Difference in BWE at 13.2 kbps for ISM-1

Basic info

• Encoder (float): 311956f3
• Encoder (fixed): 6362e224
• Decoder (float in both cases): 311956f3

Bug description

The fixed point encoder introduces a different BWE structure compared to the floating point for ISM-1 at 13.2 kbps. This also means that all mode/format using the core at 13.2 kbps ( or bitrates close to that) will suffer similar issues.

from top to bottom:

• Spectrogram float synthesis
• Spectrogram fixed synthesis
• difference signal
• Spectrum of float (red) and fixed (blue)

Ways to reproduce

Input files located in box : issue-1091

IVAS_cod_flt -ISM 1 input.wav.0.csv 13200 48 input.wav bit.flt

IVAS_cod_fx -ISM 1 input.wav.0.csv 13200 48 input.wav bit.fx

IVAS_dec_flt EXT 48 bit.flt syn.flt.wav

IVAS_dec_flt EXT 48 bit.fx syn.fx.wav