Finite Impulse Response Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 155

// Notch2.c Two FIR notch filters to remove sinusoidal noise signals

#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ; //set sampling rate
#include "bs900.cof" //BS @ 900 Hz coefficient file
#include "bs2700.cof" //BS @ 2700 Hz coefficient file
short dly1[N]={0}; //delay samples for 1st filter
short dly2[N]={0}; //delay samples for 2nd filter

int y1out = 0, y2out = 0; //init output of each filter

short out_type = 1; //slider for output type

interrupt void c_int11() //ISR

{
short i;
dly1[0] = input_sample(); //newest input @ top of buffer

y1out = 0; //init output of 1st filter

y2out = 0; //init output of 2nd filter

for (i = 0; i< N; i++)
y1out += h900[i]*dly1[i]; //y1(n)+=h900(i)*x(n-i)

dly2[0]=(y1out>>15); //out of 1st filter->in 2nd filter

for (i = 0; i< N; i++)
y2out += h2700[i]*dly2[i]; //y2(n)+=h2700(i)*x(n-i)

for (i = N-1; i > 0; i--) //from bottom of buffer

{
dly1[i] = dly1[i-1]; //update samples of 1st buffer

dly2[i] = dly2[i-1]; //update samples of 2nd buffer

}
if(out_type==1) output_sample(dly1[0]); //corrupted input(voice+sines)
if(out_type==2) output_sample((short)(y2out>>15)); //out of 2nd filter
return; //return from ISR

}

void main()
{

comm_intr(); //init DSK, codec, McBSP

while(1); //infinite loop

}

FIGURE 4.24. Program implementing two FIR notch filters in cascade to remove two unde-
sired sinusoidal signals ( NOTCH2.c ).