wolffd@0: % filter = SecondOrderFilter(f, q, fs)
wolffd@0: % Design a second order digital filter with a center frequency of
wolffd@0: % f, filter quality of q, and digital sampling rate of fs (Hz).
wolffd@0: 
wolffd@0: % (c) 1998 Interval Research Corporation  
wolffd@0: 
wolffd@0: function filts = SecondOrderFilter(f,q,fs)
wolffd@0: cft = f'/fs;
wolffd@0: rho = exp(- pi * cft ./ q');
wolffd@0: theta = 2 * pi * cft .* sqrt(1-1 ./(4*q'.^2));
wolffd@0: filts = [ ones(size(rho)) -2*rho.*cos(theta) rho.^2 ];