Generating sound in C

Hello,

I would like to ask some advice on optimizing this function, that I want
to 
use to generate sound with waveOutOpen. I will just bluntly post it and
hope 
that some bright expert ****nes her/his light on it:

VOID FillBuffer (PBYTE pBuffer)
{
     static double fAngle[MAX_CH] ;   // Phasenwinkel
     static LONG          i, j ;
  static double dTmpL, dTmpR ;
     short iValueL, iValueR ;

  // Generate the sound data
  for (i = 0 ; i < OUT_BUFFER_SIZE / 4 ; i++)
     {
        dTmp=0 ;

        for (j = 0 ; j < siNChannels ; j++)
        {
            dTmp += dblVol[j] * sin (fAngle[j] + dblPhase[j]) ;
            fAngle[j] +=  dblFreq[j] ;
            if (fAngle[j] > PIx2) fAngle[j] -= PIx2 ;
        }

     // Average the siNChannels sines, apply master volume and panning
     dTmp = dblVolume * dTmp / siNChannels ;


     if (dblPan[j]<0) // -1 is left channel, 1 right channel
        {
            dTmpL= dTmp ;
         dTmpR = dTmp * (1.0 + dblPan[j]) ;
        } else {
            dTmpL= dTmp * (1.0 - dblPan[j]) ;
         dTmpR = dTmp ;
        }

        iValueL = (short) (32767 * dTmpL) ;
        iValueR = (short) (32767 * dTmpR) ;

        pBuffer [i * 4] = (BYTE) (iValueL & 0x00ff) ;
        pBuffer [i * 4 + 1] = (BYTE) ((iValueL& 0xff00) / 0x100);
        pBuffer [i * 4 + 2] = (BYTE) (iValueR & 0x00ff) ;
        pBuffer [i * 4 + 3] = (BYTE) ((iValueR & 0xff00) / 0x100);
     }
}

Thank you very much!

Marc.