Large differences between BASOP and float for critical item in MDCT-stereo @96kbps

Basic info

• Float reference:
  • Encoder (float):ecb2d1dd
  • Decoder (float):ecb2d1dd
• Fixed point:
  • Encoder (fixed):d818c148

Bug description

For the particular items very large differences are observed between BASOP and code version, which seems to be the case throughout the majority of the item. For reference see below the spectrum for the left channel for 3 consecutive frames starting from timestamp 0.240 ms, red represents BASOP and green is float:

0.240 ms

0.260 ms

0.280 ms

The input signal is of higher loudness (approx -13 LFKS), so I also tested with normalizing the input to -26 LKFS and the issue is still present.

Ways to reproduce

Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-1308

IVAS_cod -stereo -max_band fb 96000 48 emese_48_STEREO.pcm emese_stereo_b96_fb_cbr.192
IVAS_dec STEREO 48 emese_stereo_b96_fb_cbr.192 emese_stereo_b96_fb_cbr.dec.STEREO.wav