#include <stdio.h>
const  int length = 180 /*語音幀長為180點＝22.5ms@8kHz采樣*/
void  filter(int xin[ ],int xout[ ],int n,float h[ ]); /*濾波子程序說明*/
/*19點濾波器系數(shù)*/
static  float h[19]=
    {0.01218354,-0.009012882,-0.02881839,-0.04743239,-0.04584568,
-0.008692503,0.06446265,0.1544655,0.2289794,0.257883,
0.2289794,0.1544655,0.06446265,-0.008692503,-0.04584568,
-0.04743239,-0.02881839,-0.009012882,0.01218354};
static  int x1[length+20];
/*低通濾波浮點子程序*/
void  filter(int xin[ ],int xout[ ],int n,float h[ ])
{
    int i,j;
    float sum;
    for(i=0;i<length;i++) x1[n+i-1]=xin[i];
    for (i=0;i<length;i++)
    {
        sum=0.0;
        for(j=0;j<n;j++) sum+=h[j]*x1[i-j+n-1];
        xout[i]=(int)sum;
    }
    for(i=0;i<(n-1);i++) x1[n-i-2]=xin[length-1-i];
}
 
/*主程序*/
void  main( )
{
    FILE    *fp1,*fp2;
    int     frame,indata[length],outdata[length];
    fp1=fopen(insp.dat,"rb");              /*輸入語音文件*/
    fp2=fopen(outsp.dat,"wb");           /*濾波后語音文件*/
 
    frame=0;
    while(feof(fp1)==0)
    {
        frame++;
        printf("frame=%d/n",frame);
        for(i=0;i<length;i++)  indata[i]=getw(fp1);        /*取一幀語音數(shù)據(jù)*/
        filter(indata,outdata,19,h);            /*調(diào)用低通濾波子程序*/
        for(i=0;i<length;i++)  putw(outdata[i],fp2);     /*將濾波后的樣值寫入文件*/
    }
    fcloseall( );                   /*關(guān)閉文件*/
    return(0);
}

#include <stdio.h>
const int length=180;
void  filter(int xin[ ],int xout[ ],int n,int h[ ]);
static int  h[19]={399,-296,-945,-1555,-1503,-285,2112,5061,7503,8450,
    7503,5061,2112,-285,-1503,-1555,-945,-296,399};           /*Q15*/
static int  x1[length+20];
/*低通濾波定點子程序*/
void  filter(int xin[ ],int xout[ ],int n,int h[ ])
{
    int i,j;
    long sum;
    for(i=0;i<length;i++) x1[n+i-1]=xin[i];
    for (i=0;i<length;i++)
    {
        sum=0;
        for(j=0;j<n;j++)  sum+=(long)h[j]*x1[i-j+n-1];
        xout[i]=sum>>15;
    }
    for(i=0;i<(n-1);i++) x1[n-i-2]=xin[length-i-1];
}