bad quality for ISM-2 at 16.4kbps

Basic info

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

Bug description

For some signal, the fixed point synthesis quality of ISM-2 at 16.4 kbps is worst than the floating point.

in the next figures, we see examples of the left channel, but similar cases can be observed on the right channel as well. The problem is that the shape of the synthesis is very different, leading to a very different synthesis quality.

From top to bottom :

• Original (Left channel)
• Float synthesis
• Fixed synthesis
• spectrum

Ways to reproduce

G6S6

IVAS_cod -ISM 2 NULL NULL 16400 48 G6S6.wav bit
IVAS_dec_flt EXT 48 bit out.fxflt.wav

IVAS_cod_flt -ISM 2 NULL NULL 16400 48 G6S6.wav bit.flt
IVAS_dec_flt EXT 48 bit.flt out.fltflt.wav