I've participated in a number of double blind tests over the years regarding this vary sort of thing, where caps, tubes, wire, you name it was subjected to this kind of testing. It was a non-scientific (I'm sure some element of strict protocol was violated), scientific (a strong effort was made to make it an honest a double blind scenario) study a couple of decades ago conducted among friends and fellow enthusiasts. Probably close to a dozen tests in all. In a nut shell, virtually all the claims made for improved sound from certain caps, tubes, and wires etc. basically went down in flames, with never a majority of contestants that could accurately state when a change was made, and to which component of those being tested over 50% of the time. The power of expectation bias is huge when you are intimately involved with making the changes (therefore knowing when it was made) and making the audible determinations that result from those changes -- this on top of dealing with subjective judgements being hard enough to begin with. The problem is, those in the camp that feel that different caps do sound different believe what they believe (they're entitled to), with no amount of scientific testing results being able to prove otherwise in their minds. It always falls back on the test procedure somehow being defective, and you don't hear what they hear. Fair enough, so the best you can do is respect each other's position, and agree to disagree.
Because it is such a passionate subject, I don't really chose to engage such discussions much anymore, other than to report what the tests I was involved in revealed, to the virtual agreement of all involved. For me, quality parts will get you there 99.9% of the time. But there are cases where components do make a measurable/audible change, such as sometimes when oversized caps that are many times the physical size of the original device are shoehorned into a place that was never intended to have such a large component installed, and then interacts with adjacent circuits in a way that the original components never did. But I realize -- and respect -- that not everyone agrees with this point of view. It is discussion that is a product of the new age of vacuum tube audio (it used to be we only argued about whether triodes or pentodes sounded better!), and likely won't get solved anytime soon. If it ever does, it will just be replaced with some new controversy! What would audio be without it?
Dave
Because it is such a passionate subject, I don't really chose to engage such discussions much anymore, other than to report what the tests I was involved in revealed, to the virtual agreement of all involved. For me, quality parts will get you there 99.9% of the time. But there are cases where components do make a measurable/audible change, such as sometimes when oversized caps that are many times the physical size of the original device are shoehorned into a place that was never intended to have such a large component installed, and then interacts with adjacent circuits in a way that the original components never did. But I realize -- and respect -- that not everyone agrees with this point of view. It is discussion that is a product of the new age of vacuum tube audio (it used to be we only argued about whether triodes or pentodes sounded better!), and likely won't get solved anytime soon. If it ever does, it will just be replaced with some new controversy! What would audio be without it?
Dave