wavelet2.m

英文书《Digital Signal Processing with Examples in MATLAB》附带的MATLAB实例

function y=wavelet2(x,Nstgs,Nwts,window)
% y=wavelet2(x,Nstgs,Nwts,window)
%
% Wavelet transform 2: octal bands using QMF stages.
% 
% Inputs:
%   x(1:K) =input signal (converted to a vector).
%            K should be a multiple of 2^Nstgs, or x will be truncated. 
%   Nstgs  =number of stages in the decomposition.
%           (This function produces Nstgs+1 bands in output vector y.)
%	Nwts   =number of weights in FIR filters. Should be odd.
%	window =1 (boxcar),  2 (tapered),  3(tent)  4 (hanning),
%           5 (hamming), 6(blackman), or 7(kaiser) 
%           (In the last case windo is a vector=[7,beta], 
%           with beta in range [4,9].) 
% Output:
%	 y =output vector consisting of low to high bands.
%       Refer to text, fig. 10.26. Suppose length(x)=K=64 and Nstgs=3. 
%       Then y(1:8)=xLLL, y(9:16)=xLLH, y(17:32)=xLH, and y(33:64)=xH.
%
% See also: iwavelet2, wavelet1, iwavelet1, qmf, iqmf
x=col_vec(x);                           %x must be a vector
N=2*floor(Nwts/2)+1;                    %filter size must be odd
M=fix(length(x)/2^Nstgs);               %M =length of shortest output sig.
if M<4,                                 %check if x is large enough
    error('Data vector is too short.')
end
K=M*2^Nstgs;                            %K =length(input)=length(y)
L=K;                                    %L = stage signal length
y=x(1:K);                               %y is initially x(1:K)
for stg=1:Nstgs,                        %for stages 1,2,...,Nstgs
    y(1:L)=qmf(y(1:L),Nwts,window);     %y=[low,high] bands
    L=L/2;                              %next time take the low band
end                                     %finally, y(1:L) =xLLLL...L