python/demos/demo_alsa.py: add example using alsaaudio (closes #72)

diff --git a/python/demos/demo_alsa.py b/python/demos/demo_alsa.py
new file mode 100755 (executable)
index 0000000..cd58a33
--- /dev/null
+++ b/python/demos/demo_alsa.py
@@ -0,0 +1,45 @@
+#! /usr/bin/env python
+
+import alsaaudio
+import numpy as np
+import aubio
+
+# constants
+samplerate = 44100
+win_s = 2048
+hop_s = win_s // 2
+framesize = hop_s
+
+# set up audio input
+recorder = alsaaudio.PCM(type=alsaaudio.PCM_CAPTURE)
+recorder.setperiodsize(framesize)
+recorder.setrate(samplerate)
+recorder.setformat(alsaaudio.PCM_FORMAT_FLOAT_LE)
+recorder.setchannels(1)
+
+# create aubio pitch detection (first argument is method, "default" is
+# "yinfft", can also be "yin", "mcomb", fcomb", "schmitt").
+pitcher = aubio.pitch("default", win_s, hop_s, samplerate)
+# set output unit (can be 'midi', 'cent', 'Hz', ...)
+pitcher.set_unit("Hz")
+# ignore frames under this level (dB)
+pitcher.set_silence(-40)
+
+print("Starting to listen, press Ctrl+C to stop")
+
+# main loop
+while True:
+    try:
+        # read data from audio input
+        _, data = recorder.read()
+        # convert data to aubio float samples
+        samples = np.fromstring(data, dtype=aubio.float_type)
+        # pitch of current frame
+        freq = pitcher(samples)[0]
+        # compute energy of current block
+        energy = np.sum(samples**2)/len(samples)
+        # do something with the results
+        print("{:10.4f} {:10.4f}".format(freq,energy))
+    except KeyboardInterrupt:
+        print("Ctrl+C pressed, exiting")
+        break