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!