[PD] plotting freq response of [cpole~] (or "vcf")

[Alexandre Torres Porres]

the tricky math thingy is that is, well, complex...

worth noting is that the signal input is meant to be real, not complex, and
that this still creates two outputs (real and imaginary), in other words, I
needed to generate two frequency responses (one for the real and the other
for the imaginary part).

I just have no idea how to get there just by knowing [cpole~]'s transfer
function is H(Z) = 1/(1 - aZ^-1)

cheers


2014-08-05 15:59 GMT-03:00 Alexandre Torres Porres <porres at gmail.com>:

> Hi there, I have a patch based on mmb's work [filterplot.mmb]. It plots
> frequency response from biquad coefficients. I have it attached, as a
> default, it is plotting the freq response of a bandpass filter.
>
> So, I've been meaning to get the freq response of [vcf~] for a while now
> and I have the intuition that this patch may be adapted for that. [By the
> way, [vcf~] is basically a [cpole~] filter with the right coefficients and
> gain adjustment.
>
> The heart of this freq response patch is the subpatch that deals with the
> Z-Transform (that's what I believe anyway). In this case, it originally
> deals with the Z-transform of the biquad filter, but I believe that if we
> change it to cpole's tranfer function it'll work to plot vcf's frequency
> response.
>
> Right? Did I nail it?
>
> Well, if so... I've recently succeeded in getting the vcf's coefficients
> and gain to use them with [cpole~]. If you want you can check my patch
> attached. I'm generating the cpole's coeficients and everything, but the
> plotting subpatch still needs biquad coeficients to work. All that'd be
> missing is adapting the formula for the transfer function to cpole's.
>
> cpole's help file says that its Transfer Function is: H(Z) = 1/(1 -
> aZ^-1)... so it doesn't seem even hard to do it so. Unfortunately I'm just
> a geeky musician with no math background and needed help getting down to
> it. I tried some stuff in the dark and failed.
>
> thanks
> Alex
>
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