From 15eeaa14adea56366265d954eab302a8b248fedd Mon Sep 17 00:00:00 2001
From: Sandesh Venkatesh <sandesh.venkatesh@ittiam.com>
Date: Thu, 20 Mar 2025 18:50:36 +0530
Subject: [PATCH] Fix for 3GPP issue 1339: Artifact in IGF part for first
 active frame after DTX period in MDCT-Stereo

Link #1339
---
 lib_enc/ivas_stereo_mdct_core_enc_fx.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/lib_enc/ivas_stereo_mdct_core_enc_fx.c b/lib_enc/ivas_stereo_mdct_core_enc_fx.c
index b68578542..a73120286 100644
--- a/lib_enc/ivas_stereo_mdct_core_enc_fx.c
+++ b/lib_enc/ivas_stereo_mdct_core_enc_fx.c
@@ -360,6 +360,32 @@ void stereo_mdct_core_enc_fx(
         }
         q_spec = sub( Q31, q_spec );
 
+        /*find headroom to increase precision*/
+        Word16 hdrm_min = MAX_16;
+        move16();
+        FOR( ch = 0; ch < CPE_CHANNELS; ch++ )
+        {
+            IF( EQ_16( sts[ch]->hTcxEnc->tcxMode, TCX_20 ) )
+            {
+                length = sts[ch]->hTcxEnc->L_frameTCX;
+                move16();
+            }
+            ELSE
+            {
+                length = shr( sts[ch]->hTcxEnc->L_frameTCX, 1 );
+            }
+            FOR( k = 0; k <= ( ( sts[ch]->core == TCX_20_CORE ) ? 1 : NB_DIV ) - 1; k++ )
+            {
+                hdrm_min = s_min( hdrm_min, L_norm_arr( sts[ch]->hTcxEnc->spectrum_fx[k], length ) );
+                hdrm_min = s_min( hdrm_min, L_norm_arr( mdst_spectrum_fx[ch][k], length ) );
+            }
+        }
+
+        IF( hdrm_min != 0 )
+        {
+            q_spec = sub( add( hdrm_min, q_spec ), 1 ); /*1 guard bit to avoid over-flows*/
+        }
+
         FOR( ch = 0; ch < CPE_CHANNELS; ch++ )
         {
             Word16 n_sb = NB_DIV;
-- 
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