firwin.m

Matlab时频分析工具箱,希望能对大家有所帮助啊

function g=firwin(name,M,centering);
%FIRWIN  FIR window
%   Usage:  g=firwin(name,M);
%           g=firwin(name,M,centering);
%
%   FIRWIN(name,M) will return a FIR window of length M of type
%   name.
%
%   FIRWIN(name,M,centering) will create a window centered as 
%   specified by centering. The default (centering=0) is to return
%   a whole-point centered window, while a value of .5 will produce a
%   half-point even function (traditional signal processing style).
%
%   The windows are normalized, such that if used for Gabor systems
%   with parameters a=M/2 and M, they will generate Gabor frames
%   with framebounds close to 1.
%
%   All windows are symmetric and can be used for Wilson bases, except
%   when noted otherwise. 
%
%   The windows available are:
%
%       hanning - Hanning window. Forms a PU.
%
%       sqrthann - Square root of a Hanning window. Normalized so it
%                 generates a normalized tight Gabor system with parameters
%                 a=M/2 and M or an orthonormal Wilson/MDCT basis with M channels.
%
%       hamming - Hamming window. Forms a PU. This window cannot
%                 be used for a Wilson basis.
%
%       sqrtham - Square root of a Hamming window. As sqrthan.
%
%       blackman - Blackman window
%
%       vorbis  - Iterated sine window. This is a tight window.
% 
%   SEE ALSO:  PGAUSS, PBSPLINE, FIRKAISER
%
%   REFERENCES:
%     A. V. Oppenheim and R. W. Schafer. Discrete-time signal processing.
%     Prentice Hall, Englewood Cliffs, NJ, 1989.
%     

% 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(2,3,nargin));

if nargin==2
  centering=0;
end;

name=lower(name);

% This is the normally used sampling vector.
x=((0:M-1)'+centering)/M;
switch name
  case {'hanning'}
    g=(0.5+0.5*cos(2*pi*x));

  case {'sqrthan','sqrthann'}
    g=sqrt(firwin('hanning',M,centering))/sqrt(M/2);

  case {'hamming'}
    g=0.54-0.46*cos(2*pi*(x-.5));

  case {'sqrtham'}
    g=sqrt(firwin('hamming',M,centering)/1.08)/sqrt(M);

  case {'blackman'}
    g=0.42-0.5*cos(2*pi*(x-.5))+0.08*cos(4*pi*(x-.5));

  case {'vorbis'}
    g=sin(pi/2*sin(pi*(x-.5).^2))/sqrt(M);

  otherwise
    error('Unknown window.');
end;