One reason why most people can't hear the degradation may be that the "high frequencies" they hear are closer to 7kHz than 20kHz.
Yes, I partly agree with you.
I am sorry getting a little bit out of the scope of this thread and our present LP cleaning issue, but...
Very fortunately, I have considerably better hearing ability over the average ability of my age group; I periodically check my hearing ability using a free software audiometer with nice headphone. I well know and understand, however, my hearing ability in 7 kHz to 20 kHz (or
ca.15 kHz?) is now a little bit inferior to average of younger people; by younger people, I mean people of age 40 or less.
Consequently, in case I invite those younger people to my audio listening sessions, they highly possibly feel that my best tuned high Fq response over 7 kHz (for my ears and brain) would be a little bit too high-gain for their ears. This means it should be better that if I could have flexible Fq response adjustments in my audio system especially in 7 kHz to 20 kHz Fq zone.
I have been intensively implementing flexible gain tuning functionalities which can be done "on-the-fly" (while listening to the music), very safely, flexibly, and smoothly (not step-wisely). From safety point of view, it is critical that such flexible relative gain tuning can be applied even while all of the DSP(XO/EQ/delay) "EKIO" parameters in upstream PC as well as preamp gains of DAC8PRO remain unchanged (they should stay "untouchable"). And, this is one of the major reasons I decided to use HiFi-grade "integrated amplifiers" in my multichannel multi-amplifier audio setup.
For further details, you would please refer to
my specific post here on my project thread.