I think that double blind testing is essential. I have actually fooled myself. Upon receiving something new in the mail, I immediately hook it up, and am "astounded" by how much better it sounds that what it replaced. After a prolonged listen, and especially if I have my wife switch the component in and out, which is not double blind, but single blind, I find myself hitting it about 50/50, which means that I can't tell the difference. When we purchase some expensive tweak we badly want not to have lost our money that we justify it by things like, "less listener fatigue" or once long term break in has taken place it will fall into place. I've seen cables described as "a night and day difference" Well, while you're at work have someone switch one of them with out telling you which one, or even if nothing has been done. If it's night and day you'll spot it immediately.
Why is Double Blind Testing Controversial?
I noticed that the concept of "double blind testing" of cables is a controversial topic. Why? A/B switching seems like the only definitive way of determining how one cable compares to another, or any other component such as speakers, for example. While A/B testing (and particularly double blind testing, where you don't know which cable is A or B) does not show the long term listenability of a cable or other component, it does show the specific and immediate differences between the two. It shows the differences, if at all, how slight they are, how important, etc. It seems obvious that without knowing which cable you are listening to, you eliminate bias and preconceived notions as well. So, why is this a controversial notion?