isp_isf.c

关于AMR-WB+语音压缩编码的实现代码

/*-----------------------------------------------------------------------*
 *   Functions : isp2isf and isf2isp                                     *
 *                                                                       *
 *      isp2isf   Transformation isp to isf                              *
 *      isf2isp   Transformation isf to isp                              *
 *                                                                       *
 *   ISP are immitance spectral pair in cosine domain (-1 to 1).         *
 *   ISF are immitance spectral pair in frequency domain (0 to 6400).    *
 *-----------------------------------------------------------------------*/
#include <math.h>
#include <float.h>
#include "../include/amr_plus.h"
#define SCALE1  (6400.0/PI)
#define SCALE2  (PI/6400.0)
#ifndef PI
#define PI      3.141592654
#endif
void isf2isp(
  float isf[],    /* input : isf[m] normalized (range: 0<=val<=6400)  */
  float isp[],    /* output: isp[m] (range: -1<=val<1)                */
  int   m         /* input : LPC order                                */
)
{
  int i;
  /*  convert ISFs to the cosine domain */
  for(i=0; i<m-1; i++) {
    isp[i] = (float)cos(isf[i] * SCALE2);
  }
  isp[m-1] = (float)cos(isf[m-1] * SCALE2 * 2.0);
  return;
}