“human hearing in many ways is not extensively understood or measurable, and there certainly are individual differences...the process is the same, but the results are different...”
based on what? As I mentioned before I try to pay attention to actual scientists in the field of psychoacoustics and the actual studies. According to scientists such as James D Johnston and Floyd Toole among others we know a great deal in deep detail about what humans can actually hear and can’t hear and have a pretty detailed map of how that correlates to measured performance in audio gear. In so far as the electrical audio signal in particular is concerned it is very well known as to what makes an audible difference and what does not. It does get more complicated once it’s about sound waves in three dimensions. What scientific sources are you getting this conflicting opinion from that states human thresholds of hearing are not so well understood? Honest question. Even in the world of high end audio we do have some substantial differences of opinions among top scientists. But none that I know of regarding thresholds of audibility. So honestly, if you know of any conflicting opinions from the scientific community I’d very much like to know about it.

