spec2.m

该工具箱为时频分析中的一类重要变换,离散时频分布的工具箱,其中提供基本算法的程序.可直接应用

function [tfd, t, f] = spec2(x, fs, nfreq, decf, w, how)
% spec2 -- Compute samples of the type II spectrogram.
%
%  Usage
%    [tfd, t, f] = spec2(x, fs, nfreq, decf, w, how)
%
%  Inputs
%    x      signal vector
%    fs     sampling frequency of x (optional, default is 1 sample/second)
%    nfreq  number of samples to compute in frequency (optional, default
%           is 256)
%    decf   sub-sampling factor in time of the stft (optional, default 
%           is 1, i.e. no sub-sampling)
%    w      if length(w)==1 then the window is a guassian with duration 'w'
%           (see chirplets.m), otherwise 'w' is the window.  'w' must have an
%           odd length to have a center point. (optional, default is a 
%           gaussian with a duration of 5)
%    how    if how='short' then the stft is computed for the same times
%           as the signal and 
%               size(tfd,2) = length(x)
%           if how='long' then the stft will be computed for times before
%           and after the times of the signal and
%               size(tfd,2) = length(x) + length(w) - 1
%           (optional, default is 'short')
%
%  Outputs
%    tfd  matrix containing the spectrogram of signal x (optional)
%    t    vector of sampling times (optional)
%    f    vector of frequency values (optional)
%
% If no output arguments are specified, then the spectrogram is
% displayed using ptfd(tfd, t, f).

% Copyright (C) -- see DiscreteTFDs/Copyright

error(nargchk(1, 6, nargin));
if (nargin == 1)
  [tfd, t, f] = stft2(x);
elseif (nargin == 2)
  [tfd, t, f] = stft2(x, fs);
elseif (nargin == 3)
  [tfd, t, f] = stft2(x, fs, nfreq);
elseif (nargin == 4)
  [tfd, t, f] = stft2(x, fs, nfreq, decf);
elseif (nargin == 5)
  [tfd, t, f] = stft2(x, fs, nfreq, decf, w);
elseif (nargin == 6)
  [tfd, t, f] = stft2(x, fs, nfreq, decf, w, how);
end

tfd = real(tfd.*conj(tfd));

if (nargout == 0)
  ptfd(tfd, t, f);
  clear tfd
end