Sorry to veer off-topic, but this always hits a nerve. The best, and likely the only scientifically valid, way to know if you're really hearing a difference or not:
Blind/ABX testing
Any claims of being able to discern differences in sound should be ignored unless valid, statistically significant, testing has been conducted. People who don't even attempt reasonable testing are, at best, fooling themselves.
FFT, THD, etc. measurements, while critical for design and evaluation, can't prove people are able to actually hear a difference.
It's incredible how many "audiophile" sound quality discernment discussions conveniently fail to even mention blind testing.
Of course even if folks demonstrate they hear a difference, via reasonable testing protocols, it's purely subjective whether it sounds "better" to them, or not. At least if they can consistently pick out one output over the other 90% of the time, they can legitimately say they hear a difference.
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"Doug Schneider, editor of the online Soundstage network, refuted this position with two editorials in 2009.[7][8] He stated: "Blind tests are at the core of the decades' worth of research into loudspeaker design done at Canada's National Research Council (NRC). The NRC researchers knew that for their result to be credible within the scientific community and to have the most meaningful results, they had to eliminate bias, and blind testing was the only way to do so." Many Canadian companies such as Axiom, Energy, Mirage, Paradigm, PSB and Revel use blind testing extensively in designing their loudspeakers. Audio professional Dr. Sean Olive of Harman International shares this view.[9]"
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(
https://en.wikipedia.org/wiki/High_fidelity#Listening_tests)