SBA 16.4 DTX ON decoder issue with p800-4 cat3

Basic info

• Float reference:
  • Encoder (float):20250826_branch_release_characterization_testing_ivas-float-update
  • Decoder (float):20250826_branch_release_characterization_testing_ivas-float-update
• Fixed point:
  • Encoder (fixed):N/A
  • Decoder (fixed):20250826_branch_release_characterization_testing_main

Bug description

Strange noise during DTX mode in SBA at very low bitrates like 16.4 kbps and 24.4 kbps.

The issue can be reproduced with p800-4 category 3 item (even without introducing packet loss). The concatenated input and encoded packet file is present at _EXTERNAL_IVAS_CHAR_MC_\issues\basop-issue-1996 folder.

The codec goes into DTX mode first time at frame 139, but the issue happens at around frame 219 (SID frame) and after that every frame has a discontinuity which can be seen in the spectrogram and also very obviously audible.

The issue is present at the output of SCE itself so its most likely a SCE decoder issues.

Tagging @multrus as well.

Ways to reproduce

Box folder: ._EXTERNAL_IVAS_CHAR_MC_\issues\basop-issue-1996

Folder contains: HOA2 input, encoded packet file (same packet can be used with FL and FX decoder and the issue is only present in FX decoder out), SCE decoder output

Decoder cmd: ivas_dec.exe FOA 48 in.pkt out.wav OR ivas_dec.exe BINAURAL 48 in.pkt out.wav