magresp.m

linear time－frequency toolbox

function magresp(g,L,donf);
%MAGRESP   Magnitude response plot of TF-transform
%   Usage:   magresp(g);
%            magresp(g,L);
%            magresp(g,L,'nf');
%
%   MAGRESP(g) will display the magnitude response of the window g.
%   This is the DFT of g shown on a log scale normalized such that
%   the peak is 0 db.
%
%   MAGRESP(g,L) does the same, but extends the window to length L.
%   Always use this mode for FIR windows, and select an L somewhat
%   longer than the window to make an accurate plot.
%
%   If the input window is real, only the positive frequencies will be
%   shown. MAGRESP(g,L,'nf') will show the negative frequencies anyway.


error(nargchk(1,3,nargin));

if nargin<2
  L=length(g);
end;

g=firextend(g,L);

% Perform unitaty DFT.
FF=abs(fft(g))/sqrt(L);

% Scale
FF=FF/max(max(abs(FF)));

% Convert to Db. Add eps to avoid log of zero.
FF=20*log10(FF+eps);

ymin=max(-100,min(min(FF)));

donf=0;
if iscomplex(g)
  donf=1;
end;
if nargin==3
  donf=1;
end;

if donf
  xrange=-floor(L/2):ceil(L/2)-1;
  plotff=fftshift(FF);
  axisvec=[-L/2 L/2 ymin 0];
else
  % Only plot positive frequencies for real-valued signals.
  xrange=0:floor(L/2);
  axisvec=[0 L/2 ymin 0];
  plotff=FF(1:floor(L/2)+1);
end;

plot(xrange,plotff);
axis(axisvec);
xlabel('Frequency');
ylabel('Db');
legend('off');