Adaptive Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 268

// Adaptnoise_2IN.c Adaptive FIR for sinusoidal noise interference

#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs=DSK6713_AIC23_FREQ_48KHZ; //set sampling rate
#define beta 1E-13 //rate of convergence
#define N 30 //# of weights (coefficients)
#define LEFT 0 //left channel
#define RIGHT 1 //right channel
float w[N]; //weights for adapt filter
float delay[N]; //input buffer to adapt filter
short output; //overall output
short out_type = 1; //output type for slider
volatile union{unsigned int uint; short channel[2];}AIC23_data;

interrupt void c_int11() //ISR

{
short i;
float yn=0, E=0, dplusn=0, desired=0, noise=0;

AIC23_data.uint = input_sample(); //input 32-bit from both channels
desired =(AIC23_data.channel[LEFT]);//input left channel
noise = (AIC23_data.channel[RIGHT]);//input right channel

dplusn = desired + noise; //desired+noise
delay[0] = noise; //noise as input to adapt FIR

for (i = 0; i < N; i++) //to calculate out of adapt FIR
yn += (w[i] * delay[i]); //output of adaptive filter
E = (desired + noise) - 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
}
if(out_type == 1) //if slider in position 1

output=((short)E); //error signal as overall output

else if(out_type==2) //if slider in position 2

output=((short)dplusn); //output (desired+noise)

output_sample(output); //overall output result

return;
}

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 7.17. Adaptive filter program for noise cancellation using external inputs

( adaptnoise_2IN.c ).