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view libtwamr/b_cn_cod.h @ 581:e2d5cad04cbf

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libgsmhr1 RxFE: store CN R0+LPC separately from speech In the original GSM 06.06 code the ECU for speech mode is entirely separate from the CN generator, maintaining separate state. (The main intertie between them is the speech vs CN state variable, distinguishing between speech and CN BFIs, in addition to the CN-specific function of distinguishing between initial and update SIDs.) In the present RxFE implementation I initially thought that we could use the same saved_frame buffer for both ECU and CN, overwriting just the first 4 params (R0 and LPC) when a valid SID comes in. However, I now realize it was a bad idea: the original code has a corner case (long sequence of speech-mode BFIs to put the ECU in state 6, then SID and CN-mode BFIs, then a good speech frame) that would be broken by that buffer reuse approach. We could eliminate this corner case by resetting the ECU state when passing through a CN insertion period, but doing so would needlessly increase the behavioral diffs between GSM 06.06 and our version. Solution: use a separate CN-specific buffer for CN R0+LPC parameters, and match the behavior of GSM 06.06 code in this regard.
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 13 Feb 2025 10:02:45 +0000
parents 07f936338de1
children
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/*
********************************************************************************
*
*      GSM AMR-NB speech codec   R98   Version 7.6.0   December 12, 2001
*                                R99   Version 3.3.0                
*                                REL-4 Version 4.1.0                
*
********************************************************************************
*
*      File             : b_cn_cod.h
*      Purpose          : Contains function for comfort noise generation.
*
********************************************************************************
*/
#ifndef b_cn_cod_h
#define b_cn_cod_h "$Id $"

/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"

/*
********************************************************************************
*                         DEFINITION OF DATA TYPES
********************************************************************************
*/

/*
********************************************************************************
*                         DECLARATION OF PROTOTYPES
********************************************************************************
*/

/*************************************************************************
 *
 *   FUNCTION NAME: pseudonoise
 *
 *   PURPOSE: Generate a random integer value to use in comfort noise
 *            generation. The algorithm uses polynomial x^31 + x^3 + 1
 *            (length of PN sequence is 2^31 - 1).
 *
 *   INPUTS:      *shift_reg    Old CN generator shift register state
 *
 *
 *   OUTPUTS:     *shift_reg    Updated CN generator shift register state
 *
 *   RETURN VALUE: Generated random integer value
 *
 *************************************************************************/

Word16 pseudonoise (
    Word32 *shift_reg, /* i/o : Old CN generator shift register state */
    Word16 no_bits     /* i   : Number of bits                        */
);

/*************************************************************************
 *
 *   FUNCTION NAME: build_CN_code
 *
 *   PURPOSE: Compute the comfort noise fixed codebook excitation. The
 *            gains of the pulses are always +/-1.
 *
 *   INPUTS:      *seed         Old CN generator shift register state
 *
 *   OUTPUTS:     cod[0..39]    Generated comfort noise fixed codebook vector
 *                *seed         Updated CN generator shift register state
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/
void build_CN_code (
    Word32 *seed,         /* i/o : Old CN generator shift register state */
    Word16 cod[]          /* o   : Generated CN fixed codebook vector    */
);

/*************************************************************************
 *
 *   FUNCTION NAME: build_CN_param
 *
 *   PURPOSE: Randomize the speech parameters. So that they 
 *            do not produce tonal artifacts if used by ECU.
 *
 *   INPUTS:      *seed            Old CN generator shift register state
 *                n_param,         Number of parameters to randomize
 *                parm_size_table, 
 *                  
 *
 *   OUTPUTS:      parm    CN Generated Parameters
 *                *seed    Updated CN generator shift register state
 *
 *   RETURN VALUE: none
 *
 *************************************************************************/
void build_CN_param (
    Word16 *seed,              /* i/o : Old CN generator shift register state */
    const Word16 n_param,            /* i : number of params     */  
    const Word16 param_size_table[], /* i : size of params       */   
    Word16 parm[]              /* o   : CN Generated Params*/
);

#endif