diff --git a/lib_com/options.h b/lib_com/options.h
index cce0aff4601d055c7f111b7ef353d7739ee978c7..97d2a966f8f8b8b4603300a0c439085c15bf77b9 100644
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -138,7 +138,8 @@
 #ifdef LSF_RE_USE_SECONDARY_CHANNEL
 /*#define LSF_RE_USE_SECONDARY_CHANNEL_REUSEMODE */     /* switch to isolate the reuse mode case */
 #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 ITD_WINNER_GAIN_MODIFY */                     /* ITD optimization - WORK IN PROGRESS */
 /*#define FIX_I4_OL_PITCH*/                             /* fix open-loop pitch used for EVS core switching */
 #define FIX_103_RA_PARAMS_PARAM_BIN_REND                /* Issue 103: Digest room acoustics parameters for Parametric Binaural Renderer*/
diff --git a/lib_enc/ivas_stat_enc.h b/lib_enc/ivas_stat_enc.h
index 6638a8948893cd39c5278f7d59122448c75a1237..5d89d3dab583d377b991a382fbf02d62407ac2b9 100644
--- a/lib_enc/ivas_stat_enc.h
+++ b/lib_enc/ivas_stat_enc.h
@@ -270,6 +270,9 @@ 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 ab4844ab944067f4a519135e05b06574f6d460f5..b5be17f09fe10a4ec554249b8428e23e6c25fa04 100644
--- a/lib_enc/ivas_stereo_dft_enc.c
+++ b/lib_enc/ivas_stereo_dft_enc.c
@@ -520,6 +520,10 @@ 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
@@ -1657,8 +1661,11 @@ void stereo_dft_enc_process(
     if ( hStereoDft->NFFT == STEREO_DFT_N_16k_ENC && hStereoDft->hConfig->ada_wb_res_cod_mode )
     {
         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;
 
@@ -1759,6 +1766,16 @@ 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;
@@ -1767,9 +1784,13 @@ 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;
     }
@@ -1779,12 +1800,28 @@ 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++;
@@ -1804,7 +1841,11 @@ 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++;