Le 2012-02-02 à 11:40:00, Mathieu Bouchard a écrit :
So a real ax²+bx+c is something between a pair of [rpole~] and a pair of [cpole~]. It's equivalent to a pair of [cpole~] in which you force two numbers to be the same, and two other numbers to be negatives of each other.
Actually, [bp~] is pretty much a 2-pole resonant real filter, right ? The input parameters f (centre freq) and s (sampling rate) and Q are transformed like this :
ω = 2πf/s r = 1-ω/Q a = -r² b = 2r*cos(ω)c = 1 (an overall gain is applied separately, which is like scaling a,b,c all at once)
however, in this case, b²-4ac = 4r²*(1+cos²(ω)) is always positive, so it does not cover the unfactorisable cases, which have to be done using [cpole~] or [biquad~] (whichever is more efficient). It seems that [bp~] is a mere combination of a [lop~], a [hip~] and a [*~] (plus the calculation of their coefficients).
I'm still learning about this topic... so, again, I might be saying something wrong in there.
______________________________________________________________________ | Mathieu BOUCHARD ----- téléphone : +1.514.383.3801 ----- Montréal, QC
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