diff --git a/lib_com/ivas_cov_smooth_fx.c b/lib_com/ivas_cov_smooth_fx.c
index 3a93ed1f577c0a8f2536607f5d25256674bd4f5c..9a8de3c1f055c1e3a119181c3c404a3a903242a7 100644
--- a/lib_com/ivas_cov_smooth_fx.c
+++ b/lib_com/ivas_cov_smooth_fx.c
@@ -42,6 +42,8 @@
  *-----------------------------------------------------------------------------------------*/
 
 #define BAND_SMOOTH_REST_START_IDX ( 2 )
+#define ONEeN20_Q97                0x5E728433 // 1e-20 in Q97  1.584.563.251
+
 
 /*-----------------------------------------------------------------------------------------*
  * Function ivas_calculate_update_factor_fx()
@@ -87,9 +89,10 @@ static void ivas_calculate_smoothning_factor_fx(
     move16();
 
     tmp = BASOP_Util_Divide3232_Scale( update_factor, L_shl( L_deposit_l( min_pool_size ), Q22 ), &exp_diff ); // Q(31 - exp_diff)
-    *Smoothing_factor = L_shl_sat( L_deposit_l( tmp ), add( Q16, exp_diff ) );                                 // Q31
+    *Smoothing_factor = L_shl_sat( L_deposit_h( tmp ), exp_diff );                                             // Q31
     move32();
 
+
     IF( NE_32( smooth_mode, COV_SMOOTH_MC ) )
     {
         IF( LT_32( ivas_total_brate, IVAS_24k4 ) )
@@ -264,19 +267,17 @@ void ivas_spar_covar_smooth_enc_close_fx(
     return;
 }
 
-
 /*-----------------------------------------------------------------------------------------*
  * Function ivas_compute_smooth_cov_fx()
  *
  * Compute smooth covariance real/imag.
  *-----------------------------------------------------------------------------------------*/
-
 static void ivas_compute_smooth_cov_fx(
     ivas_cov_smooth_state_t *hCovState,
     ivas_filterbank_t *pFb,
     Word32 *pCov_buf[IVAS_SPAR_MAX_CH][IVAS_SPAR_MAX_CH],       // i/o: Q(q_cov[i][j])
     Word32 *pPrior_cov_buf[IVAS_SPAR_MAX_CH][IVAS_SPAR_MAX_CH], // i: hCovState->q_cov_real_per_band[i][j][k]
-    const Word32 fac,
+    const Word32 fac,                                           // i: ONEeN20_Q97 (1e-20 in Q97)
     const Word16 start_band,
     const Word16 end_band,
     const Word16 num_ch,
@@ -285,10 +286,15 @@ static void ivas_compute_smooth_cov_fx(
 {
     Word16 i, j, k;
     Word16 prev_idx = hCovState->prior_bank_idx;
-    Word32 factor = 0, L_tmp, L_tmp1;
+    Word32 factor = 0, L_tmp0, L_tmp1;
+
+    const Word16 q_fac = 97;
+    const Word16 fac_e = sub( Q31, q_fac );
+
+    Word16 cov_buf_e;
+
     Word16 sm_b;
     Word16 non_sm_b_idx;
-    Word16 q_tmp[IVAS_MAX_NUM_BANDS];
 
     sm_b = BAND_SMOOTH_REST_START_IDX;
     move16();
@@ -296,7 +302,6 @@ static void ivas_compute_smooth_cov_fx(
     move32();
 
     assert( end_band <= pFb->filterbank_num_bands );
-
     test();
     IF( EQ_16( prev_idx, -1 ) || EQ_16( transient_det[1], 1 ) )
     {
@@ -311,9 +316,11 @@ static void ivas_compute_smooth_cov_fx(
         {
             FOR( k = start_band; k < end_band; k++ )
             {
-                L_tmp = Mpy_32_32( hCovState->pSmoothing_factor_fx[k], fac );                                                        // (Q31, Q31) -> Q31
-                pCov_buf[i][i][k] = L_add( pCov_buf[i][i][k], L_shl( L_tmp, sub( hCovState->q_cov_real_per_band[i][i][k], Q31 ) ) ); // hCovState->q_cov_real_per_band[i][j][k]
+                /* ref: pCov_buf[i][i][k] += ( hCovState->pSmoothing_factor[k] * fac ); */
+                pCov_buf[i][i][k] = BASOP_Util_Add_Mant32Exp( pCov_buf[i][i][k], sub( Q31, q_cov[i][i] ), Mpy_32_32( hCovState->pSmoothing_factor_fx[k], fac ), fac_e, &cov_buf_e );
                 move32();
+                hCovState->q_cov_real_per_band[i][i][k] = sub( Q31, cov_buf_e );
+                move16();
             }
         }
     }
@@ -326,38 +333,45 @@ static void ivas_compute_smooth_cov_fx(
             {
                 IF( EQ_16( i, j ) )
                 {
-                    factor = fac; // Q31
+                    factor = fac; // Q97
                     move32();
                 }
                 ELSE
                 {
-                    factor = 0;
+                    factor = 0; // Q97
                     move32();
                 }
 
-                set16_fx( q_tmp, q_cov[i][j], sub( end_band, start_band ) );
                 FOR( k = start_band; k < non_sm_b_idx; k++ )
                 {
-                    L_tmp = Mpy_32_32( hCovState->pSmoothing_factor_fx[k], pCov_buf[i][j][k] );                                                                                   // (Q31, q_cov[i][j]) -> q_cov[i][j]
-                    L_tmp1 = Mpy_32_32( L_sub( ONE_IN_Q31, hCovState->pSmoothing_factor_fx[k] ), pPrior_cov_buf[i][j][k] );                                                       // (Q31, hCovState->q_cov_real_per_band[i][j][k]) -> hCovState->q_cov_real_per_band[i][j][k]
-                    pCov_buf[i][j][k] = BASOP_Util_Add_Mant32Exp( L_tmp, sub( Q31, q_cov[i][j] ), L_tmp1, sub( Q31, hCovState->q_prior_cov_real_per_band[i][j][k] ), &q_tmp[k] ); // Q(31 - q_tmp[k])
+                    /* ref: pCov_buf[i][j][k] = pPrior_cov_buf[i][j][k] + ( hCovState->pSmoothing_factor[k] * ( pCov_buf[i][j][k] - pPrior_cov_buf[i][j][k] + factor ) ); */
+                    /* mod: pCov_buf[i][j][k] = pCov_buf[i][j][k] * hCovState->pSmoothing_factor[k] +
+                                                    pPrior_cov_buf[i][j][k] * (1.0 - hCovState->pSmoothing_factor[k]) +
+                                                        factor * hCovState->pSmoothing_factor[k] ); */
+                    L_tmp0 = Mpy_32_32( hCovState->pSmoothing_factor_fx[k], pCov_buf[i][j][k] );                            // q_tmp0: q_cov[i][j]                                                                                  // (Q31, q_cov[i][j]) -> q_cov[i][j]
+                    L_tmp1 = Mpy_32_32( L_sub( ONE_IN_Q31, hCovState->pSmoothing_factor_fx[k] ), pPrior_cov_buf[i][j][k] ); // q_tmp1: hCovState->q_prior_cov_real_per_band[i][j][k]
+                    L_tmp0 = BASOP_Util_Add_Mant32Exp( L_tmp0, sub( Q31, q_cov[i][j] ), L_tmp1, sub( Q31, hCovState->q_prior_cov_real_per_band[i][j][k] ), &cov_buf_e );
+                    pCov_buf[i][j][k] = BASOP_Util_Add_Mant32Exp( L_tmp0, cov_buf_e, Mpy_32_32( hCovState->pSmoothing_factor_fx[k], factor ), fac_e, &cov_buf_e );
                     move32();
-                    q_tmp[k] = sub( Q31, q_tmp[k] ); // Q of pConv_buf[i][j][k] is now q_tmp[k]
+                    hCovState->q_cov_real_per_band[i][j][k] = sub( Q31, cov_buf_e ); // Q of pCov_buf[i][j][k]
+                    move16();
+                }
+                FOR( ; k < end_band; k++ )
+                {
+                    hCovState->q_cov_real_per_band[i][j][k] = q_cov[i][j];
                     move16();
-                    L_tmp = L_shl( Mpy_32_32( hCovState->pSmoothing_factor_fx[k], factor ), sub( q_tmp[k], Q31 ) ); // ((Q31, Q31) -> Q31) -> q_tmp[k]
-                    pCov_buf[i][j][k] = L_add( pCov_buf[i][j][k], L_tmp );                                          // q_tmp[k]
-                    move32();
                 }
-                Copy( q_tmp, hCovState->q_cov_real_per_band[i][j], sub( end_band, start_band ) ); // Q of pCov_buf[i][j][k] is hCovState->q_cov_real_per_band[i][j][j]
             }
         }
         FOR( i = 0; i < num_ch; i++ )
         {
             FOR( k = non_sm_b_idx; k < end_band; k++ )
             {
-                L_tmp = Mpy_32_32( hCovState->pSmoothing_factor_fx[k], fac );                                                        // (Q31, Q31) -> Q31
-                pCov_buf[i][i][k] = L_add( pCov_buf[i][i][k], L_shl( L_tmp, sub( hCovState->q_cov_real_per_band[i][i][k], Q31 ) ) ); // hCovState->q_cov_real_per_band[i][j][j]
+                /* ref: pCov_buf[i][i][k] += ( hCovState->pSmoothing_factor[k] * fac ); */
+                pCov_buf[i][i][k] = BASOP_Util_Add_Mant32Exp( pCov_buf[i][i][k], sub( Q31, q_cov[i][i] ), Mpy_32_32( hCovState->pSmoothing_factor_fx[k], fac ), fac_e, &cov_buf_e );
                 move32();
+                hCovState->q_cov_real_per_band[i][i][k] = sub( Q31, cov_buf_e ); // Q of pCov_buf[i][i][k]
+                move16();
             }
         }
     }
@@ -369,28 +383,29 @@ static void ivas_compute_smooth_cov_fx(
             {
                 IF( EQ_16( i, j ) )
                 {
-                    factor = fac; // Q31
+                    factor = fac; // Q97
                     move32();
                 }
                 ELSE
                 {
-                    factor = 0;
+                    factor = 0; // Q97
                     move32();
                 }
 
                 FOR( k = start_band; k < end_band; k++ )
                 {
-                    L_tmp = Mpy_32_32( hCovState->pSmoothing_factor_fx[k], pCov_buf[i][j][k] );                                                                                   // (Q31, q_cov[i][j]) -> q_cov[i][j]
-                    L_tmp1 = Mpy_32_32( L_sub( ONE_IN_Q31, hCovState->pSmoothing_factor_fx[k] ), pPrior_cov_buf[i][j][k] );                                                       // (Q31, hCovState->q_cov_real_per_band[i][j][k]) -> hCovState->q_cov_real_per_band[i][j][k]
-                    pCov_buf[i][j][k] = BASOP_Util_Add_Mant32Exp( L_tmp, sub( Q31, q_cov[i][j] ), L_tmp1, sub( Q31, hCovState->q_prior_cov_real_per_band[i][j][k] ), &q_tmp[k] ); // Q(31 - q_tmp[k])
+                    /* ref: pCov_buf[i][j][k] = pPrior_cov_buf[i][j][k] + ( hCovState->pSmoothing_factor[k] * ( pCov_buf[i][j][k] - pPrior_cov_buf[i][j][k] + factor ) ); */
+                    /* mod: pCov_buf[i][j][k] = pCov_buf[i][j][k] * hCovState->pSmoothing_factor[k] +
+                                                pPrior_cov_buf[i][j][k] * (1.0 - hCovState->pSmoothing_factor[k]) +
+                                                factor * hCovState->pSmoothing_factor[k] ); */
+                    L_tmp0 = Mpy_32_32( hCovState->pSmoothing_factor_fx[k], pCov_buf[i][j][k] );                            // q_tmp0: q_cov[i][j]                                                                                  // (Q31, q_cov[i][j]) -> q_cov[i][j]
+                    L_tmp1 = Mpy_32_32( L_sub( ONE_IN_Q31, hCovState->pSmoothing_factor_fx[k] ), pPrior_cov_buf[i][j][k] ); // q_tmp1: hCovState->q_prior_cov_real_per_band[i][j][k]
+                    L_tmp0 = BASOP_Util_Add_Mant32Exp( L_tmp0, sub( Q31, q_cov[i][j] ), L_tmp1, sub( Q31, hCovState->q_prior_cov_real_per_band[i][j][k] ), &cov_buf_e );
+                    pCov_buf[i][j][k] = BASOP_Util_Add_Mant32Exp( L_tmp0, cov_buf_e, Mpy_32_32( hCovState->pSmoothing_factor_fx[k], factor ), fac_e, &cov_buf_e );
                     move32();
-                    q_tmp[k] = sub( Q31, q_tmp[k] ); // Q of pConv_buf[i][j][k] is now q_tmp[k]
+                    hCovState->q_cov_real_per_band[i][j][k] = sub( Q31, cov_buf_e ); // Q of pCov_buf[i][j][k]
                     move16();
-                    L_tmp = L_shl( Mpy_32_32( hCovState->pSmoothing_factor_fx[k], factor ), sub( q_tmp[k], Q31 ) ); // ((Q31, Q31) -> Q31) -> q_tmp[k]
-                    pCov_buf[i][j][k] = L_add( pCov_buf[i][j][k], L_tmp );                                          // q_tmp[k]
-                    move32();
                 }
-                Copy( q_tmp, hCovState->q_cov_real_per_band[i][j], sub( end_band, start_band ) ); // Q of pCov_buf[i][j][k] is hCovState->q_cov_real_per_band[i][j][j]
             }
         }
     }
@@ -418,7 +433,7 @@ void ivas_cov_smooth_process_fx(
     Word16 i, j, k;
     Word16 num_bands = sub( end_band, start_band );
 
-    ivas_compute_smooth_cov_fx( hCovState, pFb, cov_real, hCovState->pPrior_cov_real_fx, 0, start_band, end_band, num_ch, transient_det, q_cov );
+    ivas_compute_smooth_cov_fx( hCovState, pFb, cov_real, hCovState->pPrior_cov_real_fx, ONEeN20_Q97, start_band, end_band, num_ch, transient_det, q_cov );
 
     FOR( i = 0; i < num_ch; i++ )
     {