Originally Posted by mcnarus
And where did that .2 dB figure come from? I doubt a rolloff anywhere close to that magnitude at 20 Hz would be audible.
That's what the tests have shown to be audible. Remember, you're liveswitching between the before and after to try to hear a difference. And do note that below 20 the difference is also increasing and the studio rig used in most the tests have capabilities well below 20. If I remember correct, it's the frequency drop part of Eric Serra's "Mondoshawan" that's used to test that. Track 2 on the Fifth Element soundtrack.
After you've statistically proven a difference, you can certainly resort to measuring it - that's why you'd know.
This isn't some local gang we're talking about. It's a society that's existed since the 1950s and consisted of top radio-,tv-,recording industry people as well as electronics and speaker designers, music artists and both music lovers and audiophiles. They're using the best ears they can get hold of and the equipment and environment is top notch and well controlled. It's a studio used to educate studio people. I myself is not involved, so don't judge the people or the method from judging me. I'm just a regular member of the society to get their magazine and attend a local meeting or outing now and then.
AB(X) testing is about testing differences between two unit. That's completely uninteresting as there exists no reference. Before/After testing tests one unit against the reference - which is the input to it. If you test two units against each other and find them the same, then they are the same, but are both great or are both crap? With no reference in the test that can't be determined.
Now, you may very well argue that it's not the design goal of all amp to just amplify the signal, and of course - for those the before/after testing is irrelevant. It's a good way to determine what that designed change to the sound is, though.
It's quite intriguing that people claiming to cheer for science isn't interested to challenge their beliefs and give a new method presented a good think through... it is one of the fundamentals in science to continually question itself.
Anyway, the thread is for cables, not amps, so I'll stop here. If anyone is truly interested in knowing more, use the PM function.