DGTREAL - Discrete Gabor transform for real-valued signals

Usage

c=dgtreal(f,g,a,M);
c=dgtreal(f,g,a,M,L);
[c,Ls]=dgtreal(f,g,a,M);
[c,Ls]=dgtreal(f,g,a,M,L);

Input parameters

Output parameters

Description

dgtreal(f,g,a,M) computes the Gabor coefficients (also known as a windowed Fourier transform) of the real-valued input signal f with respect to the real-valued window g and parameters a and M. The output is a vector/matrix in a rectangular layout.

As opposed to dgt only the coefficients of the positive frequencies of the output are returned. dgtreal will refuse to work for complex valued input signals.

The length of the transform will be the smallest multiple of a and M that is larger than the signal. f will be zero-extended to the length of the transform. If f is a matrix, the transformation is applied to each column. The length of the transform done can be obtained by L=size(c,2)*a.

The window g may be a vector of numerical values, a text string or a cell array. See the help of gabwin for more details.

dgtreal(f,g,a,M,L) computes the Gabor coefficients as above, but does a transform of length L. f will be cut or zero-extended to length L before the transform is done.

[c,Ls]=dgtreal(f,g,a,M) or [c,Ls]=dgtreal(f,g,a,M,L) additionally returns the length of the input signal f. This is handy for reconstruction:

[c,Ls]=dgtreal(f,g,a,M);
fr=idgtreal(c,gd,a,M,Ls);

will reconstruct the signal f no matter what the length of f is, provided that gd is a dual window of g.

[c,Ls,g]=dgtreal(...) additionally outputs the window used in the transform. This is useful if the window was generated from a description in a string or cell array.

See the help on dgt for the definition of the discrete Gabor transform. This routine will return the coefficients for channel frequencies from 0 to floor(M/2).

dgtreal takes the following flags at the end of the line of input arguments:

dgtreal can be used to manually compute a spectrogram, if you want full control over the parameters and want to capture the output

f=greasy;  % Input test signal
fs=16000;  % The sampling rate of this particular test signal
a=10;      % Downsampling factor in time
M=200;     % Total number of channels, only 101 will be computed

% Compute the coefficients using a 20 ms long Hann window
c=dgtreal(f,{'hann',0.02*fs'},a,M);

% Visualize the coefficients as a spectrogram
dynrange=90; % 90 dB dynamical range for the plotting
plotdgtreal(c,a,M,fs,dynrange);