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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 a0f914a28371
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             : post_pro.h
*      Purpose          : Postprocessing of output speech.
*
*                         - 2nd order high pass filtering with cut
*                           off frequency at 60 Hz.
*                         - Multiplication of output by two.
*
********************************************************************************
*/
#ifndef post_pro_h
#define post_pro_h "$Id $"
 
/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"
 
/*
********************************************************************************
*                         LOCAL VARIABLES AND TABLES
********************************************************************************
*/
 
/*
********************************************************************************
*                         DEFINITION OF DATA TYPES
********************************************************************************
*/
typedef struct {
   Word16 y2_hi;
   Word16 y2_lo;
   Word16 y1_hi;
   Word16 y1_lo;
   Word16 x0;
   Word16 x1;
} Post_ProcessState;
 
/*
********************************************************************************
*                         DECLARATION OF PROTOTYPES
********************************************************************************
*/
 
void Post_Process_reset (Post_ProcessState *st);
/* reset of Post processing state (i.e. set state memory to zero)
   returns 0 on success
 */

int Post_Process (
    Post_ProcessState *st,  /* i/o : post process state                   */
    Word16 signal[],        /* i/o : signal                               */
    Word16 lg               /* i   : lenght of signal                     */
    );

#endif