[Speex-dev] Integrating speex with VideoNet application: Constantbackground noise

John Miles jmiles at pop.net
Wed Nov 1 22:04:39 PST 2006

At first glance it looks like you are opening the output device in 8-bit
mode (m_waveFormatEx.wBitsPerSample =8;).  You will need to use 16-bit mode
if you expect to write an array of signed short integers to the audio
buffer.  8-bit PCM is an unsigned mode, no longer used much these days.

Also, a good debugging trick is to include something like this in your
output sample processing loop:

    static FILE *hack = fopen("test.raw","wb");
    fwrite(output, 2, FRAME_SIZE, hack);

After your app is closed, there will be a file called "test.raw" in its
working directory, which you can load into Sound Forge or a similar audio
editing package for closer inspection without relying on your output buffers
and playback code to work properly.

-- john
RAD Game Tools
  -----Original Message-----
  From: speex-dev-bounces at xiph.org [mailto:speex-dev-bounces at xiph.org]On
Behalf Of Carine Liang
  Sent: Wednesday, November 01, 2006 9:40 PM
  To: speex-dev at xiph.org
  Subject: Re: [Speex-dev] Integrating speex with VideoNet application:
Constantbackground noise


  Can someone please help me with my problem below. Any suggestions is


  ----- Original Message ----
  From: Carine Liang <carineliang at yahoo.com.sg>
  To: speex-dev at xiph.org; speex-dev at xiph.org
  Sent: Tuesday, 31 October 2006 1:05:49 PM
  Subject: [Speex-dev] Integrating speex with VideoNet application: Constant
background noise


  I am developing a peer-to-peer video conference application which uses
speex as a codec for the voice.

  I am new to speex, so please bear with me if I asked the obvious. After I
added the encode and decode function to my MFC app, I heard a constant
background noise, even when no one is speaking into the microphone.

  #define FRAME_SIZE 160

  The application is coded in MFC C++. The record buffer is set to be the
same as the FRAME_SIZE such that my callback function is called everytime
160 bytes of data is recorded.

  Here's what I did in the initialisation (called only once).
  m_waveFormatEx.wFormatTag =WAVE_FORMAT_PCM;
  m_waveFormatEx.nChannels =1;
  m_waveFormatEx.wBitsPerSample =8;
  m_waveFormatEx.cbSize =0;
  m_waveFormatEx.nSamplesPerSec = 8000;
  m_waveFormatEx.nBlockAlign =1;
  m_waveFormatEx.nAvgBytesPerSec = 8000;

  int quality =8;
  enc_state = speex_encoder_init(&speex_nb_mode);
  speex_encoder_ctl(enc_state, SPEEX_SET_QUALITY, &quality);

  In my recording callback function
  LRESULT RecordSound::OnSoundData(WPARAM wParam, LPARAM lParam)
      dataPtr = (char *)lpHdr ->lpData;
      dataSize = (int)lpHdr ->dwBytesRecorded;

      for(int k=0;k<FRAME_SIZE;k++)
         input[k] = dataPtr[k];     //input is float[FRAME_SIZE]

      speex_encode(enc_state, input, &bits);
      encByte = speex_bits_write(&bits, cbits, 200);

      //send cbits to peer computer via sockets

  In the receiver's initialization function, I've initialized the
  dec_state = speex_decoder_init(&speex_nb_mode);

  In the receiver's socket function, it reads from socket and store the data
in cbits (char array).
      speex_bits_read_from(&bits, cbits, retvalue); //retvalue is 38
      speex_decode(dec_state, &bits, output); //where output is float array

      for(int k=0;k<FRAME_SIZE;k++)
         out[k] = output[k];  //out is a char array


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