playwav uses PCM_FORMAT_U8 for 8bit data.

Added isine as an example for interactive generation of sound.


git-svn-id: svn://svn.code.sf.net/p/pyalsaaudio/code/trunk@33 ec2f30ec-7544-0410-870e-f70ca00c83f0

CHANGES

@@ -3,6 +3,7 @@ Version 0.5:
   This included a mixertest with more features
 - fixed/applied patch 2594366: alsapcm_setup does not do any error checking
 
+
 Version 0.4:
 - API changes: mixers() and Mixer() now take a card index instead of a 
   card name as optional parameter.

isine.py

@@ -0,0 +1,79 @@
+''' Use this example from an interactive python session, for example:
+
+>>> from isine import change
+>>> change(880)
+'''
+
+from threading import Thread
+from Queue import Queue, Empty
+from math import pi, sin
+import struct
+import alsaaudio
+
+sampling_rate = 44100
+format = alsaaudio.PCM_FORMAT_S16_LE
+framesize = 2 # bytes per frame for the values above
+
+def digitize(s):
+    if s > 1.0 or s < -1.0:
+        raise ValueError
+        
+    return struct.pack('h', int(s * 32767)) 
+
+def generate(frequency):
+    # generate a buffer with a sine wave of frequency
+    size = int(sampling_rate / frequency)
+    buffer = ''
+    for i in range(size):
+        buffer = buffer + digitize(sin(i/(2 * pi)))
+
+    return buffer
+
+class SinePlayer(Thread):
+    
+    def __init__(self, frequency = 440.0):
+        Thread.__init__(self)
+        self.setDaemon(True)
+        self.device = alsaaudio.PCM()
+        self.device.setchannels(1)
+        self.device.setformat(format)
+        self.device.setrate(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
+        
+
+        # More than 100 writes/s are pushing it - play multiple buffers
+        # for higher frequencies
+
+        factor = int(frequency/100.0)
+        if factor == 0:
+            factor = 1
+        
+        buf = generate(frequency) * factor
+        print 'factor: %d, frames: %d' % (factor, len(buf) / framesize)
+
+        self.queue.put( buf)
+                        
+    def run(self):
+        buffer = None
+        while True:
+            try:
+                buffer = self.queue.get(False)
+                self.device.setperiodsize(len(buffer) / framesize)
+                self.device.write(buffer)
+            except Empty:
+                if buffer:
+                    self.device.write(buffer)
+                
+
+isine = SinePlayer()
+isine.start()
+
+def change(f):
+    isine.change(f)
+    

playwav.py

@@ -14,13 +14,18 @@ import alsaaudio
 
 def play(device, f):    
 
+
+    sys.stdout.write('%d channels, %d sampling rate\n' % (f.getnchannels(),
+                                                          f.getframerate()))
     # Set attributes
     device.setchannels(f.getnchannels())
     device.setrate(f.getframerate())
 
-    # We assume signed data, little endian
+
+    # We 8bit is unsigned in wav files
     if f.getsampwidth() == 1:
-        device.setformat(alsaaudio.PCM_FORMAT_S8)
+        device.setformat(alsaaudio.PCM_FORMAT_U8)
+    # Otherwise we assume signed data, little endian
     elif f.getsampwidth() == 2:
         device.setformat(alsaaudio.PCM_FORMAT_S16_LE)
     elif f.getsampwidth() == 3: