Does Digital Audio capture everything?

[KeithL]

The first part of the answer is that not everyone agrees that "nobody can hear it under any circumstances".
All of those tests, which everybody repeats, over and over again, are based on steady state sine wave tones ("press the button if you hear a tone").

However, human hearing, and especially the human brain, can be very complex.
For example, very few of us could hear a 22 kHz sine wave.
However, does that mean that we couldn't hear the difference between an 11 kHz pure tone, and one with some 22 kHz (the second harmonic) mixed in?
To be blunt, it sort of suggests that might be the case, but it doesn't prove it.
The world is full of situations where, thanks to the incredible complexity of our human senses, we sometimes get surprising results.

For example, what if we were to find that, if we played that 11 kHz tone, with and without the 22 kHz harmonics removed, everyone agreed that it sounded exactly the same.....
Except that, with the harmonics included, it sounded like it was coming from four inches further to the left?
(This isn't as far-fetched as it sounds, since our brains use all sorts of cues, both consciously audible and subliminal, to locate the sources of various sounds in space.)

Please not that I am NOT specifically claiming to have seen positive proof that the presence of frequency content above 20 kHz can make an audible difference.
However, again to be perfectly blunt, most of the tests claiming to show the opposite have been rather poorly designed.
And at least a few tests have produced results that seem to show that at least some people CAN hear the difference.
And, from listening to lots of different DACs, on lots of different speakers and headphones, I can tell you that certain subtle things really are also only noticeable on certain combinations of equipment.
(So the fact that they weren't audible in a specific test, using specific equipment, and specific samples, doesn't necessarily prove much.)
I would suggest that, at a very minimum, there are enough test results showing that some people can hear the difference that "it still needs some more study".

You may have heard that humans can't see "infrared light" (that's why we call it INFRA-red)...
And that we certainly can't see the color emitted by most common IR remote controls...
However, that isn't actually true....
Our eyes are quite insensitive to light at around 720 nm - which is the color common to most IR remote controls...
Therefore, you tend to not notice it, or even to be able to see it at all, at the brightness of most remote controls...
However, if you find yourself a 720 nm LASER, you'll find that you CAN see it - if it's bright enough...

Apr 12, 2018 10:17:58 GMT -5 pedrocols said:

I always wonder what is the benefit in real word listening to a FR above 20/20. How is it better if NOBODY can hear it?

[geeqner]

I KNOW that at least, at lower frequencies, human ears can pick-up differences between pure Sine Waves, Square Waves, and Sawtooth (Ramped) waves of the same frequency. The sounds produced can take-on different audible / perceived "characteristics", (Some Synthesizers have the capability to create the different wave types.)

I do not know if this still holds water at higher frequencies and/or what the upper-limit of being able to tell the difference is

A LITTLE MORE "ENGINEER-ESE" FOR YOUR CONSIDERATION:
However, I DO know that (at least, OUTSIDE of the Audio Realm) - the difference between the different Wave Shapes of the same fundamental frequency CAN be related to the ability of the system to handle Higher and Lower frequencies. Most complex, repetitive wave forms can be synthesized by ADDING together Sine Waves of several different frequencies and amplitudes, such that they add-to and cancel-out portions of eachother in a way that creates a close approximation of the desired Wave Shape.

Working in the other direction - a tool called "Fourier Analysis" can break-down a particular defined wave shape into the main fundamental frequencies that could be used to generate it.

Creating an ACCURATE 20 kHz square-wave would require SEVERAL component Sine Waves to be added - many of them at SIGNIFICANTLY higher frequencies than the 20 kHz fundamental, in order to produce a reasonable approximation (to "fill-in" the square corners of the wave form). I believe that THIS is where the "nuance" in Hi-Fi Systems that are capable of handling super-Audio (and Sub-Audio) frequencies comes into the picture.

[Plus the ability to FAVORABLY exploit the trade-off between

• Actual SIGNAL at such frequencies (if such Signal Content actually EXISTS within the Source Material).
• The ability to filter-out / minimize any NOISE at such frequencies]

With a system consisting of suitably high-end components and speakers, within a room with excellent acoustical properties, one may be able to PERCEIVE the differences offered by such systems more so than actually "hearing" them. (But above and beyond some point and the acoustical acuity of the given listener - it becomes "hogwash")

[Casey Leedom]

A Square Wave comprises all the odd harmonics of the fundamental ...

Casey