Forums > MaxMSP

Q factor and resonance in resonant filter

Dec 05 2009 | 1:46 pm

I need to calculate from scratch the coefficients for a resonant filter, and I’m no DSP guru…

googling around, I found the following formulae – which work fine, indeed:
a1 = -2r cos(2πfT)
a2 = r*r
b0 = g*(1-a2)/2
b1 = 0
b2 = -b0
with f being the center frequency, g the gain, r the resonance and T = 1/sr
(actually, in the filtergraph~ doc the a’s and b’s are swapped, but most on-line resources name the coefficients like this)

anyway. I’d love to be able to express the resonance in terms of Q factor, just like in reson~ or filtergraph~ …

can anyone enlighten me on this subject, or point me towards some on-line resource???

thank you!

Dec 05 2009 | 5:40 pm


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Forums > MaxMSP