int_lpc.c

关于AMR-WB+语音压缩编码的实现代码

/*---------------------------------------------------------------------*
 * routine int_lpc()                                                   *
 * ~~~~~~~~~~~~~~~~~                                                   *
 * Find the interpolated LPC parameters in every subframes.            *
 *---------------------------------------------------------------------*/
#include "../include/amr_plus.h"
void int_lpc_np1(
  float isf_old[],  /* input : LSFs from past frame              */
  float isf_new[],  /* input : LSFs from present frame           */
  float a[],        /* output: LP coefficients in both subframes */
  int   nb_subfr,   /* input: number of subframe                 */
  int   m           /* input : order of LP filter                */
)
{
  float isf[M], inc, fnew, fold, *p_a;
  int i, k;
  inc = 1.0f / (float)nb_subfr;
  p_a = a;
  fnew = 0.0f;
  for (k=0; k<nb_subfr; k++)
  {
    fold = 1.0f - fnew;
    for (i = 0; i < m; i++) {
      isf[i] = isf_old[i]*fold + isf_new[i]*fnew;
    }
    fnew += inc;
    E_LPC_f_isp_a_conversion(isf, p_a, m);
    p_a += (m+1);
  }  
  /* estimated coef for next subframe: use isf_new */
  E_LPC_f_isp_a_conversion(isf_new, p_a, m);
  return;
}