"That amazes me also. I always thought that changes below 1 dB in either of audio extreme is hard to distinguish, but when I make changes to EQ in those areas that are less than 1 dB, I do notice a change when A/B it "

You reminded me of something I had forgotten a long time ago. When I was in the sixth grade, they came around from the Junior High School to give a test to see if anyone who wanted to be in "orchestra class" the next year was qualified. What was the test? They didn't care if you ever heard of Beethoven or Mozart. They never asked. All they did was to play a succession of pairs of musical tones. You had to be able to tell which one was the higher pitch. These tones were so close in pitch, they probably weren't off by much more than an eighth note. It's not something I actually hear the way I'd hear adjacent whole tones, it's something I kind of feel like one tone is sour or the other is brilliant when comparing them. You can try this on a violin by bowing a string while rocking your finger slowly back and forth on the same string on the fingerboard. It's like very slight pitch bending on an electronic keyboard. If you concintrate, you may be able to hear more than you think you can. The rule of thumb that 1 db change in loudness is the limit of what you can hear may be a generalization of the population as a whole which doesn't apply to everybody. When one part of the spectrum changes relative to another by 1 db or even less, that change to the spectral balance may be audible. It's a change to the overall impression you get and it's sometimes hard to put your finger on. Now who really has the sharp ears and who just wishes or thinks they do?