magresp.m

Matlab时频分析工具箱,希望能对大家有所帮助啊

function magresp(g,varargin);
%MAGRESP   Magnitude response plot of window
%   Usage:   magresp(g,options);
%            magresp(g,L,options);
%            magresp(g,L,sr,options);
%
%   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.
%
%   MAGRESP(g,[],sr) MAGRESP(g,L,sr) will do the same for a window
%   intended to be used with signals with sampling rate sr. The x-axis
%   will display Hz.
%
%   If the input window is real, only the positive frequencies will be
%   shown. Adding the option 'nf' as the last parameter will show the
%   negative frequencies anyway.

% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
% 
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

error(nargchk(1,4,nargin));

L=[];
sr=[];
donf=0;

pcounter=1;
for ii=1:length(varargin)
  if ischar(varargin{ii})
    switch(lower(varargin{ii}))
      case 'nf'
	donf=1;
      otherwise
	error('Unknown option.');
    end;
  end;
  if isnumeric(varargin{ii})
    if pcounter==1
      L=varargin{ii};
    end;
    if pcounter==2
      sr=varargin{ii};
    end;
    pcounter=pcounter+1;
  end;
end;

if isempty(L)
  L=length(g);
end;

g=fir2iir(g,L);

% Perform unitaty DFT.
FF=abs(dft(g));

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

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

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

donf=0;
if ~isreal(g)
  donf=1;
end;

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

plot(xrange,plotff);
axis(axisvec);
ylabel('Magnitude response / Db');

if isempty(sr)
  xlabel('Frequency');
else
  xlabel('Frequency / Hz');
end;

legend('off');