opus - Aug 2012 - Why does opus scale down frequency from 22k to 20k ?

Why does opus scale down frequency from 22k to 20k ?
64kbps<https://lh5.googleusercontent.com/-DGsEd1ijTBs/UDE3OFVrE5I/AAAAAAAADBo/bFcWQ6I4-Zk/s588/opus_64_test.png>

128kbps<https://lh3.googleusercontent.com/-3Wfvq6OPGRw/UDE3OClxEdI/AAAAAAAADBk/vsBJ9Gcd_pU/s589/opus_test.png>

192kbps<https://lh4.googleusercontent.com/-tfDAtdGM2Aw/UDE3N3mrFJI/AAAAAAAADBg/38weacOnQ7I/s588/opus_192_test.png>

this action will affect the quality of audio.

*Can this feature be disable in future ?*

And

*Can opus add no noise and echo in audio at high kbps *(192kbps +) *?*
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Orange Ubuntero wrote:
> this action will affect the quality of audio.
Any affect will be inaudible to human ears. For a more detailed 
explanation, see http://people.xiph.org/~xiphmont/demo/neil-young.html
> *Can this feature be disable in future ?*
No. It is not possible to encode information for frequencies above 20 
kHz in the bitstream, even if an encoder wanted to.
> *Can opus add no noise and echo in audio at high kbps *(192kbps +) *?*
Opus is a lossy codec, so it will always change the numerical values in 
the actual signal. But if you can find a sample that you can distinguish 
from the original in an ABX _listening_ test (as opposed to by looking 
at a spectrogram) at 192 kbps, then we'd certainly be interested in 
knowing about it.