syntfilter.cxx

MiniSip Client with DomainKeys Authentication, Sip, Audio communications, Echo Cancel

//A.48 syntFilter.c 
    
   /****************************************************************** 
    
       iLBC Speech Coder ANSI-C Source Code 
    
       syntFilter.c  
    
       Copyright (c) 2001, 
       Global IP Sound AB. 
       All rights reserved. 
    
   ******************************************************************/ 
    
   #include"iLBC_define.h" 
    
   /*----------------------------------------------------------------* 
    *  LP synthesis filter. 
    *---------------------------------------------------------------*/ 
        
   void syntFilter( 
       float *Out,     /* (i/o) Signal to be filtered */ 
       float *a,       /* (i) LP parameters */ 
       int len,    /* (i) Length of signal */ 
       float *mem      /* (i/o) Filter state */ 
   ){ 
       int i, j; 
       float *po, *pi, *pa, *pm; 
    
       po=Out; 
    
       /* Filter first part using memory from past */ 
    
       for (i=0;i<LPC_FILTERORDER;i++) { 
           pi=&Out[i-1]; 
           pa=&a[1]; 
           pm=&mem[LPC_FILTERORDER-1]; 
           for (j=1;j<=i;j++) { 
               *po-=(*pa++)*(*pi--); 
           } 
           for (j=i+1;j<LPC_FILTERORDER+1;j++) { 
               *po-=(*pa++)*(*pm--); 
           } 
           po++; 
       } 
    
       /* Filter last part where the state is entierly in  
          the output vector */ 
        
     
       for (i=LPC_FILTERORDER;i<len;i++) { 
           pi=&Out[i-1]; 
           pa=&a[1]; 
           for (j=1;j<LPC_FILTERORDER+1;j++) { 
               *po-=(*pa++)*(*pi--); 
           } 
           po++; 
       } 
    
       /* Update state vector */ 
    
       memcpy(mem, &Out[len-LPC_FILTERORDER],  
           LPC_FILTERORDER*sizeof(float)); 
   }