d_gain2p.c

关于AMR-WB+语音压缩编码的实现代码

/*-------------------------------------------------------------------*
 * procedure d_gain2_plus                                            *
 * ~~~~~~~~~~~~~~~~~~~~~~                                            *
 * Decoding of pitch and codebook gains  (see q_gain2_plus.c)        *
 *-------------------------------------------------------------------*
 * input arguments:                                                  *
 *                                                                   *
 *   indice     :Quantization index                                  *
 *   code[]     :Innovative code vector                              *
 *   lcode      :Subframe size                                       *
 *   bfi        :Bad frame indicator                                 *
 *                                                                   *
 * output arguments:                                                 *
 *                                                                   *
 *   gain_pit   :Quantized pitch gain                                *
 *   gain_code  :Quantized codeebook gain                            *
 *                                                                   *
 * Global variables defining quantizer (in qua_gns.h)                *
 *                                                                   *
 *   t_qua_gain[]    :Table of gain quantizers                       *
 *   nb_qua_gain     :Nombre de quantization levels                  *
 *                                                                   *
 *-------------------------------------------------------------------*/
#include <math.h>
#include <float.h>
#include <stdlib.h>
#include "../include/amr_plus.h"
float d_gain2_plus( /* (o)  : 'correction factor' */
  int index,        /* (i)  : index of quantizer                      */
  float code[],     /* (i)  : Innovative code vector                  */
  int lcode,        /* (i)  : Subframe size                           */
  float *gain_pit,  /* (o)  : Quantized pitch gain                    */
  float *gain_code, /* (o)  : Quantized codebook gain                 */
  int bfi,          /* (i)  : Bad frame indicato                      */
  float mean_ener,  /* (i)  : mean_ener defined in open-loop (2 bits) */
  float *past_gpit, /* (i)  : past gain of pitch                      */
  float *past_gcode)/* (i/o): past gain of code                       */
{
  int   i;
  float ener_code, gcode0;
  const float *t_qua_gain;
  float ener_inov, gcode_inov;
  t_qua_gain = E_ROM_qua_gain7b;
  ener_inov = 0.01f;
  for(i=0; i<lcode; i++) {
    ener_inov += code[i] * code[i];
  }
  gcode_inov = (float)(1.0 / sqrt(ener_inov / (float)lcode));
  /*----------------- Test erasure ---------------*/
  if (bfi != 0)
  {
    if (*past_gpit > 0.95f) {
     *past_gpit = 0.95f;
    }
    if (*past_gpit < 0.5f) {
      *past_gpit = 0.5f;
    }
    *gain_pit = *past_gpit;
    *past_gpit *= 0.95f;
    *past_gcode *= (1.4f - *past_gpit);
    *gain_code = *past_gcode * gcode_inov;
    return *past_gcode;
  }
  /*-------------- Decode gains ---------------*/
  /* innovation energy (without gain) */
  ener_code = 0.01F;
  for(i=0; i<lcode; i++) {
    ener_code += code[i] * code[i];
  }
  ener_code = (float)(10.0 * log10(ener_code /(float)lcode));
  /* predicted codebook gain */
  /* mean energy quantized with 2 bits : 18, 30, 42 or 54 dB */
  gcode0 = mean_ener - ener_code;						
  gcode0 = (float)pow(10.0,gcode0/20.0);   /* predicted gain */
  *gain_pit = t_qua_gain[index*2];
  *gain_code = t_qua_gain[index*2+1] * gcode0;
  /* update bad frame handler */
  *past_gpit = *gain_pit;
  *past_gcode = *gain_code/gcode_inov;
  return t_qua_gain[index*2+1];
}