ref: eb61c31c14107dd4b02e40977b14cbda36ab8b6b
dir: /silk/float/find_LPC_FLP.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "define.h"
#include "main_FLP.h"
#include "tuning_parameters.h"
/* LPC analysis */
void silk_find_LPC_FLP(
silk_encoder_state *psEncC, /* I/O Encoder state */
opus_int16 NLSF_Q15[], /* O NLSFs */
const silk_float x[], /* I Input signal */
const silk_float minInvGain /* I Inverse of max prediction gain */
)
{
opus_int k, subfr_length;
silk_float a[ MAX_LPC_ORDER ];
/* Used only for NLSF interpolation */
silk_float res_nrg, res_nrg_2nd, res_nrg_interp;
opus_int16 NLSF0_Q15[ MAX_LPC_ORDER ];
silk_float a_tmp[ MAX_LPC_ORDER ];
silk_float LPC_res[ MAX_FRAME_LENGTH + MAX_NB_SUBFR * MAX_LPC_ORDER ];
subfr_length = psEncC->subfr_length + psEncC->predictLPCOrder;
/* Default: No interpolation */
psEncC->indices.NLSFInterpCoef_Q2 = 4;
/* Burg AR analysis for the full frame */
res_nrg = silk_burg_modified_FLP( a, x, minInvGain, subfr_length, psEncC->nb_subfr, psEncC->predictLPCOrder );
if( psEncC->useInterpolatedNLSFs && !psEncC->first_frame_after_reset && psEncC->nb_subfr == MAX_NB_SUBFR ) {
/* Optimal solution for last 10 ms; subtract residual energy here, as that's easier than */
/* adding it to the residual energy of the first 10 ms in each iteration of the search below */
res_nrg -= silk_burg_modified_FLP( a_tmp, x + ( MAX_NB_SUBFR / 2 ) * subfr_length, minInvGain, subfr_length, MAX_NB_SUBFR / 2, psEncC->predictLPCOrder );
/* Convert to NLSFs */
silk_A2NLSF_FLP( NLSF_Q15, a_tmp, psEncC->predictLPCOrder );
/* Search over interpolation indices to find the one with lowest residual energy */
res_nrg_2nd = silk_float_MAX;
for( k = 3; k >= 0; k-- ) {
/* Interpolate NLSFs for first half */
silk_interpolate( NLSF0_Q15, psEncC->prev_NLSFq_Q15, NLSF_Q15, k, psEncC->predictLPCOrder );
/* Convert to LPC for residual energy evaluation */
silk_NLSF2A_FLP( a_tmp, NLSF0_Q15, psEncC->predictLPCOrder );
/* Calculate residual energy with LSF interpolation */
silk_LPC_analysis_filter_FLP( LPC_res, a_tmp, x, 2 * subfr_length, psEncC->predictLPCOrder );
res_nrg_interp = (silk_float)(
silk_energy_FLP( LPC_res + psEncC->predictLPCOrder, subfr_length - psEncC->predictLPCOrder ) +
silk_energy_FLP( LPC_res + psEncC->predictLPCOrder + subfr_length, subfr_length - psEncC->predictLPCOrder ) );
/* Determine whether current interpolated NLSFs are best so far */
if( res_nrg_interp < res_nrg ) {
/* Interpolation has lower residual energy */
res_nrg = res_nrg_interp;
psEncC->indices.NLSFInterpCoef_Q2 = (opus_int8)k;
} else if( res_nrg_interp > res_nrg_2nd ) {
/* No reason to continue iterating - residual energies will continue to climb */
break;
}
res_nrg_2nd = res_nrg_interp;
}
}
if( psEncC->indices.NLSFInterpCoef_Q2 == 4 ) {
/* NLSF interpolation is currently inactive, calculate NLSFs from full frame AR coefficients */
silk_A2NLSF_FLP( NLSF_Q15, a, psEncC->predictLPCOrder );
}
silk_assert( psEncC->indices.NLSFInterpCoef_Q2 == 4 ||
( psEncC->useInterpolatedNLSFs && !psEncC->first_frame_after_reset && psEncC->nb_subfr == MAX_NB_SUBFR ) );
}