bias in LSF quantization towards previously quantized LSFssilk_lsf_quant_with_hysteresis

6 files changed, 205 insertions, 151 deletions

diff --git a/silk/LPC_fit.c b/silk/LPC_fit.c
index cdea4f3a..ac68dedf 100644
--- a/silk/LPC_fit.c
+++ b/silk/LPC_fit.c
@@ -34,14 +34,14 @@ POSSIBILITY OF SUCH DAMAGE.
 /* Convert int32 coefficients to int16 coefs and make sure there's no wrap-around */
 void silk_LPC_fit(
     opus_int16                  *a_QOUT,            /* O    Output signal                                               */
-    opus_int32                    *a_QIN,             /* I/O  Input signal                                                */
+    opus_int32                  *a_QIN,             /* I/O  Input signal                                                */
     const opus_int              QOUT,               /* I    Input Q domain                                              */
     const opus_int              QIN,                /* I    Input Q domain                                              */
     const opus_int              d                   /* I    Filter order                                                */
 )
 {
     opus_int    i, k, idx = 0;
-    opus_int32    maxabs, absval, chirp_Q16;
+    opus_int32  maxabs, absval, chirp_Q16;
 
     /* Limit the maximum absolute value of the prediction coefficients, so that they'll fit in int16 */
     for( i = 0; i < 10; i++ ) {
diff --git a/silk/NLSF_del_dec_quant.c b/silk/NLSF_del_dec_quant.c
index 3895749b..b541e1fc 100644
--- a/silk/NLSF_del_dec_quant.c
+++ b/silk/NLSF_del_dec_quant.c
@@ -32,8 +32,9 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "main.h"
 
 /* Delayed-decision quantizer for NLSF residuals */
-opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns RD value in Q25                     */
-    opus_int8                   indices[],                      /* O    Quantization indices [ order ]              */
+void silk_NLSF_del_dec_quant(

+    opus_int32                  RD_out_Q25[],                   /* O    RD value in Q25                             */
+    opus_int8                   indices[],                      /* O    Quantization indices                        */
     const opus_int16            x_Q10[],                        /* I    Input [ order ]                             */
     const opus_int16            w_Q5[],                         /* I    Weights [ order ]                           */
     const opus_uint8            pred_coef_Q8[],                 /* I    Backward predictor coefs [ order ]          */
@@ -47,7 +48,7 @@ opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns
 {
     opus_int         i, j, nStates, ind_tmp, ind_min_max, ind_max_min, in_Q10, res_Q10;
     opus_int         pred_Q10, diff_Q10, out0_Q10, out1_Q10, rate0_Q5, rate1_Q5;
-    opus_int32       RD_tmp_Q25, min_Q25, min_max_Q25, max_min_Q25, pred_coef_Q16;
+    opus_int32       RD_tmp_Q25, min_max_Q25, max_min_Q25, pred_coef_Q16;
     opus_int         ind_sort[         NLSF_QUANT_DEL_DEC_STATES ];
     opus_int8        ind[              NLSF_QUANT_DEL_DEC_STATES ][ MAX_LPC_ORDER ];
     opus_int16       prev_out_Q10[ 2 * NLSF_QUANT_DEL_DEC_STATES ];
@@ -194,22 +195,7 @@ opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns
         }
     }
 
-    /* last sample: find winner, copy indices and return RD value */
-    ind_tmp = 0;
-    min_Q25 = silk_int32_MAX;
-    for( j = 0; j < 2 * NLSF_QUANT_DEL_DEC_STATES; j++ ) {
-        if( min_Q25 > RD_Q25[ j ] ) {
-            min_Q25 = RD_Q25[ j ];
-            ind_tmp = j;
-        }
-    }
-    for( j = 0; j < order; j++ ) {
-        indices[ j ] = ind[ ind_tmp & ( NLSF_QUANT_DEL_DEC_STATES - 1 ) ][ j ];
-        silk_assert( indices[ j ] >= -NLSF_QUANT_MAX_AMPLITUDE_EXT );
-        silk_assert( indices[ j ] <=  NLSF_QUANT_MAX_AMPLITUDE_EXT );
-    }
-    indices[ 0 ] += silk_RSHIFT( ind_tmp, NLSF_QUANT_DEL_DEC_STATES_LOG2 );
-    silk_assert( indices[ 0 ] <= NLSF_QUANT_MAX_AMPLITUDE_EXT );
-    silk_assert( min_Q25 >= 0 );
-    return min_Q25;
+    /* copy indices and RD values */
+    silk_memcpy( indices, ind, NLSF_QUANT_DEL_DEC_STATES * MAX_LPC_ORDER * sizeof( opus_int8 ) );
+    silk_memcpy( RD_out_Q25, RD_Q25, NLSF_QUANT_DEL_DEC_STATES * sizeof( opus_int32 ) );
 }
diff --git a/silk/NLSF_encode.c b/silk/NLSF_encode.c
index 268b9a19..e0768ae5 100644
--- a/silk/NLSF_encode.c
+++ b/silk/NLSF_encode.c
@@ -1,124 +1,187 @@
-/***********************************************************************
-Copyright (c) 2006-2011, Skype Limited. All rights reserved.
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions
-are met:
-- Redistributions of source code must retain the above copyright notice,
-this list of conditions and the following disclaimer.
-- Redistributions in binary form must reproduce the above copyright
-notice, this list of conditions and the following disclaimer in the
-documentation and/or other materials provided with the distribution.
-- Neither the name of Internet Society, IETF or IETF Trust, nor the
-names of specific contributors, may be used to endorse or promote
-products derived from this software without specific prior written
-permission.
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-POSSIBILITY OF SUCH DAMAGE.
-***********************************************************************/
-
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
-#include "main.h"
-#include "stack_alloc.h"
-
-/***********************/
-/* NLSF vector encoder */
-/***********************/
-opus_int32 silk_NLSF_encode(                                    /* O    Returns RD value in Q25                     */
-          opus_int8             *NLSFIndices,                   /* I    Codebook path vector [ LPC_ORDER + 1 ]      */
-          opus_int16            *pNLSF_Q15,                     /* I/O  (Un)quantized NLSF vector [ LPC_ORDER ]     */
-    const silk_NLSF_CB_struct   *psNLSF_CB,                     /* I    Codebook object                             */
-    const opus_int16            *pW_Q2,                         /* I    NLSF weight vector [ LPC_ORDER ]            */
-    const opus_int              NLSF_mu_Q20,                    /* I    Rate weight for the RD optimization         */
-    const opus_int              nSurvivors,                     /* I    Max survivors after first stage             */
-    const opus_int              signalType                      /* I    Signal type: 0/1/2                          */
-)
-{
-    opus_int         i, s, ind1, bestIndex, prob_Q8, bits_q7;
-    opus_int32       W_tmp_Q9, ret;
-    VARDECL( opus_int32, err_Q24 );
-    VARDECL( opus_int32, RD_Q25 );
-    VARDECL( opus_int, tempIndices1 );
-    VARDECL( opus_int8, tempIndices2 );
-    opus_int16       res_Q10[      MAX_LPC_ORDER ];
-    opus_int16       NLSF_tmp_Q15[ MAX_LPC_ORDER ];
-    opus_int16       W_adj_Q5[     MAX_LPC_ORDER ];
-    opus_uint8       pred_Q8[      MAX_LPC_ORDER ];
-    opus_int16       ec_ix[        MAX_LPC_ORDER ];
-    const opus_uint8 *pCB_element, *iCDF_ptr;
-    const opus_int16 *pCB_Wght_Q9;
-    SAVE_STACK;
-
-    silk_assert( signalType >= 0 && signalType <= 2 );
-    silk_assert( NLSF_mu_Q20 <= 32767 && NLSF_mu_Q20 >= 0 );
-
-    /* NLSF stabilization */
-    silk_NLSF_stabilize( pNLSF_Q15, psNLSF_CB->deltaMin_Q15, psNLSF_CB->order );
-
-    /* First stage: VQ */
-    ALLOC( err_Q24, psNLSF_CB->nVectors, opus_int32 );
-    silk_NLSF_VQ( err_Q24, pNLSF_Q15, psNLSF_CB->CB1_NLSF_Q8, psNLSF_CB->CB1_Wght_Q9, psNLSF_CB->nVectors, psNLSF_CB->order );
-
-    /* Sort the quantization errors */
-    ALLOC( tempIndices1, nSurvivors, opus_int );
-    silk_insertion_sort_increasing( err_Q24, tempIndices1, psNLSF_CB->nVectors, nSurvivors );
-
-    ALLOC( RD_Q25, nSurvivors, opus_int32 );
-    ALLOC( tempIndices2, nSurvivors * MAX_LPC_ORDER, opus_int8 );
-
-    /* Loop over survivors */
-    for( s = 0; s < nSurvivors; s++ ) {
-        ind1 = tempIndices1[ s ];
-
-        /* Residual after first stage */
-        pCB_element = &psNLSF_CB->CB1_NLSF_Q8[ ind1 * psNLSF_CB->order ];
-        pCB_Wght_Q9 = &psNLSF_CB->CB1_Wght_Q9[ ind1 * psNLSF_CB->order ];
-        for( i = 0; i < psNLSF_CB->order; i++ ) {
-            NLSF_tmp_Q15[ i ] = silk_LSHIFT16( (opus_int16)pCB_element[ i ], 7 );
-            W_tmp_Q9 = pCB_Wght_Q9[ i ];
-            res_Q10[ i ] = (opus_int16)silk_RSHIFT( silk_SMULBB( pNLSF_Q15[ i ] - NLSF_tmp_Q15[ i ], W_tmp_Q9 ), 14 );
-            W_adj_Q5[ i ] = silk_DIV32_varQ( (opus_int32)pW_Q2[ i ], silk_SMULBB( W_tmp_Q9, W_tmp_Q9 ), 21 );
-        }
-
-        /* Unpack entropy table indices and predictor for current CB1 index */
-        silk_NLSF_unpack( ec_ix, pred_Q8, psNLSF_CB, ind1 );
-
-        /* Trellis quantizer */
-        RD_Q25[ s ] = silk_NLSF_del_dec_quant( &tempIndices2[ s * MAX_LPC_ORDER ], res_Q10, W_adj_Q5, pred_Q8, ec_ix,
-            psNLSF_CB->ec_Rates_Q5, psNLSF_CB->quantStepSize_Q16, psNLSF_CB->invQuantStepSize_Q6, NLSF_mu_Q20, psNLSF_CB->order );
-
-        /* Add rate for first stage */
-        iCDF_ptr = &psNLSF_CB->CB1_iCDF[ ( signalType >> 1 ) * psNLSF_CB->nVectors ];
-        if( ind1 == 0 ) {
-            prob_Q8 = 256 - iCDF_ptr[ ind1 ];
-        } else {
-            prob_Q8 = iCDF_ptr[ ind1 - 1 ] - iCDF_ptr[ ind1 ];
-        }
-        bits_q7 = ( 8 << 7 ) - silk_lin2log( prob_Q8 );
-        RD_Q25[ s ] = silk_SMLABB( RD_Q25[ s ], bits_q7, silk_RSHIFT( NLSF_mu_Q20, 2 ) );
-    }
-
-    /* Find the lowest rate-distortion error */
-    silk_insertion_sort_increasing( RD_Q25, &bestIndex, nSurvivors, 1 );
-
-    NLSFIndices[ 0 ] = (opus_int8)tempIndices1[ bestIndex ];
-    silk_memcpy( &NLSFIndices[ 1 ], &tempIndices2[ bestIndex * MAX_LPC_ORDER ], psNLSF_CB->order * sizeof( opus_int8 ) );
-
-    /* Decode */
-    silk_NLSF_decode( pNLSF_Q15, NLSFIndices, psNLSF_CB );
-
-    ret = RD_Q25[ 0 ];
-    RESTORE_STACK;
-    return ret;
-}
+/***********************************************************************

+Copyright (c) 2006-2011, Skype Limited. All rights reserved.

+Redistribution and use in source and binary forms, with or without

+modification, are permitted provided that the following conditions

+are met:

+- Redistributions of source code must retain the above copyright notice,

+this list of conditions and the following disclaimer.

+- Redistributions in binary form must reproduce the above copyright

+notice, this list of conditions and the following disclaimer in the

+documentation and/or other materials provided with the distribution.

+- Neither the name of Internet Society, IETF or IETF Trust, nor the

+names of specific contributors, may be used to endorse or promote

+products derived from this software without specific prior written

+permission.

+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE

+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

+POSSIBILITY OF SUCH DAMAGE.

+***********************************************************************/

+

+#ifdef HAVE_CONFIG_H

+#include "config.h"

+#endif

+

+#include "main.h"

+#include "tuning_parameters.h"

+#include "stack_alloc.h"

+

+/***********************/

+/* NLSF vector encoder */

+/***********************/

+opus_int32 silk_NLSF_encode(                                    /* O    Returns RD value in Q25                     */

+          opus_int8             *NLSFIndices,                   /* I    Codebook path vector [ LPC_ORDER + 1 ]      */

+          opus_int16            *pNLSF_Q15,                     /* I/O  (Un)quantized NLSF vector [ LPC_ORDER ]     */

+    const silk_NLSF_CB_struct   *psNLSF_CB,                     /* I    Codebook object                             */

+    const opus_int16            *pW_Q2,                         /* I    NLSF weight vector [ LPC_ORDER ]            */

+    const opus_int16            *pNLSF_Q15_prev,                /* I    Previous Quantized NLSFs[ LPC_ORDER ]       */

+    const opus_int              NLSF_mu_Q20,                    /* I    Rate weight for the RD optimization         */

+    const opus_int              nSurvivors,                     /* I    Max survivors after first stage             */

+    const opus_int              signalType                      /* I    Signal type: 0/1/2                          */

+)

+{

+    opus_int         i, s, ind1, prob_Q8, bits_q7;

+    opus_int32       W_tmp_Q9, R_Q25, ret;

+    VARDECL( opus_int32, err_Q24 );

+    VARDECL( opus_int32, RD_Q25 );

+    VARDECL( opus_int, tempIndices1 );

+    VARDECL( opus_int8, tempIndices2 );

+    VARDECL( opus_int, tempIndices3 );

+    opus_int16       res_Q10[      MAX_LPC_ORDER ];

+    opus_int16       NLSF_tmp_Q15[ MAX_LPC_ORDER ];

+    opus_int16       W_adj_Q5[     MAX_LPC_ORDER ];

+    opus_uint8       pred_Q8[      MAX_LPC_ORDER ];

+    opus_int16       ec_ix[        MAX_LPC_ORDER ];

+    const opus_uint8 *pCB_element, *iCDF_ptr;

+    const opus_int16 *pCB_Wght_Q9;

+    SAVE_STACK;

+

+    silk_assert( signalType >= 0 && signalType <= 2 );

+    silk_assert( NLSF_mu_Q20 <= 32767 && NLSF_mu_Q20 >= 0 );

+

+    /* NLSF stabilization */

+    silk_NLSF_stabilize( pNLSF_Q15, psNLSF_CB->deltaMin_Q15, psNLSF_CB->order );

+

+    /* First stage: VQ */

+    ALLOC( err_Q24, psNLSF_CB->nVectors, opus_int32 );

+    silk_NLSF_VQ( err_Q24, pNLSF_Q15, psNLSF_CB->CB1_NLSF_Q8, psNLSF_CB->CB1_Wght_Q9, psNLSF_CB->nVectors, psNLSF_CB->order );

+

+    /* Sort the quantization errors */

+    ALLOC( tempIndices1, nSurvivors, opus_int );

+    silk_insertion_sort_increasing( err_Q24, tempIndices1, psNLSF_CB->nVectors, nSurvivors );

+

+    ALLOC( RD_Q25, nSurvivors * NLSF_QUANT_DEL_DEC_STATES, opus_int32 );

+    ALLOC( tempIndices2, nSurvivors * NLSF_QUANT_DEL_DEC_STATES * MAX_LPC_ORDER, opus_int8 );

+

+    /* Loop over survivors */

+    for( s = 0; s < nSurvivors; s++ ) {

+        ind1 = tempIndices1[ s ];

+

+        /* Residual after first stage */

+        pCB_element = &psNLSF_CB->CB1_NLSF_Q8[ ind1 * psNLSF_CB->order ];

+        pCB_Wght_Q9 = &psNLSF_CB->CB1_Wght_Q9[ ind1 * psNLSF_CB->order ];

+        for( i = 0; i < psNLSF_CB->order; i++ ) {

+            NLSF_tmp_Q15[ i ] = silk_LSHIFT16( (opus_int16)pCB_element[ i ], 7 );

+            W_tmp_Q9 = pCB_Wght_Q9[ i ];

+            res_Q10[ i ] = (opus_int16)silk_RSHIFT( silk_SMULBB( pNLSF_Q15[ i ] - NLSF_tmp_Q15[ i ], W_tmp_Q9 ), 14 );

+            W_adj_Q5[ i ] = silk_DIV32_varQ( (opus_int32)pW_Q2[ i ], silk_SMULBB( W_tmp_Q9, W_tmp_Q9 ), 21 );

+        }

+

+        /* Unpack entropy table indices and predictor for current CB1 index */

+        silk_NLSF_unpack( ec_ix, pred_Q8, psNLSF_CB, ind1 );

+

+        /* Trellis quantizer */

+        silk_NLSF_del_dec_quant( &RD_Q25[ s * NLSF_QUANT_DEL_DEC_STATES ], &tempIndices2[ s * NLSF_QUANT_DEL_DEC_STATES * MAX_LPC_ORDER ], res_Q10,

+            W_adj_Q5, pred_Q8, ec_ix, psNLSF_CB->ec_Rates_Q5, psNLSF_CB->quantStepSize_Q16, psNLSF_CB->invQuantStepSize_Q6, NLSF_mu_Q20, psNLSF_CB->order );

+

+        /* Add rate for first stage */

+        iCDF_ptr = &psNLSF_CB->CB1_iCDF[ ( signalType >> 1 ) * psNLSF_CB->nVectors ];

+        if( ind1 == 0 ) {

+            prob_Q8 = 256 - iCDF_ptr[ ind1 ];

+        } else {

+            prob_Q8 = iCDF_ptr[ ind1 - 1 ] - iCDF_ptr[ ind1 ];

+        }

+        bits_q7 = ( 8 << 7 ) - silk_lin2log( prob_Q8 );

+        R_Q25 = silk_SMULBB( bits_q7, silk_RSHIFT( NLSF_mu_Q20, 2 ) );

+        for( i = 0; i < NLSF_QUANT_DEL_DEC_STATES; i++ ) {

+            RD_Q25[ s * NLSF_QUANT_DEL_DEC_STATES + i ] = silk_ADD32( RD_Q25[ s * NLSF_QUANT_DEL_DEC_STATES + i ], R_Q25 );

+        }

+    }

+

+    /* Find the lowest rate-distortion error */

+    opus_int nSurvivors2 = nSurvivors;

+    ALLOC( tempIndices3, nSurvivors2, opus_int );

+    silk_insertion_sort_increasing( RD_Q25, tempIndices3, nSurvivors * NLSF_QUANT_DEL_DEC_STATES, nSurvivors2 );

+

+    /* Loop over final survivors and copy indices */

+    if( nSurvivors2 > 1 ) {

+        /* Bias quantizer towards previous quantized coefficients */

+	    opus_int16 pNLSF_Q15_best[ MAX_LPC_ORDER ];

+        opus_int8 NLSFIndices_tmp[ MAX_LPC_ORDER + 1 ];

+        opus_int16 pNLSF_Q15_tmp[ MAX_LPC_ORDER ];

+        opus_int32 RD_Q25_best = silk_int32_MAX;

+        opus_int32 pNLSF_Q15_diff[ MAX_LPC_ORDER ], pNLSF_Q15_err[ MAX_LPC_ORDER ];

+        opus_int32 sum_sqrd_Q22_prev, sum_sqrd_Q22, inv_norm_Q16, inner_prod_Q26, adj_Q16;

+        opus_int64 acc;

+        acc = 0;

+        for( i = 0; i < psNLSF_CB->order; i++ ) {

+            pNLSF_Q15_diff[ i ] = pNLSF_Q15[ i ] - pNLSF_Q15_prev[ i ];

+            acc += (opus_int64)silk_MUL( pNLSF_Q15_diff[ i ], pNLSF_Q15_diff[ i ] ) * pW_Q2[ i ];

+        }

+        sum_sqrd_Q22_prev = (opus_int32)silk_RSHIFT64( acc, 10 );

+        silk_assert( sum_sqrd_Q22_prev >= 0 );

+        inv_norm_Q16 = silk_INVERSE32_varQ( silk_SQRT_APPROX(sum_sqrd_Q22_prev + 1), 24 );

+        for( i = 0; i < psNLSF_CB->order; i++ ) {

+            pNLSF_Q15_diff[ i ] = silk_SMULWW( inv_norm_Q16, pNLSF_Q15_diff[ i ] );

+        }

+        for( s = 0; s < nSurvivors2; s++ ) {

+            NLSFIndices_tmp[ 0 ] = (opus_int8)tempIndices1[ tempIndices3[ s ] >> NLSF_QUANT_DEL_DEC_STATES_LOG2 ];

+            silk_memcpy( &NLSFIndices_tmp[ 1 ], &tempIndices2[ tempIndices3[ s ] * MAX_LPC_ORDER ], psNLSF_CB->order * sizeof( opus_int8 ) );

+            silk_NLSF_decode( pNLSF_Q15_tmp, NLSFIndices_tmp, psNLSF_CB );

+            acc = 0;

+            for( i = 0; i < psNLSF_CB->order; i++ ) {

+                pNLSF_Q15_err[ i ] = pNLSF_Q15[ i ] - pNLSF_Q15_tmp[ i ];

+                acc += (opus_int64)silk_MUL( pNLSF_Q15_err[ i ], pNLSF_Q15_err[ i ] ) * pW_Q2[ i ];

+            }

+            sum_sqrd_Q22 = (opus_int32)silk_RSHIFT64( acc, 10 );

+            silk_assert( sum_sqrd_Q22 >= 0 );

+            inv_norm_Q16 = silk_INVERSE32_varQ( silk_SQRT_APPROX(sum_sqrd_Q22 + 1), 24 );

+

+            /* compute normalized inner product between quantization error and (difference between unquantized LSFs and previous quantized ones) */

+            inner_prod_Q26 = 0;

+            for( i = 0; i < psNLSF_CB->order; i++ ) {

+                pNLSF_Q15_err[ i ] = silk_SMULWW( inv_norm_Q16, pNLSF_Q15_err[ i ] );

+                inner_prod_Q26 += pNLSF_Q15_err[ i ] * pNLSF_Q15_diff[ i ] * pW_Q2[ i ];

+            }

+            if( sum_sqrd_Q22_prev < sum_sqrd_Q22 ) {

+                inner_prod_Q26 = ( (opus_int64)inner_prod_Q26 * sum_sqrd_Q22_prev ) / sum_sqrd_Q22;

+            }

+            /* reduce RD value if quantization error is towards previous quantized LSFs; increase on the other side */

+            adj_Q16 = silk_SMULWB( inner_prod_Q26, SILK_FIX_CONST(-LSF_QUANT_BIAS_TO_PREVIOUS, 6) );

+            RD_Q25[ s ] = silk_SMLAWW( RD_Q25[ s ], RD_Q25[ s ], adj_Q16 );

+

+            if( RD_Q25[ s ] <= RD_Q25_best ) {

+                RD_Q25_best = RD_Q25[ s ];

+                silk_memcpy( NLSFIndices, NLSFIndices_tmp, ( psNLSF_CB->order + 1 ) * sizeof( opus_int8 ) );

+                silk_memcpy( pNLSF_Q15_best, pNLSF_Q15_tmp, psNLSF_CB->order * sizeof( opus_int16 ) );

+            }

+        }

+        silk_memcpy( pNLSF_Q15, pNLSF_Q15_best, psNLSF_CB->order * sizeof( opus_int16 ) );

+        ret = RD_Q25_best;

+    } else {

+        NLSFIndices[ 0 ] = (opus_int8)tempIndices1[ tempIndices3[ 0 ] >> NLSF_QUANT_DEL_DEC_STATES_LOG2 ];

+        silk_memcpy( &NLSFIndices[ 1 ], &tempIndices2[ tempIndices3[ 0 ] * MAX_LPC_ORDER ], psNLSF_CB->order * sizeof( opus_int8 ) );

+        silk_NLSF_decode( pNLSF_Q15, NLSFIndices, psNLSF_CB );

+        ret = RD_Q25[ 0 ];

+    }

+

+    RESTORE_STACK;

+    return ret;

+}

diff --git a/silk/main.h b/silk/main.h
index 94315b47..0587c0e3 100644
--- a/silk/main.h
+++ b/silk/main.h
@@ -332,6 +332,7 @@ opus_int32 silk_NLSF_encode(                                    /* O    Returns
           opus_int16            *pNLSF_Q15,                     /* I/O  Quantized NLSF vector [ LPC_ORDER ]         */
     const silk_NLSF_CB_struct   *psNLSF_CB,                     /* I    Codebook object                             */
     const opus_int16            *pW_QW,                         /* I    NLSF weight vector [ LPC_ORDER ]            */
+    const opus_int16            *pNLSF_Q15_prev,                /* I    Prevoius quantized NLSFs [ LPC_ORDER ]      */
     const opus_int              NLSF_mu_Q20,                    /* I    Rate weight for the RD optimization         */
     const opus_int              nSurvivors,                     /* I    Max survivors after first stage             */
     const opus_int              signalType                      /* I    Signal type: 0/1/2                          */
@@ -348,8 +349,9 @@ void silk_NLSF_VQ(
 );
 
 /* Delayed-decision quantizer for NLSF residuals */
-opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns RD value in Q25                     */
-    opus_int8                   indices[],                      /* O    Quantization indices [ order ]              */
+void silk_NLSF_del_dec_quant(
+    opus_int32                  RD_out_Q25[],                   /* O    RD value in Q25                             */
+    opus_int8                   indices[],                      /* O    Quantization indices                        */
     const opus_int16            x_Q10[],                        /* I    Input [ order ]                             */
     const opus_int16            w_Q5[],                         /* I    Weights [ order ]                           */
     const opus_uint8            pred_coef_Q8[],                 /* I    Backward predictor coefs [ order ]          */
diff --git a/silk/process_NLSFs.c b/silk/process_NLSFs.c
index c27cf030..3ca2ddde 100644
--- a/silk/process_NLSFs.c
+++ b/silk/process_NLSFs.c
@@ -84,7 +84,7 @@ void silk_process_NLSFs(
         }
     }
 
-    silk_NLSF_encode( psEncC->indices.NLSFIndices, pNLSF_Q15, psEncC->psNLSF_CB, pNLSFW_QW,
+    silk_NLSF_encode( psEncC->indices.NLSFIndices, pNLSF_Q15, psEncC->psNLSF_CB, pNLSFW_QW, prev_NLSFq_Q15,
         NLSF_mu_Q20, psEncC->NLSF_MSVQ_Survivors, psEncC->indices.signalType );
 
     /* Convert quantized NLSFs back to LPC coefficients */
diff --git a/silk/tuning_parameters.h b/silk/tuning_parameters.h
index cbf68bac..22a2df1f 100644
--- a/silk/tuning_parameters.h
+++ b/silk/tuning_parameters.h
@@ -50,7 +50,7 @@ extern "C"
 /* Linear prediction */
 /*********************/
 
-/* LPC analysis defines: regularization and bandwidth expansion */
+/* LPC analysis regularization */
 #define FIND_LPC_COND_FAC                               1e-5f
 
 /***********************/
@@ -128,6 +128,9 @@ extern "C"
 /* subframe smoothing coefficient for HarmBoost, HarmShapeGain, Tilt (lower -> more smoothing) */
 #define SUBFR_SMTH_COEF                                 0.4f
 
+/* bias in LSF quantization towards previous quantized LSFs (0.0...1.0) */
+#define LSF_QUANT_BIAS_TO_PREVIOUS                      0.3f
+
 /* parameters defining the R/D tradeoff in the residual quantizer */
 #define LAMBDA_OFFSET                                   1.2f
 #define LAMBDA_SPEECH_ACT                               -0.2f