Solving problems in software :)

I bought a S/PDIF-analog converter in DealExtreme. It works well, but outputs an annoying buzz when no signal is present. Some say it is a defect, some say it is by design, the converter expects a continous optical signal.

Unfortunately, Mac turns off the optical link when there's no sound for 10 seconds or so. The obvious kludgey solution is to play continously a silence audio stream.

The program below uses CoreAudio to do so. It eats 6% CPU, but nothing is perfect :)

#!/usr/bin/env python

import thread
import coreaudio # http://wiki.python.org/moin/MacPython/CoreAudio
import time

class Ctrl(object):
 def callback(self):
  # called in another thread context!
  return self.silence

 def __init__(self):
  audio_id, sampling_rate, chunksize = coreaudio.initAudio()
  self.silence = [0.0 for i in range(0, chunksize)]
  coreaudio.installAudioCallback(audio_id, self)

 def stop(self):
  coreaudio.stopAudio(self)

# Have to initialize the threading mechanisms in order for PyGIL_Ensure to work
thread.start_new_thread(lambda: None, ())

try:
 ctrl = Ctrl()
 time.sleep(999999)
except KeyboardInterrupt:
 ctrl.stop()
 time.sleep(0.1)

This is actually a nice example of how to use CoreAudio in Python, and it was based in a project of mine, PaiMorse. The start_new_thread is there only to make the interpreter thread-aware, because CoreAudio creates threads unbeknownst to Python.