diff --git a/lib_com/options.h b/lib_com/options.h
index 0a966bc252c7252d2a4507c4d4393f63e2ef3c3e..ef37e3e3b04b838c39db76efeac480655bd98697 100755
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -143,7 +143,8 @@
 #define BITSTREAM_INDICES_MEMORY                        /* Don't count memory for bitstream Indice at the encoder - it is a temporary solution for development only */
 #endif
 
-#define DISABLE_ADAP_RES_COD_TMP                        /* temporary fix for IVAS-403, disables adaptive residual coding */
+/*#define DISABLE_ADAP_RES_COD_TMP*/                    /* temporary fix for IVAS-403, disables adaptive residual coding */
+#define ADAP_OPT                                        /* Issue 69: optimized the adap algorithm */
 /*#define FIX_I4_OL_PITCH*/                             /* fix open-loop pitch used for EVS core switching */
 
 #ifdef IND_LIST_DYN
diff --git a/lib_enc/ivas_stat_enc.h b/lib_enc/ivas_stat_enc.h
index 5ab31a5b473abfe588479c1265133573d707a073..b3a6e6c16b3d39ea81ffc08991bd66a4c4185b8d 100644
--- a/lib_enc/ivas_stat_enc.h
+++ b/lib_enc/ivas_stat_enc.h
@@ -256,6 +256,9 @@ typedef struct stereo_dft_enc_data_struct
     float res_cod_NRG_S[STEREO_DFT_BAND_MAX];
     float res_cod_SNR_M[STEREO_DFT_BAND_MAX];
     float old_snr;
+#ifdef ADAP_OPT
+    int16_t first_frm_flag; /* ADAP first frame flag */
+#endif
 
     /* flags and data for adaptive wideband residual coding */
     float res_dmx_ratio_lt;                /* long term energy ratio between RES and DMX */
diff --git a/lib_enc/ivas_stereo_dft_enc.c b/lib_enc/ivas_stereo_dft_enc.c
index e533ff4c4cf7c269b8b560943fa303976cfa519c..014f23ed9f72e40ea0b4072473001cc0bf0113eb 100644
--- a/lib_enc/ivas_stereo_dft_enc.c
+++ b/lib_enc/ivas_stereo_dft_enc.c
@@ -508,6 +508,10 @@ void stereo_dft_enc_reset(
     hStereoDft->hItd->prev_itd1 = 0;
     hStereoDft->hItd->prev_itd2 = 0;
 
+#ifdef ADAP_OPT
+    hStereoDft->first_frm_flag = 1;
+#endif
+
 #ifdef DEBUG_MODE_DFT
     hStereoDft->verbose = 1;
 #endif
@@ -1648,7 +1652,11 @@ void stereo_dft_enc_process(
     {
         stereo_dft_enc_get_res_cod_mode_flag( hStereoDft, res_nrg_all_curr, dmx_nrg_all_curr, &res_dmx_ratio, &frame_nrg_ratio );
 
+#ifdef ADAP_OPT
+        if ( hStereoDft->res_cod_sw_flag )
+#else
         if ( hStereoDft->res_cod_mode[k_offset] == STEREO_DFT_RES_COD_OFF || hStereoDft->res_cod_sw_flag )
+#endif
         {
             int16_t res_cod_band_max;
 
@@ -1749,6 +1757,16 @@ static void stereo_dft_enc_get_res_cod_mode_flag(
     }
 
     /* Calculate long term energy ratio between residual signal and downmix signal */
+#ifdef ADAP_OPT
+    if ( fast_update_flag )
+    {
+        hStereoDft->res_dmx_ratio_lt = *res_dmx_ratio * 0.2f + hStereoDft->res_dmx_ratio_lt * 0.8f;
+    }
+    else
+    {
+        hStereoDft->res_dmx_ratio_lt = *res_dmx_ratio * 0.05f + hStereoDft->res_dmx_ratio_lt * 0.95f;
+    }
+#else
     if ( fast_update_flag )
     {
         hStereoDft->res_dmx_ratio_lt = *res_dmx_ratio * 0.5f + hStereoDft->res_dmx_ratio_lt * 0.5f;
@@ -1757,9 +1775,14 @@ static void stereo_dft_enc_get_res_cod_mode_flag(
     {
         hStereoDft->res_dmx_ratio_lt = *res_dmx_ratio * 0.1f + hStereoDft->res_dmx_ratio_lt * 0.9f;
     }
+#endif
 
     /*Get the  residual signal coding initial flag */
+#ifdef ADAP_OPT
+    if ( hStereoDft->res_dmx_ratio_lt > 0.01f )
+#else
     if ( hStereoDft->res_dmx_ratio_lt > 0.075f )
+#endif
     {
         res_cod_mode_flag = 1;
     }
@@ -1769,12 +1792,28 @@ static void stereo_dft_enc_get_res_cod_mode_flag(
     }
 
     /* Get the residual signal coding flag */
+#ifdef ADAP_OPT
+    if ( hStereoDft->first_frm_flag )
+    {
+        prev_res_cod_mode_flag = res_cod_mode_flag;
+        hStereoDft->first_frm_flag = 0;
+    }
+    else
+    {
+        prev_res_cod_mode_flag = hStereoDft->res_cod_mode[STEREO_DFT_OFFSET - 1];
+    }
+#else
     prev_res_cod_mode_flag = hStereoDft->res_cod_mode[STEREO_DFT_OFFSET - 1];
+#endif
     if ( res_cod_mode_flag != prev_res_cod_mode_flag )
     {
         if ( prev_res_cod_mode_flag == 1 )
         {
+#ifdef ADAP_OPT
+            if ( hStereoDft->hangover_cnt0 < 5 && hStereoDft->last_res_cod_mode_modify_flag == 0 && fast_update_flag == 0 )
+#else
             if ( hStereoDft->hangover_cnt0 < 3 && hStereoDft->last_res_cod_mode_modify_flag == 0 && fast_update_flag == 0 )
+#endif
             {
                 res_cod_mode_flag = prev_res_cod_mode_flag;
                 hStereoDft->hangover_cnt0++;
@@ -1794,7 +1833,11 @@ static void stereo_dft_enc_get_res_cod_mode_flag(
             }
             else
             {
+#ifdef ADAP_OPT
+                if ( hStereoDft->hangover_cnt1 < 5 )
+#else
                 if ( hStereoDft->hangover_cnt1 < 3 )
+#endif
                 {
                     res_cod_mode_flag = prev_res_cod_mode_flag;
                     hStereoDft->hangover_cnt1++;