Adaptive Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 266

// Adaptnoise.c Adaptive FIR filter for noise cancellation

#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs= DSK6713_AIC23_FREQ_8KHZ; //set sampling rate
#include "refnoise.h" //cosine 312 Hz
#include "dplusn.h" //sin(1500) + sin(312)
#define beta 1E-10 //rate of convergence
#define N 30 //# of weights (coefficients)
#define NS 128 //# of output sample points
float w[N]; //buffer weights of adapt filter
float delay[N]; //input buffer to adapt filter
short output; //overall output
short out_type = 1; //output type for slider

interrupt void c_int11() //ISR

{
short i;
static short buffercount=0; //init count of # out samples

float yn, E; //output filter/"error" signal

delay[0] = refnoise[buffercount]; //cos(312Hz) input to adapt FIR
yn = 0; //init output of adapt filter
for (i = 0; i < N; i++) //to calculate out of adapt FIR
yn += (w[i] * delay[i]); //output of adaptive filter
E = dplusn[buffercount] - yn; //"error" signal=(d+n)-yn
for (i = N-1; i >= 0; i--) //to update weights and delays
{
w[i] = w[i] + beta*E*delay[i]; //update weights
delay[i] = delay[i-1]; //update delay samples
}
buffercount++; //increment buffer count
if (buffercount >= NS) //if buffercount=# out samples
buffercount = 0; //reinit count
if (out_type == 1) //if slider in position 1
output = ((short)E*10); //"error" signal overall output
else if (out_type == 2) //if slider in position 2
output=dplusn[buffercount]*10; //desired(1500)+noise(312)
output_sample(output); //overall output result
return;

//return from ISR

}

void main()
{
short T=0;

for (T = 0; T < 30; T++)
{
w[T] = 0; //init buffer for weights

delay[T] = 0; //init buffer for delay samples

}
comm_intr(); //init DSK, codec, McBSP
while(1); //infinite loop
}

FIGURE 7.14. Adaptive FIR filter program for sinusoidal noise cancellation
( adaptnoise.c ).