phi_prep.c

语音压缩算法

/*====================================================================*/
/*         MPEG-4 Audio (ISO/IEC 14496-3) Copyright Header            */
/*====================================================================*/
/*
This software module was originally developed by Rakesh Taori and Andy
Gerrits (Philips Research Laboratories, Eindhoven, The Netherlands) in
the course of development of the MPEG-4 Audio (ISO/IEC 14496-3). This
software module is an implementation of a part of one or more MPEG-4
Audio (ISO/IEC 14496-3) tools as specified by the MPEG-4 Audio
(ISO/IEC 14496-3). ISO/IEC gives users of the MPEG-4 Audio (ISO/IEC
14496-3) free license to this software module or modifications thereof
for use in hardware or software products claiming conformance to the
MPEG-4 Audio (ISO/IEC 14496-3). Those intending to use this software
module in hardware or software products are advised that its use may
infringe existing patents. The original developer of this software
module and his/her company, the subsequent editors and their
companies, and ISO/IEC have no liability for use of this software
module or modifications thereof in an implementation. Copyright is not
released for non MPEG-4 Audio (ISO/IEC 14496-3) conforming products.
CN1 retains full right to use the code for his/her own purpose, assign
or donate the code to a third party and to inhibit third parties from
using the code for non MPEG-4 Audio (ISO/IEC 14496-3) conforming
products.  This copyright notice must be included in all copies or
derivative works. Copyright 1996.
*/
/*====================================================================*/
/*======================================================================*/
/*                                                                      */
/*      SOURCE_FILE:    PHI_PREP.C                                      */
/*      PACKAGE:        WDBxx                                           */
/*      COMPONENT:      Preprocessing Module                            */
/*                                                                      */
/*======================================================================*/

/*======================================================================*/
/*      I N C L U D E S                                                 */
/*======================================================================*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "phi_prep.h"

/*======================================================================*/
/* Function Definition: celp_preprocessing                              */
/*======================================================================*/
void                            /* Return Value: Void                   */
celp_preprocessing
(
float InputSignal[],            /* In:  Input Signal                    */
float PP_InputSignal[],         /* Out: Preprocessed Input Signal       */   
float *prev_x,                  /* In/Out: Previous x                   */
float *prev_y,                  /* In/Out: Previous y                   */
long  frame_size,               /* In:  Number of samples in frame      */
long  sampling_frequency        /* In:  Sampling Frequency              */
)
{

    /* -----------------------------------------------------------------*/
    /*Volatile Variables                                                */
    /* -----------------------------------------------------------------*/
    register float *in_ptr  = InputSignal;
    register float *out_ptr = PP_InputSignal;
    register float mult_fac = (float)0.990000000;
    register int   n        = (int)frame_size;
    
    /* -----------------------------------------------------------------*/
    /* Perform DC filtering                                             */
    /* -----------------------------------------------------------------*/
    do
    {   
        *out_ptr = *in_ptr - *prev_x + (*prev_y * mult_fac);
        *prev_y    = *out_ptr++;
        *prev_x    = *in_ptr++;
    }
    while(--n);
    
    /* -----------------------------------------------------------------*/
    /*Since a string of zeros can create a very low value; it is safe to*/ 
    /*set prevy to zero once it gets really small                       */
    /* -----------------------------------------------------------------*/
    if (fabs((double)*prev_y) < 1e-17)
    {    
        *prev_y = (float)0.0;
    }
}

/*======================================================================*/
/*      H I S T O R Y                                                   */
/*======================================================================*/
/* 17-04-96 R. Taori  Initial Version                                   */
/* 30-07-96 R. Taori  Modified interface  to meet the MPEG-4 requirement*/