Orfanidis prescribed nyquist peak filter parameters

>Back to this project after a long break.
>
>I've gotten decent behaviour however when the peak frequency approaches
>Nyquist the bandwidth expands like so...
>
>https://s13.postimg.io/pfj6t5tvb/orfanidis_near_nyquist_behaviour.gif
>
>Any ideas of how to iron this out?
>
>I've chosen 0.707*peak_gain to be the gain at which the bandwidth is
>measured at. I'm presuming something strange is happening when the
rightmost
>bandwidth frequency is hits and exceeds Nyquist?
>
>Many thanks,
>John.

That's how it works with 'low Q' value. 

I would try other method(s) for filters above fc where Orfandis' method
starts give wrong output response. 

Särkka/Huovilainen paper "Accurate Discretization of Analog Audio Filters
with Application to Parametric Equalizer Design" -
https://users.aalto.fi/~ssarkka/pub/eq-article.pdf might work if you tweak
the method a bit. If you like to test their method in Matlab/Octave you'll
find ready to use functions for that paper from
https://users.aalto.fi/~ssarkka/pub/ (eq_desifn_demo.zip)).

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>I've gotten decent behaviour however when the peak frequency approaches
>Nyquist the bandwidth expands like so...

You could try other matching schemes as outlined here:
http://vicanek.de/articles/BiquadFits.pdf
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