block_dc.c

DSP tms320c6713: detection play audio signal

//Block the DC in input signal.
//sample = current sample of input signal (16-bit:S15-bit)
//returns sample - DC (16-bit)

#define dc_coeff 10   				  //coefficient for the DC blocking filter
int dc = 0;           				  //current DC estimate (32-bit: SS30-bit)
short block_dc(short sample)
{
  short word1,word2;

  if (dc < 0) {
    word1 = -((-dc) >> 15);         		//retain the sign when DC < 0
  	word2 = -((-dc) & 0x00007fff);
  }
  else {
  	word1 = dc >> 15;         					//word1=high-order 15-bit word of dc
    word2 = dc & 0x00007fff; 			 		//word2=low-order 15-bit word of dc
  }
  dc = word1 * (32768 - dc_coeff) + 
  	   ((word2 * (32768 - dc_coeff)) >> 15) + 
  	   sample * dc_coeff;     					//dc=dc*(1-coeff) + sample*coeff
  return sample - (dc >> 15); 				//return sample - dc
}