windows.m

语音信号处理matlab工具箱源码

function w = windows(wtype,n,mode,p)
%WINDOWS Generate a standard windowing function (TYPE,N,MODE,P)
%
%	TYPE	is one of:
%
%			'blackman'
%			'kaiser'	   with parameter P (often called beta) (default P=8)
%			'gaussian'	truncated at +-P std deviations (default P=3)
%			'hamming'
%			'hanning'
%			'harris3'	3-term balckman-harris with 67dB sidelobes
%			'harris4'	4-term balckman-harris with 92dB sidelobes
%			'rectangle'
%			'triangle'
%
%	   N is either the number of points to generate. If N>1 is
%		a non-integer, then FLOOR(N) points will be generated.
%
%	   MODE determines the scaling and sampling of the window function and
%     is a text string with up to 3 characters whose meanings are given below. The
%     default is 'ubw' for window functions whose end points are non-zero and 'unw'
%     for window functions whose end points are zero (e.g. hanning window)
%
%         scaling:
%                  u = unscaled  with the peak of the underlying continuous
%                      window equalling unity. [default]
%                  p = scaled to make the peak 
%                  d = scaled to make unity DC gain (summed sample values).
%                  e = scaled to make unity energy (summed squared sample values).
%
%         first and last samples:
%                  b = The first and last samples are at the extreme ends of the window [both].
%                  n = The first and last samples are one sample away from the ends of the window [neither].
%                  s = The first and last samples are half a sample away from the ends of the window [shifted].
%                  l = The first sample is at the end of the window while the last is one sample away from the end [left].
%                  r = The first sample is one sample away from the end while the last is at the end of the window [right].
%       
%         whole/half window:
%                  w = The whole window is included [default]
%                  c = The first sample starts in the centre of the window
%                  h = The first sample starts half a sample beyond the centre
%
% For periodic window functions (e.g. hanning, hamming), the underlying period is equal
% to N-1 samples for mode 'b', N+1 samples for mode 'n' and N samples for modes 'l','r'
% and 's' where N is not necessarily an integer (assuming mode 'w' is also selected).
% Overlapping windows normally require that N is an integer and that modes 'l', 'r' or 's'
% are used.

%      Copyright (C) Mike Brookes 2002
%
%      Last modified Wed Jul  2 16:49:44 2003
%
%   VOICEBOX is a MATLAB toolbox for speech processing. Home page is at
%   http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%   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 2 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 can obtain a copy of the GNU General Public License from
%   ftp://prep.ai.mit.edu/pub/gnu/COPYING-2.0 or by writing to
%   Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

kk=[-1 1 1 -1; 0 0 2 -2; 0 1 2 -1;
   -1 0 1 0; 0 0 2 0; 0 1 2 1;
   -1 2 1 0; 0 0 2 -2; 0 1 2 -1;
   -1 1 1 -1; 0 0 2 -2; 0 1 2 -1;
   -1 1 1 1; 0 0 2 0; 0 1 2 1;
   -1 1 1 0; 0 0 2 -1; 0 1 2 0;];  

if nargin<3 | length(mode)==0 | ~ischar(mode)
   mode='uw';
end;
mm=zeros(1,length(mode)+1);
ll='hc lrbns';
for i=1:8
   mm(mode==ll(i))=i-3;
end
wtype=lower(wtype);
k=1+3*max(mm)-min(mm);
if k<4
   switch wtype
   case {'hanning','triangle','blackman'}
      k=k+12;
   end
end

% determine the sample points
fn=floor(n);
v=((0:2:2*fn-2)+(kk(k,1)*fn+kk(k,2)))/(kk(k,3)*n+kk(k,4));

% now make the window
np=0;
switch wtype
case 'hanning'
  w = 0.5+0.5*cos(pi*v);

case 'rectangle'
  w = ones(size(v));

case 'triangle'
  w = 1-abs(v);

case 'gaussian'
  if nargin<4, p=3; end;
  w=exp(-0.5*p(1)^2*(v.*v));
  np=1;

case 'kaiser'
  if nargin<4, p=8; end;
  w=besseli(0,p*sqrt(1-v.^2))/besseli(0,p(1));
  np=1;

case 'hamming'
  w = 0.54+0.46*cos(pi*v);

case 'blackman'
  w = 0.42+0.5*cos(pi*v) + 0.08*cos(2*pi*v);

case 'harris3'
  w = 0.42323 + 0.49755*cos(pi*v) + 0.07922*cos(2*pi*v);

case 'harris4'
  w = 0.35875 + 0.48829*cos(pi*v) + 0.14128*cos(2*pi*v) + 0.01168*cos(3*pi*v);
otherwise
   error(sprintf('Unknown window type: %s', wtype));
end;

% scale if required
if any(mode=='d')
   w=w/sum(w);
elseif any(mode=='e')
   w=w/sqrt(sum(w.^2));
elseif any(mode=='p')
   w=w/max(w);
end

if ~nargout
   plot(w);
   if np>0
         title(sprintf('%s window (%s ) - mode=''%s''',wtype,sprintf(' %g',p(1:np)),mode));
      else
         title(sprintf('%s window - mode=''%s''',wtype,mode));
         end
end;