Hi John (and Mike),

Just trying out the spectrogram function you wrote.  (Thanks for all the hard work.)  I would like to comment on it.

First off running `help spectrogram` gets the following errors for me.

octave:26> help spectrogram
/tmp/octave-help-Wnvppb:125: misplaced }
/tmp/octave-help-Wnvppb:170: table requires an argument: the formatter for @item
/tmp/octave-help-Wnvppb:187: superfluous argument to @end ifinfo: . (possibly involving @seealso)
/tmp/octave-help-Wnvppb:196: table requires an argument: the formatter for @item
/tmp/octave-help-Wnvppb:199: table requires an argument: the formatter for @item
/tmp/octave-help-Wnvppb:199: no matching `@end table'
/tmp/octave-help-Wnvppb:199: bad argument to @end: @table
/tmp/octave-help-Wnvppb:268: `@end' expected `table', but saw `deftypefn'

Are there some installation instructions I need to follow?  All I did was copy the function to the current working directory and tried to run it.  After the errors, the function description follows.

Next, running without setting the command equal to a variable fails to generate a plot for me.   I tried the first example at https://www.mathworks.com/help/signal/ref/spectrogram.html and I get the following.

octave:27> N = 1024;
octave:28> n = 0:N-1;
octave:29>
octave:29> w0 = 2*pi/5;
octave:30> x = sin(w0*n)+10*sin(2*w0*n);
octave:31> s = spectrogram(x);
octave:32>
octave:32> spectrogram(x,'yaxis')
error: pwelch: string arg 6 illegal value: psd
error: called from
    pwelch at line 442 column 11
    spectrogram at line 235 column 19

How do I generate a plot of the data?

I can try out patches, or new versions if you like.  But next week I am busy, so expect some delays in my response times.  Again thanks for all the hard work you've put into octave and thanks in advance for instructions on how to use spectrogram.

I started working on this function.  I'm attaching my current version for testing and feedback.  There are still some missing features (compute fc and tc outputs?) and probably some bugs.  But the figures it produces look like the ones for the examples in the Matlab online docs for spectrogram now, at least as far as I can tell (to get exact results, you need to use the same colormap).





(file #45155)

According to Matlab documentation

http://de.mathworks.com/help/signal/ref/spectrogram.html

'onesided' — returns the one-sided spectrogram of a real input signal. If nfft is even, then pxx has length nfft/2 + 1 and is computed over the interval [0, π] rad/sample. If nfft is odd, then pxx has length (nfft + 1)/2 and the interval is [0, π) rad/sample. If you specify fs, then the intervals are respectively [0, fs/2] cycles/unit time and [0, fs/2) cycles/unit time.

specgram must return 257 points for nfft = 512. The current code returns 256 points only.

The suggested change is:

  if rem(n,2)==1
      ret_n = (n+1)/2;
  else
      ret_n = n/2 + 1;
  endif
  S = S(1:ret_n, :);

in specgram.m