www.pudn.com > AVS_M_ver10.rar > hp50.c

/* 
*********************************************************************** 
* COPYRIGHT AND WARRANTY INFORMATION 
* 
* Copyright 2007  Audio Video Coding Standard, Part ¢ú 
* 
* This software module was developed by AVS Audio sub-group 
* 
* DISCLAIMER OF WARRANTY 
* 
* These software programs are available to the users without any 
* license fee or royalty on an "as is" basis. The AVS disclaims 
* any and all warranties, whether express, implied, or statutory, 
* including any implied warranties of merchantability or of fitness 
* for a particular purpose. In no event shall the contributors or  
* the AVS be liable for any incidental, punitive, or consequential 
* damages of any kind whatsoever arising from the use of this program. 
* 
* This disclaimer of warranty extends to the user of this program 
* and user's customers, employees, agents, transferees, successors, 
* and assigns. 
* 
* The AVS does not represent or warrant that the program furnished 
* hereunder are free of infringement of any third-party patents. 
* Commercial implementations of AVS, including shareware, may be 
* subject to royalty fees to patent holders. Information regarding 
* the AVS patent policy is available from the AVS Web site at 
* http://www.avs.org.cn 
* 
* THIS IS NOT A GRANT OF PATENT RIGHTS - SEE THE AVS PATENT POLICY. 
************************************************************************ 
*/ 
 
#include "../include/amr_plus.h" 
/* 
 * hp50_12k8 
 * 
 * Function: 
 *    2nd order high pass filter with nominal cut off frequency at 50 Hz. 
 * 
 * Returns: 
 *    void 
 */ 
void hp50_12k8(Float32 signal[], Word32 lg, Float32 mem[], Word32 fscale) 
{ 
   Word16 i; 
   Float32 x0, x1, x2, y0, y1, y2; 
   Float32 a1, a2, b1, b2, frac; 
   y1 = mem[0]; 
   y2 = mem[1]; 
   x0 = mem[2]; 
   x1 = mem[3]; 
   if (fscale >= FSCALE_DENOM) 
   { 
      /* design in matlab (-3dB @ 20 Hz) 
         [b,a] = butter(2, 20.0/6400.0, 'high'); 
         a = [1.00000000000000  -1.98611621154089   0.98621192916075]; 
         b = [0.99308203517541  -1.98616407035082   0.99308203517541]; 
         [b,a] = butter(2, 20.0/12800.0, 'high'); 
         a = [1.00000000000000  -1.99305802314321   0.99308203546221]; 
         b = [0.99653501465135  -1.99307002930271   0.99653501465135]; 
         difference: 
         a = [               0  -0.00694181160232   0.00687010630146]; 
         b = [0.00345297947594  -0.00690595895189   0.00345297947594]; 
      */ 
      /* this approximation is enough (max overshoot = +0.05dB) */ 
      frac = ((Float32)(fscale-FSCALE_DENOM)) / ((Float32)FSCALE_DENOM); 
      a1 =  1.98611621154089f + (frac*0.00694181160232f); 
      a2 = -0.98621192916075f - (frac*0.00687010630146f); 
      b1 = -1.98616407035082f - (frac*0.00690595895189f); 
      b2 =  0.99308203517541f + (frac*0.00345297947594f); 
      for(i = 0; i < lg; i++) 
      { 
         x2 = x1; 
         x1 = x0; 
         x0 = signal[i]; 
         y0 = (y1*a1) + (y2*a2) + (x0*b2) + (x1*b1) + (x2*b2); 
         signal[i] = y0; 
         y2 = y1;                                                               
         y1 = y0; 
      } 
   } 
   else           /* -6dB 24Hz fs/2=6400Hz (3GPP AMR-WB coef) */ 
   { 
      for(i = 0; i < lg; i++) 
      { 
         x2 = x1; 
         x1 = x0; 
         x0 = signal[i]; 
         y0 = y1 * 1.978881836F + y2 * -0.979125977F + x0 * 0.989501953F + 
            x1 * -1.979003906F + x2 * 0.989501953F; 
         signal[i] = y0; 
         y2 = y1;                                                               
         y1 = y0; 
      } 
   } 
   mem[0] = ((y1 > 1e-10) | (y1 < -1e-10)) ? y1 : 0; 
   mem[1] = ((y2 > 1e-10) | (y2 < -1e-10)) ? y2 : 0; 
   mem[2] = ((x0 > 1e-10) | (x0 < -1e-10)) ? x0 : 0; 
   mem[3] = ((x1 > 1e-10) | (x1 < -1e-10)) ? x1 : 0; 
   return; 
}