FreeCalypso > hg > gsm-codec-lib
view libtwamr/dec_lag3.h @ 581:e2d5cad04cbf
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 | fb001496ca8c |
| 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 : dec_lag3.h * Purpose : Decoding of fractional pitch lag with 1/3 resolution. * Extract the integer and fraction parts of the pitch lag from * the received adaptive codebook index. * ******************************************************************************** */ #ifndef dec_lag3_h #define dec_lag3_h "$Id $" /* ******************************************************************************** * INCLUDE FILES ******************************************************************************** */ #include "typedef.h" /* ******************************************************************************** * LOCAL VARIABLES AND TABLES ******************************************************************************** */ /* ******************************************************************************** * DEFINITION OF DATA TYPES ******************************************************************************** */ /* ******************************************************************************** * DECLARATION OF PROTOTYPES ******************************************************************************** */ /************************************************************************* * FUNCTION: Dec_lag3 * * PURPOSE: Decoding of fractional pitch lag with 1/3 resolution. * Extract the integer and fraction parts of the pitch lag from * the received adaptive codebook index. * * See "Enc_lag3.c" for more details about the encoding procedure. * * The fractional lag in 1st and 3rd subframes is encoded with 8 bits * while that in 2nd and 4th subframes is relatively encoded with 4, 5 * and 6 bits depending on the mode. * *************************************************************************/ void Dec_lag3(Word16 index, /* i : received pitch index */ Word16 T0_min, /* i : minimum of search range */ Word16 T0_max, /* i : maximum of search range */ Word16 i_subfr, /* i : subframe flag */ Word16 T0_prev, /* i : integer pitch delay of last subframe used in 2nd and 4th subframes */ Word16 * T0, /* o : integer part of pitch lag */ Word16 * T0_frac, /* o : fractional part of pitch lag */ Word16 flag4 /* i : flag for encoding with 4 bits */ ); #endif