sdrangel/dsd/dsd_filters.c

// DMR filter
#define NZEROS 60
float ngain = 7.423339364f;
static float xv[NZEROS+1];
float xcoeffs[] =
{ -0.0083649323f, -0.0265444850f, -0.0428141462f, -0.0537571943f,
-0.0564141052f, -0.0489161045f, -0.0310068662f, -0.0043393881f,
+0.0275375106f, +0.0595423283f, +0.0857543325f, +0.1003565948f,
+0.0986944931f, +0.0782804830f, +0.0395670487f, -0.0136691535f,
-0.0744390415f, -0.1331834575f, -0.1788967208f, -0.2005995448f,
-0.1889627181f, -0.1378439993f, -0.0454976231f, +0.0847488694f,
+0.2444859269f, +0.4209222342f, +0.5982295474f, +0.7593684540f,
+0.8881539892f, +0.9712773915f, +0.9999999166f, +0.9712773915f,
+0.8881539892f, +0.7593684540f, +0.5982295474f, +0.4209222342f,
+0.2444859269f, +0.0847488694f, -0.0454976231f, -0.1378439993f,
-0.1889627181f, -0.2005995448f, -0.1788967208f, -0.1331834575f,
-0.0744390415f, -0.0136691535f, +0.0395670487f, +0.0782804830f,
+0.0986944931f, +0.1003565948f, +0.0857543325f, +0.0595423283f,
+0.0275375106f, -0.0043393881f, -0.0310068662f, -0.0489161045f,
-0.0564141052f, -0.0537571943f, -0.0428141462f, -0.0265444850f,
-0.0083649323f,
};

// NXDN filter
#define NXZEROS 134
float nxgain = 15.95930463f;

static float nxv[NXZEROS+1];

float nxcoeffs[] =
{ +0.031462429f, +0.031747267f, +0.030401148f, +0.027362877f,
+0.022653298f, +0.016379869f, +0.008737200f, +0.000003302f,
-0.009468531f, -0.019262057f, -0.028914291f, -0.037935027f,
-0.045828927f, -0.052119261f, -0.056372283f, -0.058221106f,
-0.057387924f, -0.053703443f, -0.047122444f, -0.037734535f,
-0.025769308f, -0.011595336f, +0.004287292f, +0.021260954f,
+0.038610717f, +0.055550276f, +0.071252765f, +0.084885375f,
+0.095646450f, +0.102803611f, +0.105731303f, +0.103946126f,
+0.097138329f, +0.085197939f, +0.068234131f, +0.046586711f,
+0.020828821f, -0.008239664f, -0.039608255f, -0.072081234f,
-0.104311776f, -0.134843790f, -0.162160200f, -0.184736015f,
-0.201094346f, -0.209863285f, -0.209831516f, -0.200000470f,
-0.179630919f, -0.148282051f, -0.105841323f, -0.052543664f,
+0.011020985f, +0.083912428f, +0.164857408f, +0.252278939f,
+0.344336996f, +0.438979335f, +0.534000832f, +0.627109358f,
+0.715995947f, +0.798406824f, +0.872214756f, +0.935487176f,
+0.986548646f, +1.024035395f, +1.046939951f, +1.054644241f,
+1.046939951f, +1.024035395f, +0.986548646f, +0.935487176f,
+0.872214756f, +0.798406824f, +0.715995947f, +0.627109358f,
+0.534000832f, +0.438979335f, +0.344336996f, +0.252278939f,
+0.164857408f, +0.083912428f, +0.011020985f, -0.052543664f,
-0.105841323f, -0.148282051f, -0.179630919f, -0.200000470f,
-0.209831516f, -0.209863285f, -0.201094346f, -0.184736015f,
-0.162160200f, -0.134843790f, -0.104311776f, -0.072081234f,
-0.039608255f, -0.008239664f, +0.020828821f, +0.046586711f,
+0.068234131f, +0.085197939f, +0.097138329f, +0.103946126f,
+0.105731303f, +0.102803611f, +0.095646450f, +0.084885375f,
+0.071252765f, +0.055550276f, +0.038610717f, +0.021260954f,
+0.004287292f, -0.011595336f, -0.025769308f, -0.037734535f,
-0.047122444f, -0.053703443f, -0.057387924f, -0.058221106f,
-0.056372283f, -0.052119261f, -0.045828927f, -0.037935027f,
-0.028914291f, -0.019262057f, -0.009468531f, +0.000003302f,
+0.008737200f, +0.016379869f, +0.022653298f, +0.027362877f,
+0.030401148f, +0.031747267f, +0.031462429f,
};

short dsd_input_filter(short sample, int mode);

short
dmr_filter(short sample)
{
    return dsd_input_filter(sample, 1);
}

short
nxdn_filter(short sample)
{
    return dsd_input_filter(sample, 2);
}


short
dsd_input_filter(short sample, int mode)
{
  float sum; int i;
  float gain;
  int zeros;
  float *v, *coeffs;
  switch(mode) {
    case 1:
      gain = ngain;
      v = xv;
      coeffs = xcoeffs;
      zeros = NZEROS;
      break;
    case 2:
      gain = nxgain;
      v = nxv;
      coeffs = nxcoeffs;
      zeros = NXZEROS;
      break;
    default:
      return sample;
  }
  
  for (i = 0; i < zeros; i++)
      v[i] = v[i+1];

  v[zeros] = sample; // unfiltered sample in
  sum = 0.0f;

  for (i = 0; i <= zeros; i++)
    sum += (coeffs[i] * v[i]);

  return sum / ngain; // filtered sample out
}