int makeFilter(HWORD Imp[], HWORD ImpD[], UHWORD *LpScl, UHWORD Nwing,
double Froll, double Beta)
{
double DCgain, Scl, Maxh;
HWORD Dh;
int i, temp;
if (Nwing > MAXNWING) /* Check for valid parameters */
return(1);
if ((Froll<=0) || (Froll>1))
return(2);
if (Beta < 1)
return(3);
/*
* Design Kaiser-windowed sinc-function low-pass filter
*/
LpFilter(ImpR, (int)Nwing, 0.5*Froll, Beta, Npc);
/* Compute the DC gain of the lowpass filter, and its maximum coefficient
* magnitude. Scale the coefficients so that the maximum coeffiecient just
* fits in Nh-bit fixed-point, and compute LpScl as the NLpScl-bit (signed)
* scale factor which when multiplied by the output of the lowpass filter
* gives unity gain. */
DCgain = 0;
Dh = Npc; /* Filter sampling period for factors>=1 */
for (i=Dh; i<Nwing; i+=Dh)
DCgain += ImpR[i];
DCgain = 2*DCgain + ImpR[0]; /* DC gain of real coefficients */
for (Maxh=i=0; i<Nwing; i++)
Maxh = MAX(Maxh, fabs(ImpR[i]));
Scl = ((1<<(Nh-1))-1)/Maxh; /* Map largest coeff to 16-bit maximum */
temp = (int) fabs((1<<(NLpScl+Nh))/(DCgain*Scl));
if (temp >= 1<<16)
return(4); /* Filter scale factor overflows UHWORD */
*LpScl = temp;
/* Scale filter coefficients for Nh bits and convert to integer */
if (ImpR[0] < 0) /* Need pos 1st value for LpScl storage */
Scl = -Scl;
for (i=0; i<Nwing; i++) /* Scale them */
ImpR[i] *= Scl;
for (i=0; i<Nwing; i++) /* Round them */
Imp[i] = (int) (ImpR[i] + 0.5);
/* ImpD makes linear interpolation of the filter coefficients faster */
for (i=0; i<Nwing-1; i++)
ImpD[i] = Imp[i+1] - Imp[i];
ImpD[Nwing-1] = - Imp[Nwing-1]; /* Last coeff. not interpolated */
return(0);
}
int makeFilter(Float Imp[], long Nwing, double Froll, double Beta,
long Num, int Normalize)
{
double *ImpR;
long Mwing, i;
if (Nwing > MAXNWING) /* Check for valid parameters */
return(-1);
if ((Froll<=0) || (Froll>1))
return(-2);
/* it does help accuracy a bit to have the window stop at
* a zero-crossing of the sinc function */
Mwing = (long)floor((double)Nwing/(((double)Num)/Froll))*(((double)Num)/Froll) +0.5;
if (Mwing==0)
return(-4);
ImpR = (double *) malloc(sizeof(double) * Mwing);
/* Design a Nuttall or Kaiser windowed Sinc low-pass filter */
LpFilter(ImpR, Mwing, Froll, Beta, Num);
if (Normalize) { /* 'correct' the DC gain of the lowpass filter */
long Dh;
double DCgain;
DCgain = 0;
Dh = Num; /* Filter sampling period for factors>=1 */
for (i=Dh; i<Mwing; i+=Dh)
DCgain += ImpR[i];
DCgain = 2*DCgain + ImpR[0]; /* DC gain of real coefficients */
/*st_report("DCgain err=%.12f",DCgain-1.0);*/
DCgain = 1.0/DCgain;
for (i=0; i<Mwing; i++)
Imp[i] = ImpR[i]*DCgain;
} else {
for (i=0; i<Mwing; i++)
Imp[i] = ImpR[i];
}
free(ImpR);
for (i=Mwing; i<=Nwing; i++) Imp[i] = 0;
/* Imp[Mwing] and Imp[-1] needed for quadratic interpolation */
Imp[-1] = Imp[1];
return(Mwing);
}
