FreeCalypso > hg > gsm-codec-lib
view libtwamr/az_lsp.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 | 54f6bc41ed10 |
| children |
line wrap: on
line source
/* ******************************************************************************** * * 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 : az_lsp.h * ******************************************************************************** */ #ifndef az_lsp_h #define az_lsp_h "$Id $" /* ******************************************************************************** * INCLUDE FILES ******************************************************************************** */ #include "typedef.h" /* ******************************************************************************** * DEFINITION OF DATA TYPES ******************************************************************************** */ /* ******************************************************************************** * DECLARATION OF PROTOTYPES ******************************************************************************** */ /* ************************************************************************** * * Function : Az_lsp * Purpose : Compute the LSPs from the LP coefficients * Description : - The sum and difference filters are computed * and divided by 1+z^{-1} and 1-z^{-1}, respectively. * * f1[i] = a[i] + a[11-i] - f1[i-1] ; i=1,...,5 * f2[i] = a[i] - a[11-i] + f2[i-1] ; i=1,...,5 * * - The roots of F1(z) and F2(z) are found using * Chebyshev polynomial evaluation. The polynomials * are evaluated at 60 points regularly spaced in the * frequency domain. The sign change interval is * subdivided 4 times to better track the root. The * LSPs are found in the cosine domain [1,-1]. * * - If less than 10 roots are found, the LSPs from * the past frame are used. * Returns : void * ************************************************************************** */ void Az_lsp ( Word16 a[], /* (i) : predictor coefficients (MP1) */ Word16 lsp[], /* (o) : line spectral pairs (M) */ Word16 old_lsp[] /* (i) : old lsp[] (in case not found 10 roots) (M)*/ ); #endif