?? mdefir2.c
字號:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "msp.h"
void mdefir2(int l,int iband,float fl,float fh,complex b[],
float trans,float fs,int *ierror)
{
/*---------------------------------------------------------------------
Fl:low cut-off frequency. Fh:high cut-off(For BP,BS). fl,fh,fs in Hz
|--- | --- | --- |-- --
| | | | | | | | | |
| | | | | | | | | |
--|------ -|-------- -|----------- --|--------------
0 fl 0 fl 0 fl fh 0 fl fh
Digital filter coefficients are returned in b(l)
h(z)=b(0)+b(1)z^(-1)+ ... +b(l-1)z^(-l+1)
Input parameters:
l : the length of FIR filter. l<201 and l must be the odd.
iband: iband=1 low pass FIR filter.
iband=2 high pass FIR filter.
iband=3 band pass FIR filter.
iband=4 band stop FIR filter.
trans: 0<= trans <1.0 , it is the transition point.
Output parameters:
b: l dimensioned real array.the result is in b(0) to b(l-1).
in Chapter 8
---------------------------------------------------------------------*/
complex h[201];
complex z;
int i,lim,nlow,nhigh;
float pi,fln,fhn,dly,band,s;
pi=4.*atan(1.);
fln=fl/fs;
fhn=fh/fs;
for(i=0;i<l;i++)
{h[i].real=0.;
h[i].imag=0.0;
}
*ierror=0;
dly=(float)l/2.;
lim=l/2;
if(dly==(float)lim)
*ierror=1;
if(l>=201)
*ierror=2;
if(iband==4)
band=(fhn-fln)*l;
if(iband==4&&band<4.)
{
printf(" Please increse the length L for Band-Stop Filter\n");
*ierror=3;
}
if(iband<1||iband>4)
*ierror=4;
if(fln<=0.||fln>0.5)
*ierror=5;
if(iband>=3&&fln>=fhn)
*ierror=6;
if(trans<0.0&&trans>=1.)
*ierror=7;
if(*ierror!=0)
return;
s=-(l-1)*pi/l;
switch(iband)
{case 1:
{
nlow=1;
nhigh=fln*l-1;
h[0].real=1.0;h[0].imag=0.0;
for(i=nlow;i<=nhigh;i++)
{
z.real=0.0;
z.imag=s*i;
z=cexp(z);
h[i].real=z.real;
h[i].imag=z.imag;
h[l-i].real=h[i].real;
h[l-i].imag=-h[i].imag;
}
z.real=0.0;
z.imag=s*(nhigh+1);
z=cexp(z);
h[nhigh+1].real=trans*z.real;
h[nhigh+1].imag=trans*z.imag;
h[l-nhigh-1].real=h[nhigh+1].real;
h[l-nhigh-1].imag=-h[nhigh+1].imag;
break;
}
case 2:
{
h[0].real=0.0;
h[0].imag=0.0;
nlow=fln*l;
nhigh=lim;
for(i=nlow;i<=nhigh;i++)
{z.real=0.0;
z.imag=s*i;
z=cexp(z);
h[i].real=z.real;
h[i].imag=z.imag;
h[l-i].real=h[i].real;
h[l-i].imag=-h[i].imag;
}
z.real=0.0;
z.imag=s*(nlow-1);
z=cexp(z);
h[nlow-1].real=trans*z.real;
h[nlow-1].imag=trans*z.imag;
h[l-nlow+1].real=h[nlow-1].real;
h[l-nlow+1].imag=-h[nlow-1].imag;
break;
}
case 3:
{
nlow=fln*l;
nhigh=fhn*l;
h[0].real=0.0;h[0].imag=0.0;
for(i=nlow;i<=nhigh;i++)
{z.real=0.0;z.imag=s*i;
z=cexp(z);
h[i].real=z.real;
h[i].imag=z.imag;
h[l-i].real=h[i].real;
h[l-i].imag=-h[i].imag;
}
z.real=0.0;
z.imag=s*(nhigh+1);
z=cexp(z);
h[nhigh+1].real=trans*z.real;
h[nhigh+1].imag=trans*z.imag;
h[l-nhigh-1].real=h[nhigh+1].real;
h[l-nhigh-1].imag=-h[nhigh+1].imag;
z.real=0.0;
z.imag=s*(nlow-1);
z=cexp(z);
h[nlow-1].real=trans*z.real;
h[nlow-1].imag=trans*z.imag;
h[l-nlow+1].real=h[nlow-1].real;
h[l-nlow+1].imag=-h[nlow-1].imag;
break;
}
case 4:
{
nlow=1;
nhigh=fln*l-1;
h[0].real=1.0;h[0].imag=0.0;
for(i=nlow;i<=nhigh;i++)
{z.real=0.0;
z.imag=s*i;
z=cexp(z);
h[i].real=z.real;
h[i].imag=z.imag;
h[l-i].real=h[i].real;
h[l-i].imag=-h[i].imag;
}
z.real=0.0;
z.imag=s*(nhigh+1);
z=cexp(z);
h[nhigh+1].real=trans*z.real;
h[nhigh+1].imag=trans*z.imag;
h[l-nhigh-1].real=h[nhigh+1].real;
h[l-nhigh-1].imag=-h[nhigh+1].imag;
nlow=fhn*l;
nhigh=lim;
for(i=nlow;i<=nhigh;i++)
{z.real=0.0;
z.imag=s*i;
z=cexp(z);
h[i].real=z.real;
h[i].imag=z.imag;
h[l-i].real=h[i].real;
h[l-i].imag=-h[i].imag;
}
z.real=0.0;
z.imag=s*(nlow-1);
z=cexp(z);
h[nlow-1].real=trans*z.real;
h[nlow-1].imag=trans*z.imag;
h[l-nlow+1].real=h[nlow-1].real;
h[l-nlow+1].imag=-h[nlow-1].imag;
break;
}
}
mcmpdft(h,b,l,1);
}
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