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Energy missing in BWE for DFT stereo at 24.4kbps (TD stereo not triggered)

Basic info

  • Float reference:
  • Fixed point:
    • Encoder (fixed): 1df326bb
    • Decoder (fixed):

Bug description

Some energy is missing in the BWE for the fixed point synthesis when compared to the floating point synthesis. The problem is present in both channels, but not at the same time. When that happens, it's from 8kHz and up.

Just for information, below is the MLD and Peaq diff scores when compared to original and when compared between fix and float. In all cases, this case would be hard to detect. (@norvell , @fotopoulou, @malenovsky, @jelinek )

MLD and Peaq compared to original and then difference : image

MLD float-Fixed : 3.42 for Left channel and 4.01 for right channel

Next figure, from top to bottom:

  • Spectrogram left channel float
  • Spectrogram right channel float
  • Spectrogram left channel fixed
  • Spectrogram right channel fixed

image

Ways to reproduce

Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-1195

IVAS_cod -STEREO 24400 48 ap01a2s05.wav bit
IVAS_dec_flt STEREO 48 bit out.fxflt.wav

IVAS_cod_flt -STEREO 24400 48 ap01a2s05.wav bit
IVAS_dec_flt STEREO 48 bit out.fltflt.wav