Damian's Blog .NET from Geneva, Switzerland

private void StartRecording()
{
    _microphone.BufferDuration = TimeSpan.FromMilliseconds(500);

    // Allocate memory to hold the audio data
    _recordingBuffer = new byte[_microphone.GetSampleSizeInBytes(_microphone.BufferDuration)];

    _recordingStream.SetLength(0);

    WriteWavHeader(_recordingStream, _microphone.SampleRate);

    _microphone.Start();
}

private void StopRecording()
{
    _microphone.Stop();
    UpdateWavHeader(_recordingStream);
}

public void WriteWavHeader(Stream stream, int sampleRate)
{
    const int bitsPerSample = 16;
    const int bytesPerSample = bitsPerSample / 8;
    var encoding = System.Text.Encoding.UTF8;

    // ChunkID Contains the letters "RIFF" in ASCII form (0x52494646 big-endian form).
    stream.Write(encoding.GetBytes("RIFF"), 0, 4);

    // NOTE this will be filled in later
    stream.Write(BitConverter.GetBytes(0), 0, 4);

    // Format Contains the letters "WAVE"(0x57415645 big-endian form).
    stream.Write(encoding.GetBytes("WAVE"), 0, 4);

    // Subchunk1ID Contains the letters "fmt " (0x666d7420 big-endian form).
    stream.Write(encoding.GetBytes("fmt "), 0, 4);

    // Subchunk1Size 16 for PCM.  This is the size of therest of the Subchunk which follows this number.
    stream.Write(BitConverter.GetBytes(16), 0, 4);

    // AudioFormat PCM = 1 (i.e. Linear quantization) Values other than 1 indicate some form of compression.
    stream.Write(BitConverter.GetBytes((short)1), 0, 2);

    // NumChannels Mono = 1, Stereo = 2, etc.
    stream.Write(BitConverter.GetBytes((short)1), 0, 2);

    // SampleRate 8000, 44100, etc.
    stream.Write(BitConverter.GetBytes(sampleRate), 0, 4);

    // ByteRate =  SampleRate * NumChannels * BitsPerSample/8
    stream.Write(BitConverter.GetBytes(sampleRate * bytesPerSample), 0, 4);

    // BlockAlign NumChannels * BitsPerSample/8 The number of bytes for one sample including all channels.
    stream.Write(BitConverter.GetBytes((short)(bytesPerSample)), 0, 2);

    // BitsPerSample    8 bits = 8, 16 bits = 16, etc.
    stream.Write(BitConverter.GetBytes((short)(bitsPerSample)), 0, 2);

    // Subchunk2ID Contains the letters "data" (0x64617461 big-endian form).
    stream.Write(encoding.GetBytes("data"), 0, 4);
    
    // NOTE to be filled in later
    stream.Write(BitConverter.GetBytes(0), 0, 4);
}

public void UpdateWavHeader(Stream stream)
{
    if (!stream.CanSeek) throw new Exception("Can't seek stream to update wav header");

    var oldPos = stream.Position;

    // ChunkSize  36 + SubChunk2Size
    stream.Seek(4, SeekOrigin.Begin);
    stream.Write(BitConverter.GetBytes((int)stream.Length - 8), 0, 4);

    // Subchunk2Size == NumSamples * NumChannels * BitsPerSample/8 This is the number of bytes in the data.
    stream.Seek(40, SeekOrigin.Begin);
    stream.Write(BitConverter.GetBytes((int)stream.Length - 44), 0, 4);

    stream.Seek(oldPos, SeekOrigin.Begin);
}