[earlevel]

Originally Posted by Nowhk

Well, in fact what I'm doing is a VST FX with 3-Band EQ. Thus, I'm using 3 RBJ's Peak filter in series.

Since I'm a newbie of these stuff, I've started using that basic One Pole filter above (which should be an EMA filter) to easily study, apply, catch FFT and plot the frequency response graph.
The things later has been evolved, so I've added another order to it (i.e. two EMA in series) and add that Resonance stuff (which, if I well understand from your words, that filter become a SVF filter, wrote by Martin).

That's all: I just asked to you how to place the coefficients of this "hybrid" SVF filter inside your "evaluating the filter frequency response" code/article to catch the exact response, but I think that's not possible with that filter. Was like a sort of "homework" task, to learning more Anyway, evaluating the filter frequency response of that SVF doesn't matter anymore if I'll use RBJ.

You're were putting two one-pole filters in series with feedback? No, that's not the same as a state variable filter. And even if you used a state variable filter (two coefficients), you couldn't use the same coefficients as those calculated for a direct form biquad (five coefficients).

Since it will be an FX/EQ, RBJ filters should be good for my purpose right?

When you say you're using three rbj peak filters in series, I guess you mean that you're now using three direct form biquads? (I recommend direct form II transposed, if you want direct form with floating point calculations.) Along with rbj's calculations for the coefficients? Yes, that is suitable for the task.

What do you mean with "just different derivation"? Doesn't only matter the coefficients at the end? If they are equal, why I should use one or the other?

I mean exactly that—I have biquad coefficient calculations, rbj has different calculations. They only differ in the derivation—they produce the same numbers.