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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 38ee82480462
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             : pre_big.h
*      Purpose          : Big subframe (2 subframes) preprocessing
*
********************************************************************************
*/
#ifndef pre_big_h
#define pre_big_h "$Id $"

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

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

int pre_big(
    enum Mode mode,            /* i  : coder mode                             */
    const Word16 gamma1[],     /* i  : spectral exp. factor 1                 */
    const Word16 gamma1_12k2[],/* i  : spectral exp. factor 1 for EFR         */
    const Word16 gamma2[],     /* i  : spectral exp. factor 2                 */
    Word16 A_t[],              /* i  : A(z) unquantized, for 4 subframes, Q12 */
    Word16 frameOffset,        /* i  : Start position in speech vector,   Q0  */
    Word16 speech[],           /* i  : speech,                            Q0  */
    Word16 mem_w[],            /* i/o: synthesis filter memory state,     Q0  */
    Word16 wsp[]               /* o  : weighted speech                    Q0  */
);

#endif