disappear.
So it's MY test now?? :)
I'm not the one that came up with this scheme.....let's not lose sight of that.
AND you've identified by biases too. Excellent! :)
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