[PD] biquad~ formula

[Nicolas Lhommet]

Hello,
biquad~ formula in the PD help-patch is :
y(n) = ff1 * w(n) + ff2 * w(n-1) + ff3 * w(n-2)
w(n) = x(n) + fb1 * w(n-1) + fb2 * w(n-2)

biquad~ formula in Jmax is :
y[n] = c1*x[n] + c2*x[n-1] + c3*x[n-2] - c4*y[n-1] - c5*y[n-2]

What is the mathematical relation between these two formulae (so between Pd
and Jmax coefficients) ?

I found a nice document that explains how to get the right coeffs for
different filters :
http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt
and I'm not sure how to use it with PD biquad~ object.

nicolas