nt_filter_peak

[B,A] = nt_filter_peak(Wo,Q) - second order resonator filter

 Wo: peak frequency (1 == nyquist)
 Q: quality factor

 NoiseTools

0001 function [B,A] = nt_filter_peak(Wo,Q)
0002 %[B,A] = nt_filter_peak(Wo,Q) - second order resonator filter
0003 %
0004 % Wo: peak frequency (1 == nyquist)
0005 % Q: quality factor
0006 %
0007 % NoiseTools
0008 
0009 if nargin<2; error('!'); end
0010 if Wo>1; error('normalized centre frequency should be < 1'); end
0011 
0012 BW=Wo/Q;
0013 
0014 % frequencies are normalized by pi.
0015 BW = BW*pi;
0016 Wo = Wo*pi;
0017 
0018 gain = 1/(1+tan(BW/2));
0019 B  = (1-gain)*[1 0 -1];
0020 A  = [1 -2*gain*cos(Wo) (2*gain-1)];
0021 
0022 if ~nargout
0023     figure(100);
0024     freqz(B,A);
0025     figure(101);
0026     plot([-10:100],filter(B,A,[zeros(10,1);1;zeros(100,1)]));
0027     xlabel('s / sr');
0028 end
0029