Hi,
I'm working on the digital filters and I've read this paper "Improving the Chamberlin Digital State Variable Filter" ([2111.05592] Improving the Chamberlin Digital State Variable Filter). Digital State Variable Filter is explained in a more modern fashion and authors (Lazzarini et Timoney) propose to a very interesting improvement for high frequencies and add the Bandreject and the Allpass filters.
My first intention was to use the Csound biquad opcode with the parameters calculate from the transfer function. It works well except for the Allpass filter. There is no inversion of the phase at the cutoff frequency, phase is always at 0 ! I make a mistake certainly.
From an efficiency view, is it better to use the opcode proposed in the paper (opcode Svar3) based on the difference equations or using the biquad csound opcode ?
In a previous thread, I see that statevar opcode implement the state variable filter. Is it the old Chamberlin design ? Can we expect a new opcode based on the paper ?
Regards.
T. Aimé
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