The question: “Does HD Audio matter, and why do we need to produce frequencies above 20k” still nettles me.
Today, while taking an exceptionally beautiful walk through the Bavarian forest near my house, I head some insights, that I’m about to share with you.
1.) A lot of research points out, that the human ear is incapable of hearing anything above 20k and hence reproduction, recording and transport of frequencies above that are unnecessary.
2.) David Blackmer pointed out here, that 2/3rds of the hairs in the human cochlea are used to detect not the frequency, but the waveform of incoming audio.
Blackmers rearch has apparently been refuted, or could not be reproduced. His findings still make a lot of sense to me, seen from biological or evolutional viewpoint. Now I am very well aware of the dangers of biologisms and other half-baked cross references, still, consider this:
Say, you are in the woods, looking for food, or an animal that you might hunt, at the same time, aware that you need to stay clear of wolves, bears or sabre-tooth tigers. Hearing is very relevant to that task. Specifically, the transients of the incoming audio make all the difference. A sharp, short spike, when an animal breaks a twig or steps down upon dry grass is very different from wind blowing through trees. This difference is in the micro-second time domain and is vital to your survival.
So to have a lot of capacity dedicated to distinguish waveforms, transients and rise time, makes clear sense.
Why can this not be detected in tests: I believe that these tests ask questions from a frequency domain point of view. Not from a time domain point of view.
And here comes the hard part: some argue that since frequency requires time, there is no need to look at the time domain. This seems correct, but on closer inspection puts the horse before the cart. Time is primary, frequency secondary. With time comes frequency, but frequency requires time!
So, yes, the human ear cannot hear frequencies above 20k. But also: waveform detection, rise times and transient response are of utmost importance to natural sounding reproduction. I could detect that time and again, without knowing about the rise times of the equipment being used.
I suggest that the human ear has different windows for the frequency and the time domain. Frequency is limited to approx. 20Hz to 20 kHz. Time is very sensitive to small differences in waveforms and transients.
I would be very interesting in any research about that, that does not stem from a frequency domain point-of-view and would love to collaborate to develop adequate tests. So if you are thinking about hearing, working in the field of hearing research or just want to team up, please do not hesitate to leave your comment below or contact me.