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Dear Sirs...

I am trying to create a simple voip application using android. The settings are as follows:

1- Two android machines are being used: A phone, and a tablet.
2- Both machines are connected via "Wi-Fi Direct"
3- The connectivity is working perfectly fine and I can send and receive data without a problem
4- Each few milliseconds I get the contents of the recording buffer, and send it from the client to the server. No compression is being applied here. I just want to send raw audio samples for now.
5- the samples are played on the other device and I can distinguish that the speech is being transmitted however the noise is very high, so I am not sure what the reason is.

I the code of the client and server threads is shown below. I am sure there are things that I am missing here, so any advice is highly appreciated. I don't want to use an SDK, or anything else, I just want to identify what the problem is.

Thank you


public void run() 
{
  try
  {
    // open connection with the server
    InetAddress serverAddr = InetAddress.getByName(this.ServerIPEditText.getText().toString());
    int port=Integer.parseInt(this.ServerPortEditText.getText().toString());
    Socket socket = new Socket(serverAddr, port);
    OutputStream ServerStream=socket.getOutputStream();
			
    // prepare mic recordings
    AudioRecord recorder = new AudioRecord(MediaRecorder.AudioSource.MIC,
        RECORDER_SAMPLERATE, RECORDER_CHANNELS,
	RECORDER_AUDIO_ENCODING,  RECORDER_SAMPLERATE * 4);
				
    recorder.startRecording();
			
    short[] buffer=new short[RECORDER_SAMPLERATE*4];
    ByteBuffer byteBuf = ByteBuffer.allocate(2*RECORDER_SAMPLERATE*4);
			
    // keep recording and sending to the server
    while (true)
    {
				
      // first wait for parts of a second, for example 128ms
      Thread.sleep(128);
				
      // read the recorded data
      int count=recorder.read(buffer, 0, buffer.length);
				
      // convert shorts into bytes
      byteBuf.rewind();
      for(int i=0;i<count;i++)
        byteBuf.putShort(buffer[i]);
				
      int length=count*2;
				
			
      // send data
      ServerStream.write(byteBuf.array(),0,length);
				
      ServerStream.flush(); 
    }
  }
  catch (Exception e)
  {
    e.printStackTrace();
  }
		
}


Server thread:

public void run() 
{
  try 
  {
    // accept client connection
    Socket client=this.MyServerSocket.accept();
    InputStream ClientStream=client.getInputStream();
			
    // now prepare stuff to be played
    short[] buffer=new short[RECORDER_SAMPLERATE*4];
    ByteBuffer byteBuf = ByteBuffer.allocate(2*RECORDER_SAMPLERATE*4);

			
    // prepare audio player
    int intSize = android.media.AudioTrack.getMinBufferSize(RECORDER_SAMPLERATE, RECORDER_CHANNELS, RECORDER_AUDIO_ENCODING); 
    AudioTrack at = new AudioTrack(AudioManager.STREAM_MUSIC, 
                    RECORDER_SAMPLERATE, AudioFormat.CHANNEL_CONFIGURATION_MONO,
                    AudioFormat.ENCODING_PCM_16BIT, 44100*4, AudioTrack.MODE_STREAM); 
    at.play();

    byte[] readBuffer=new byte[1024*4];

	        
    // enter a loop
    while (true)
    {
      // set the length of bytes to be read
      int length=readBuffer.length;
				
      // read the chunk of PCM audio
      int pos=0;
      while (pos!=length)
      {
        pos+=ClientStream.read(readBuffer,pos,length-pos);
      }
				
      //now convert that into short array
      for(int i=0;i<length/2;i++)
      {
        int v=readBuffer[i*2]+readBuffer[i*2+1]-32768;
        buffer[i]=(short) v;
      }
				
				 
      // send this to the out buffer
      at.write(buffer, 0, length/2); 
				
				
    }
			
  } 
  catch (IOException e) 
  {
    // TODO Auto-generated catch block
    e.printStackTrace();
  }
		  
}
Posted
Updated 24-Jun-13 2:58am
v2

1 solution

Hi there...

I figured out the solution. First the way I used to convert values back from short to byte is totally wrong. In addition I had an impression that byte value in java is from 0 to 255, however it is from -128 to +127


so I had to modify the client, and just pass the array at the server without any modification and it played perfectly well.

the modification at the client is - converting short into byte array -:

C#
for(int i=0;i<count;i++)
{
    tmp=buffer[i]+32768;
    b1= tmp % 256;
    b2= tmp / 256;
    bbuf[i*2  ]=(byte) (b1-128);
    bbuf[i*2+1]=(byte) (b2-128);
}


as for the server just pass the array directly to the player and it should work perfectly fine.
   

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