[opus] Why does opus scale down frequency from 22k to 20k ?

[Orange Ubuntero]

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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