ptcode.c

语音CELP压缩解压源代码（C语音)

/**************************************************************************
*
* ROUTINE
*		pitchencode
*
* FUNCTION
*
*		encode and quantize pitch gain (bb(3)) for various
*		quantizer types.
*
* SYNOPSIS
*		subroutine pitchencode(input, index)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*	input		int	i	pitch gain input (true value)
*	index		float	o	encoded pitch gain index
*	pitchencode	float	fun	encoded pitch gain
*
***************************************************************************
*
* DESCRIPTION
*
*	This funtion uses output level data obtained by Max's minimum
*	distortion quantization priciples and quantizes to the nearest
*	level (L1 norm).  (Using level data only was found superior to
*	using both of Max's level and boundry data.)
*
***************************************************************************
*
* CALLED BY
*
*	psearch
*
* CALLS
*
*	
***************************************************************************
*
* REFERENCES
*
*	Quantizing for Minimum Distorion
*	J. Max
*	IRE Trans. Inform. Theory, vol. IT-6, pp.7-12, Mar. 1960
*
***************************************************************************
*
*	The data used in the table generation is from 3m3f.spd.
*
**************************************************************************/
#include <math.h>
static float pitch2max5[32] =
{
  -0.993, -0.831, -0.693, -0.555, -0.414, -0.229,    0.0,  0.139,
   0.255,  0.368,  0.457,  0.531,  0.601,  0.653,  0.702,  0.745,
   0.780,  0.816,  0.850,  0.881,  0.915,  0.948,  0.983,  1.020, 
   1.062,  1.117,  1.193,  1.289,  1.394,  1.540,  1.765,  1.991
};

float
pitchencode(input, index)
int *index;
float input;

{
  int i;
  float dist, low;
  
  low = dist = fabs(input - *pitch2max5);
  *index = 0;
  for (i = 1; i < 32; i++)
  {
    dist = fabs(input - pitch2max5[i]);
    if (dist < low)
    {
      low = dist;
      *index = i;
    }
  }
  return (pitch2max5[*index]);
}
/**************************************************************************
*
* ROUTINE
*		pitchdecode
*
* FUNCTION
*
*		decode pitch gain (bb(3)) from pitch index and bit
*		index (bits)
*
* SYNOPSIS
*		subroutine pitchdecode(pindex, pitch)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*	pindex		int	i	pitch index value
*	pitch		float	o	pitch gain decoded
*
***************************************************************************
*
* DESCRIPTION
*
*
***************************************************************************
*
* CALLED BY
*
*	dcodpg
*
* CALLS
*
*
***************************************************************************
*
*	The data used in the table generation is from 3m3f.spd.
*
***************************************************************************
*
* REFERENCES
*
*	Quantizing for Minimum Distorion
*	J. Max
*	IRE Trans. Inform. Theory, vol. IT-6, pp.7-12, Mar. 1960
*
***************************************************************************
*
*	The data used in the table generation is from 3m3f.spd.
*
**************************************************************************/
pitchdecode(pindex, pitch)
int pindex;
float *pitch;

{
  *pitch = pitch2max5[pindex];
}