title: how to play sound from microphone to speaker directly on android?
body: <p>in my application, I need to direct sound from microphone directly to speaker. No other actions.
  I found a way to direct sound from microphone to earpiece by playing a file and setting speaker off. So I guess speaker can work similarly. However I don' know how to get rid of the playing file thing. Thank you.</p>
  
  <pre><code>speaker() {
      m_audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
      m_audioManager.setSpeakerphoneOn(true);  // not needed I think
      //m_audioManager.setRouting(AudioManager.MODE_NORMAL, AudioManager.ROUTE_EARPIECE, AudioManager.ROUTE_ALL); earpiece need this?
      setVolumeControlStream(AudioManager.STREAM_VOICE_CALL);
      m_audioManager.setMode(AudioManager.MODE_IN_CALL);
  </code></pre>