chore: move examples to dedicated directory

examples/isine.py

@@ -0,0 +1,97 @@
+''' Use this example from an interactive python session, for example:
+
+>>> from isine import change
+>>> change(880)
+'''
+
+from __future__ import print_function
+
+import sys
+import time
+from threading import Thread
+from multiprocessing import Queue
+
+if sys.version_info[0] < 3:
+    from Queue import Empty
+else:
+    from queue import Empty
+
+from math import pi, sin, ceil
+import struct
+import itertools
+import alsaaudio
+
+sampling_rate = 48000
+
+format = alsaaudio.PCM_FORMAT_S16_LE
+pack_format = 'h'  # short int, matching S16
+channels = 2
+
+def nearest_frequency(frequency):
+    # calculate the nearest frequency where the wave form fits into the buffer
+    # in other words, select f so that sampling_rate/f is an integer
+    return float(sampling_rate)/int(sampling_rate/frequency)
+
+def generate(frequency, duration = 0.125):
+    # generate a buffer with a sine wave of `frequency`
+    # that is approximately `duration` seconds long
+
+    # the length of a full sine wave at the frequency
+    cycle_size = int(sampling_rate / frequency)
+
+    # number of full cycles we can fit into the duration
+    factor = int(ceil(duration * frequency))
+
+    # total number of frames
+    size = cycle_size * factor
+
+    sine = [ int(32767 * sin(2 * pi * frequency * i / sampling_rate)) \
+             for i in range(size)]
+
+    if channels > 1:
+        sine = list(itertools.chain.from_iterable(itertools.repeat(x, channels) for x in sine))
+
+    return struct.pack(str(size * channels) + pack_format, *sine)
+
+
+class SinePlayer(Thread):
+
+    def __init__(self, frequency = 440.0):
+        Thread.__init__(self, daemon=True)
+        self.device = alsaaudio.PCM(channels=channels, format=format, rate=sampling_rate)
+        self.queue = Queue()
+        self.change(frequency)
+
+    def change(self, frequency):
+        '''This is called outside of the player thread'''
+        # we generate the buffer in the calling thread for less
+        # latency when switching frequencies
+
+        if frequency > sampling_rate / 2:
+            raise ValueError('maximum frequency is %d' % (sampling_rate / 2))
+
+        f = nearest_frequency(frequency)
+        print('nearest frequency: %f' % f)
+
+        buf = generate(f)
+        self.queue.put(buf)
+
+    def run(self):
+        buffer = None
+        while True:
+            try:
+                buffer = self.queue.get(False)
+            except Empty:
+                pass
+            if buffer:
+                if self.device.write(buffer) < 0:
+                    print("Playback buffer underrun! Continuing nonetheless ...")
+
+
+isine = SinePlayer()
+isine.start()
+
+time.sleep(1)
+isine.change(1000)
+time.sleep(1)
+