diff --git a/lib_com/options.h b/lib_com/options.h
index 8a35f4f6f43c91477f71e36fa50b8837baa11669..d62cb1880b1ed327b96d3f6f32b3afc6e2a12841 100755
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -173,6 +173,8 @@
 #define FIX_ISM_METADATA_READER                         /* Issue 211: make ISM metadata file reader robust against invalid files */
 #define FIX_GET_DELAY_RETURN                            /* Issue 223: change return data type in function get_delay() */
 
+/* NTT switches */
+#define NTT_REDUC_COMP_POC                              /* Contribution  : Complexity reduction of phase spectrum in stereo downmix*/
 
 /* ################## End DEVELOPMENT switches ######################### */
 /* clang-format on */
diff --git a/lib_enc/ivas_stereo_dmx_evs.c b/lib_enc/ivas_stereo_dmx_evs.c
index a6773bc64c7408737920af691d03a3cc51bd87e1..b0ec2f1c8ed0f22c5b6085ca389a48a288cfa833 100644
--- a/lib_enc/ivas_stereo_dmx_evs.c
+++ b/lib_enc/ivas_stereo_dmx_evs.c
@@ -155,11 +155,23 @@ static void calc_poc(
     const float *s;
     float *P;
     float tmp1, tmp2, Lr, Li, Rr, Ri, gamma, igamma, iN;
+
+#ifdef NTT_REDUC_COMP_POC
+    float specPOr[L_FRAME48k / 2 + 1], specPOi[L_FRAME48k / 2]; /*real and imaginary values for searching phase angle*/
+    float tmpPOC1[L_FRAME48k], tmpPOC2[L_FRAME48k];
+    float rfft_buf[L_FRAME48k];
+    int16_t step, bias;
+    int16_t mult_angle;
+    int16_t j;
+    int16_t end;
+#else
     float specPOr[L_FRAME48k], specPOi[L_FRAME48k];
     float tmpPOC1[L_FRAME48k], tmpPOC2[L_FRAME48k];
     float rfft_buf[L_FRAME48k];
     int16_t step, bias;
     int16_t i_for;
+#endif
+
     int16_t cos_step, cos_max;
     float eps_cos, eps_sin, EPS;
 
@@ -170,9 +182,171 @@ static void calc_poc(
     P = hPOC->P;
     n0 = input_frame / 2;
     itdLR = hPOC->itdLR;
+
     igamma = STEREO_DMX_EVS_POC_GAMMA * iN;
     gamma = 1.0f - igamma;
 
+#ifdef NTT_REDUC_COMP_POC /*apploximation of phase angle on an unit circle without using sqrt()*/
+
+    step = 1;
+    bias = 0;
+    cos_step = 2;
+    cos_max = n0;
+    mult_angle = 3;
+
+    if ( input_frame == L_FRAME16k )
+    {
+        step = 3;
+        bias = 1;
+        cos_step = 4;
+        cos_max = input_frame;
+        mult_angle = 2; /*****/
+    }
+    if ( input_frame == L_FRAME32k )
+    {
+        mult_angle = 2;
+    }
+
+    end = min( n0, 320 );
+    specPOr[0] = sign( specLr[0] * specRr[0] ) * wnd[bias];
+    specPOi[0] = 0.0f;
+    EPS = hPOC->eps;
+    if ( input_frame == L_FRAME48k )
+    {
+        for ( i = 1; i < n0 / 2; i++ )
+        {
+            eps_cos = s[cos_max - i * cos_step /*cos_max - i_for*/] * EPS;
+            eps_sin = s[i * cos_step /*i_for*/] * EPS;
+            Lr = specLr[i] + specRr[i] * eps_cos + specRi[i] * eps_sin;
+            Li = specLi[i] - specRr[i] * eps_sin + specRi[i] * eps_cos;
+            Rr = specRr[i] + specLr[i] * eps_cos + specLi[i] * eps_sin;
+            Ri = specRi[i] - specLr[i] * eps_sin + specLi[i] * eps_cos;
+
+            specPOr[i] = ( Lr * Rr + Li * Ri );
+            specPOi[i] = ( Lr * Ri - Li * Rr );
+            j = n0 - i;
+            if ( j < 320 )
+            {
+                Lr = specLr[j] - specRr[j] * eps_cos + specRi[j] * eps_sin;
+                Li = specLi[j] - specRr[j] * eps_sin - specRi[j] * eps_cos;
+                Rr = specRr[j] - specLr[j] * eps_cos + specLi[j] * eps_sin;
+                Ri = specRi[j] - specLr[j] * eps_sin - specLi[j] * eps_cos;
+
+                specPOr[j] = ( Lr * Rr + Li * Ri );
+                specPOi[j] = ( Lr * Ri - Li * Rr );
+            }
+        }
+    }
+    else /* 16kHz and 32 kHz*/
+    {
+        for ( i = 1; i < n0 / 2; i++ )
+        {
+            eps_cos = s[cos_max - i * cos_step /*cos_max - i_for*/] * EPS;
+            eps_sin = s[i * cos_step /*i_for*/] * EPS;
+
+            Lr = specLr[i] + specRr[i] * eps_cos + specRi[i] * eps_sin;
+            Li = specLi[i] - specRr[i] * eps_sin + specRi[i] * eps_cos;
+            Rr = specRr[i] + specLr[i] * eps_cos + specLi[i] * eps_sin;
+            Ri = specRi[i] - specLr[i] * eps_sin + specLi[i] * eps_cos;
+            specPOr[i] = ( Lr * Rr + Li * Ri );
+            specPOi[i] = ( Lr * Ri - Li * Rr );
+
+            j = n0 - i;
+            Lr = specLr[j] - specRr[j] * eps_cos + specRi[j] * eps_sin;
+            Li = specLi[j] - specRr[j] * eps_sin - specRi[j] * eps_cos;
+            Rr = specRr[j] - specLr[j] * eps_cos + specLi[j] * eps_sin;
+            Ri = specRi[j] - specLr[j] * eps_sin - specLi[j] * eps_cos;
+            specPOr[j] = ( Lr * Rr + Li * Ri );
+            specPOi[j] = ( Lr * Ri - Li * Rr );
+        }
+    }
+    {
+        /* i=n0/2*/
+        Lr = specLr[i] + specRi[i] * EPS;
+        Li = specLi[i] - specRr[i] * EPS;
+        Rr = specRr[i] + specLi[i] * EPS;
+        Ri = specRi[i] - specLr[i] * EPS;
+        specPOr[i] = ( Lr * Rr + Li * Ri );
+        specPOi[i] = ( Lr * Ri - Li * Rr );
+    }
+    /* complex spectrum (specPOr[i], specPOi[i]) are placed on an unit circle without using  srqt()*/
+    for ( i = 1; i < 10; i++ ) /*search from 4 angles */
+    {
+        tmp1 = wnd[i * step + bias] * gamma;
+
+        specPOr[i] = sign( specPOr[i] ) * 0.866f * tmp1; /* low angles are more frequent for low frequency */
+        specPOi[i] = sign( specPOi[i] ) * 0.5f * tmp1;
+        gamma -= igamma;
+    }
+    for ( ; i < n0 >> 4; i++ ) /*search from 4 angles */
+    {
+        tmp1 = wnd[i * step + bias] * gamma * 0.7071f;
+
+        specPOr[i] = sign( specPOr[i] ) * tmp1;
+        specPOi[i] = sign( specPOi[i] ) * tmp1; /* low accuracy is adequate for low frequency */
+        gamma -= igamma;
+    }
+
+    for ( ; i < n0 >> 3; i++ ) /* binary search from 8 angles */
+    {
+        tmp1 = wnd[i * step + bias] * gamma;
+
+        if ( ( specPOr[i] - specPOi[i] ) * ( specPOr[i] + specPOi[i] ) > 0 )
+        {
+            specPOr[i] = sign( specPOr[i] ) * tmp1 * /*0.923880f*/ s[120 * mult_angle]; /*  cos(PI/8)*/
+            specPOi[i] = sign( specPOi[i] ) * tmp1 * /*0.382683f*/ s[40 * mult_angle];
+        }
+        else
+        {
+            specPOr[i] = sign( specPOr[i] ) * tmp1 * /*0.382683f*/ s[40 * mult_angle]; /*  cos(PI*3/8)*/
+            specPOi[i] = sign( specPOi[i] ) * tmp1 * /*0.923880f*/ s[120 * mult_angle];
+        }
+        gamma -= igamma;
+    }
+    for ( ; i < end; i++ ) /* binary search from 16 angles */
+    {
+        tmp1 = wnd[i * step + bias] * gamma;
+        if ( ( specPOr[i] - specPOi[i] ) * ( specPOr[i] + specPOi[i] ) > 0 )
+        {
+            if ( ( specPOr[i] * 0.414213f - specPOi[i] ) * ( specPOr[i] * 0.414213f + specPOi[i] ) > 0 ) /*tan(PI/8)*/
+            {
+                specPOr[i] = sign( specPOr[i] ) * tmp1 /*0.980785f */ * s[140 * mult_angle]; /* cos(PI/16)*/
+                specPOi[i] = sign( specPOi[i] ) * tmp1 /*0.195090f */ * s[20 * mult_angle];
+            }
+            else
+            {
+                specPOr[i] = sign( specPOr[i] ) * tmp1 /* 0.831470f */ * s[100 * mult_angle]; /*cos(PI*3/16)*/
+                specPOi[i] = sign( specPOi[i] ) * tmp1 /* 0.555570f*/ * s[60 * mult_angle];
+            }
+        }
+        else
+        {
+            if ( ( specPOr[i] - specPOi[i] * 0.414213f ) * ( specPOr[i] + specPOi[i] * 0.414213f ) > 0 ) /*tan(PI/8)*/
+            {
+                specPOr[i] = sign( specPOr[i] ) * tmp1 /** 0.555570f*/ * s[60 * mult_angle]; /*cos(PI*5/16)*/
+                specPOi[i] = sign( specPOi[i] ) * tmp1 /** 0.831470f*/ * s[100 * mult_angle];
+            }
+            else
+            {
+                specPOr[i] = sign( specPOr[i] ) * tmp1 /** 0.195090f*/ * s[20 * mult_angle]; /*cos(PI*7/16)*/
+                specPOi[i] = sign( specPOi[i] ) * tmp1 /** 0.980785f*/ * s[140 * mult_angle];
+            }
+        }
+        gamma -= igamma;
+    }
+
+    if ( i < n0 )
+    {
+        gamma -= igamma * ( n0 - 320 );
+    }
+    for ( ; i < n0; i++ ) /*neglect higher frequency bins when 48 kHz samplng*/
+    {
+        specPOr[i] = 0.f;
+        specPOi[i] = 0.f;
+    }
+    specPOr[n0] = sign( specLr[n0] * specRr[n0] ) * wnd[i * step + bias] * gamma;
+
+#else /*NTT_REDUC_COMP_POC*/
     if ( input_frame == L_FRAME16k )
     {
         step = 3;
@@ -199,7 +373,6 @@ static void calc_poc(
         cos_step = 2;
         cos_max = n0;
     }
-
     for ( i = 1; i < n0 / 2; i++ )
     {
         Lr = specLr[i];
@@ -213,6 +386,7 @@ static void calc_poc(
         Li += ( -specRr[i] * eps_sin + specRi[i] * eps_cos );
         Rr += ( specLr[i] * eps_cos + specLi[i] * eps_sin );
         Ri += ( -specLr[i] * eps_sin + specLi[i] * eps_cos );
+
         tmp1 = wnd[i * step + bias] * gamma / ( sqrtf( ( ( Lr * Lr + Li * Li ) ) * ( ( Rr * Rr + Ri * Ri ) ) ) + EPS );
 
         specPOr[i] = ( Lr * Rr + Li * Ri ) * tmp1;
@@ -245,6 +419,7 @@ static void calc_poc(
     }
 
     specPOr[n0] = sign( specLr[i] ) * sign( specRr[i] ) * wnd[i * step + bias] * gamma;
+#endif
 
     rfft_buf[0] = specPOr[0];
     rfft_buf[1] = specPOr[n0];