From: drowe67 <drowe67@01035d8c-6547-0410-b346-abe4f91aad63>
Date: Sun, 29 Apr 2018 05:26:27 +0000 (+0000)
Subject: working spectrogram
X-Git-Url: http://git.whiteaudio.com/gitweb/?a=commitdiff_plain;h=482465bde563decd258568b723938332bf6d2895;p=freetel-svn-tracking.git

working spectrogram

git-svn-id: https://svn.code.sf.net/p/freetel/code@3533 01035d8c-6547-0410-b346-abe4f91aad63
---

diff --git a/codec2-dev/octave/plot_specgram.m b/codec2-dev/octave/plot_specgram.m
index 480253eb..adb50d6c 100644
--- a/codec2-dev/octave/plot_specgram.m
+++ b/codec2-dev/octave/plot_specgram.m
@@ -3,28 +3,18 @@
 %
 % As the name suggests.....
 
-
 function S = plot_specgram(x)
 
-  % set step size so we end up with an aray of pixels that is square.  Otherwise
-  % imagesc will only use a ribbon on the figure.
-
   Fs = 8000;
-  l = length(x);
-
-  Nfft = 512; Nfft2 = Nfft/2; window = 512; nstep = window/2;
-  nsamples = floor(l/nstep) - 1;
-  S = zeros(nsamples,Nfft);
-  h = hanning(Nfft);
-  for i=1:nsamples
-    st = (i-1)*nstep+1; en = st+window-1;
-    %printf("i: %d st: %d en: %d l: %d\n", i, st, en, l);
-    S(i,:) = 20*log10(abs(fft(x(st:en).*h')));
-  end
-  mx = ceil(max(max(S))/10)*10;
-  S = max(S,mx-30);
-  mesh((1:Nfft2)*4000/Nfft2, (1:nsamples)*nstep, S(:,1:Nfft2));
-  view(90,-90);
-  %xlabel('Frequency (Hz)');
-  %ylabel('Sample');
-en
+  
+  step = fix(20*Fs/1000);     # one spectral slice every 5 ms
+  window = fix(160*Fs/1000);  # 40 ms data window
+  fftn = 2^nextpow2(window); # next highest power of 2
+  [S, f, t] = specgram(x, fftn, Fs, window, window-step);
+  S = abs(S(2:fftn*4000/Fs,:)); # magnitude in range 0<f<=4000 Hz.
+  S = S/max(S(:));           # normalize magnitude so that max is 0 dB.
+  S = max(S, 10^(-20/10));   # clip below -20 dB.
+  S = min(S, 10^(-3/10));    # clip above -3 dB.
+  imagesc (t, f, log(S));    # display in log scale
+  set (gca, "ydir", "normal"); # put the 'y' direction in the correct direction
+endfunction