[help] FFT & Spectrogram

[Judd Storrs]

On Thu, Jul 2, 2009 at 4:56 AM, febty febriani <febty82 at gmail.com> wrote:

>
> ###
> octave <<EOF
> Fs=1;
> n=4096;
> fh=fopen("result.dat","r");
> y=fscanf(fh,"%lf");
> window=hanning(n);
> y1=(y(1:n)).*(window);
> y2=fft(y1,n*2);
> [S, f, t] = specgram(y, n, Fs, window, length(window)/2);
>
> S=abs(y2(1:n));
> S=S/max(max(S));
> x=((1:n)/n)*(Fs/2);
> subplot(2,1,1);plot(x,S);axis([0
> 0.01]);title("200901");xlabel("Frequency");ylabel("Amplitude");
> subplot(2,1,2);imagesc(flipud(20*log10(S)));
> print -dpng output.png;
> drawnow;
> sleep(10);
> EOF
> ###


I'm not familiar with specgram() but I suspect S is a vector, i.e. 1xN or
Nx1 so the imagesc command complains because S isn't an MxN matrix with both
N>1 and M>1 (i.e. it's a vector not an image(=matrix)).

You can try adding a disp(size(S)) right before the imagesc call to verify
the dimensions.

If you want to display S as an image anyway, I might work to duplicate S to
create a 2xN or Nx2 matrix. i.e. something like

S = repmat(S,[1,2]); # if S is Nx1
S = repmat(S,[2,1]); # if S is 1xN

--judd
-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www-old.cae.wisc.edu/pipermail/help-octave/attachments/20090702/099c9e2d/attachment.html