Open-End Reflection Filter Design

N = 1024;
fs = 44100;
c = 340; % sound speed
a = 0.01; % bore radius
omega = 2*pi*[0:N-1]'*fs/2/N;
k = omega/c; zeta = .9;
jka = j.*k.*a;
ZLoZ1 = jka./(zeta + jka);
R = (ZLoZ1 - 1)./(ZLoZ1 + 1);

[Bi,Ai] = invfreqz(R, linspace(0,pi,N), 1,1);
[Bs,As] = stmcb(real(ifft(R)), 1,1);
[Bp,Ap] = prony(real(ifft(R)), 1,1);

Figure 9: Several filter design methods to fit a filter.