demo_spectrogram.py: added simple spectrogram demo

diff --git a/interfaces/python/demo_spectrogram.py b/interfaces/python/demo_spectrogram.py
new file mode 100755 (executable)
index 0000000..52402c8
--- /dev/null
+++ b/interfaces/python/demo_spectrogram.py
@@ -0,0 +1,41 @@
+#! /usr/bin/python
+
+import sys
+from aubio import pvoc, source
+from numpy import array, arange, zeros, shape, log10, vstack
+from pylab import imshow, show, gray, autumn, axis, ylabel, xlabel, xticks, yticks
+
+def get_spectrogram(filename):
+  win_s = 512                 # fft size
+  hop_s = win_s / 2           # hop size
+  fft_s = win_s / 2 + 1       # number of spectrum bins
+  samplerate = 16000
+  specgram = zeros([0, fft_s], dtype='float32')
+  a = source(filename, samplerate, hop_s)                 # mono 8kHz only please
+  pv = pvoc(win_s, hop_s)                            # phase vocoder
+  while True:
+    samples, read = a()                              # read file
+    #specgram = vstack((specgram,1.-log10(1.+pv(samples).norm)))   # store new norm vector
+    specgram = vstack((specgram,pv(samples).norm))   # store new norm vector
+    if read < a.hop_size: break
+
+  autumn()
+  from pylab import gray
+  gray()
+  imshow(specgram.T, origin = 'bottom', aspect = 'auto')
+  axis([0, len(specgram), 0, len(specgram[0])])
+  ylabel('Frequency (Hz)')
+  xlabel('Time (s)')
+  time_step = hop_s / float(samplerate)
+  total_time = len(specgram) * time_step
+  ticks = 10
+  xticks( arange(ticks) / float(ticks) * len(specgram),
+      [x * total_time / float(ticks) for x in range(ticks) ] )
+  yticks( arange(ticks) / float(ticks) * len(specgram[0]),
+      [x * samplerate / 2. / float(ticks) for x in range(ticks) ] )
+  show()
+
+if len(sys.argv) < 2:
+  print "Usage: %s <filename>" % sys.argv[0]
+else:
+  [get_spectrogram(soundfile) for soundfile in sys.argv[1:]]