issue for ISM4 at 48 kbps with dtx on

Basic info

• Float reference:
  • Encoder (float): fbeb5ef8
  • Decoder (float): fbeb5ef8
• Fixed point:
  • Encoder (fixed): de24537b

Bug description

when using the ISM format with 4 objects, the dtx/cng seems to have trouble with the noisy channel, sometimes the energy going down to almost nothing as shown below for channel 3. With the same channel, we can also hear clicks (the 2 first circles, and in the second figure) that are present with or without dtx

from top to bottom:

• Channel 3 floating point
• Channel 3 fixed point
• difference
• spectrum

Ways to reproduce

Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-1160

IVAS_cod -dtx -ISM 4 NULL NULL NULL NULL 48000 48 C:\Temp\bm6ba1s05.wav bit
IVAS_dec_flt EXT 48 bit out.fxflt.wav

IVAS_cod_flt -dtx -ISM 4 NULL NULL NULL NULL 48000 48 C:\Temp\bm6ba1s05.wav bit.flt
IVAS_dec_flt EXT 48 bit.flt out.fltflt.wav