"Some highly trained listeners can hear a very slight difference when 20kHz band-limited audio signals are compared with wide band signals with certain test material. Under extraordinarily good listening conditions using exceptionally good systems of reproduction with extended response to 40 khz"
Sorry to mention it in this discussion, but the ground was laid anyway.
My system/speakers (2-way Dyns) is probably not made, nor capable extenting up to 40KHz, neither my personal HF hearing limit is higher than 15KHz (on one ear), but I guess up to 25-30KHz are reproducible by the system. The rest of the equipment is OK, from a distortion point of view.
Now there are 2 incidents which you might be able to reproduce by yourself, where I heard differences in the higher frequency range. Speaking in Critical Bands it were probably #22, #23 and #24, ranging from 7.7.-15.5KHz (all with rather broad bandwidths from 1.8-3.5KHz, so there is probably no accurate frequency identification possible).
1. Take e.g. the before mentioned live recorded Thin Lizzy concert from 1978 (Live & Dangerous), which is available as a 192KHz sampled files. It contains significant frequency components above 24KHz, probably directly recorded on 15ips tape, with some 30KHz limit (if I remember my retired Technics RS-1506 capabilites correctly)
Downsample that to 48KHz (not even 44.1) with e.g. SOX (I used the command line setup with max. quality and proper settings).
That did not sound as bright and precise in the mentioned range, as the original file. In contrast to the below, the 48K tracks exibited no increased distortion impression. Sampling down to 96KHz and comparing to 192KHz revealed no audible difference
2. Take some DSD or SACD-ISO, run it through that foobar converter plugin to 88KHz/WAV/FLAC (best quality) with or without 30KHz filter and there is as well a difference audible. Without filter, the sound is brighter, combined with some harshness, maybe described similar as if there would be 3rd order distortion (as we learned above, noise in magnitude of the audible signal itself). With the filter it sounds simply clean and not lacking some high frequncy components. That high frequency energy above the hearing band without filter is even visible in the file size, these files are some few % larger, than the filtered ones. Doing these tests at decent loudness, they shouldn´t have exceeded the linear range of my equipment.
In both cases listen to cymbals, there it became most audible to me.
I am not saying everybody is able hear it, maybe even younger listeners are not able, because their hearing system (from eardrum to "brain processing") does not exibit as much distortion as from someone in my age >55.
From other experiments running a frequency sweep on one channel and fixed frequencies of 1 - 3KHz on the other, revealed beating (difference) tones around identical frequencies and also weaker ones at multiples of the fixed.
In my case, maybe some estimated 20-40dB lower than the original ones.
These difference tones vanish of course, when listening by headphone, until you "mono" the signal, then as well audible. In that mono case no significant difference was audible, when listening by speakers.
Cutting a long story short, my five cents are that the human hearing system mixes down ultrasoninc content to the audible range in a "broadband or bulk manor" due to nonlinear effects.
Anyway, in the first example it sounds better to me, when not downsampled below 96KHz.
Give it a try yourself!
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