Damian Stewart wrote: > Charles Henry wrote: > >> There is no zero at z=0. I'm not sure about this one--but it seems as >> though it's impossible to have a zero at z=0?
a zero at z=0 is a delay of 1 sample, so in: y = a x(0) + b x(-1) + c x(-2) + d y(-1) + e y(-2) there is a zero at z=0 if a == 0, and two zeros at z=0 if a == 0 and b == 0 (iirc) > [shrug] i don't even know what a 'zero' is. and that's after reading > several different webpages that attempted to explain biquad filtering to > me. i just don't understand it. if you have a transfer function like: (z-a)(z-b) H(z) = g ---------- (z-c)(z-d) then 'a' and 'b' are zeros and 'c' and 'd' are poles. The gain+phase response at a given frequency f is given by: H( exp(i w) ) = H( cos(w) + i sin (w) ) where w = 2 * pi * f / SR Intuitively the closer the point exp(iw) is to a zero, the less the gain (and if it's equal to a zero the gain is zero), and the closer the point is to a pole, the greater the gain (and if it's equal to a pole, the gain is infinite - so keep pole radius strictly less than 1 !). Claude -- http://claudiusmaximus.goto10.org _______________________________________________ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list