Missing energy during IVAS low rate mode

Basic info

• Float reference:
  • Encoder (float):6432cc34
• Fixed point:
  • Encoder (fixed):0cb1008

Bug description

The ACELP core synthesis energy can get very attenuated (almost disappearing) when the low rate mode is used (< 7.2kbps).

The figure below show the issue, from top to bottom :

• Float synthesis
• secondary channel bitrate
• float acelp core synthesis spectrogram
• fixed point acelp core synthesis spectrogram
• Low rate mode flag

Ways to reproduce

-stereo 2 16400 48 C:\Temp\dp01a1s06.wav bit

Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-xxxx