Presence of noise for stereo at 32kbps, low level samples

Basic info

• Float reference:
  • Encoder (float): 964def597
  • Decoder (float):
• Fixed point:
  • Encoder (fixed): 437601cb
  • Decoder (fixed):

Bug description

During the characterization tests, several anomalies were identified. A persistent issue, observed across multiple samples and still present in the current implementation of the fixed-point codec, is the presence of an buzziness/electrical noise/quantization noise at a bitrate of 32 kbps.

For the reference samples stored in the Box folder, this artifact is most noticeable between 2 and 3 seconds. When monitoring the stereo signal, the distortion feels as a coarse phantom noise. If you compare the left channel of the float and fixed versions, the buzziness becomes very clear. It is important to note that only FD stereo mode was employed for these samples.

Ways to reproduce

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

cp Mp01a4s03.c01.wav loc_dir\Mp01a4s03.c01.wav
python scale_pcm.py loc_dir 0.316

IVAS_cod -stereo 32000 48 loc_dir\Mp01a4s03.c01.wav bit.fx
IVAS_dec STEREO 48 bit.fx loc_dir\Mp01a4s03.c01.fxfx.wav

IVAS_cod_flt -stereo 32000 48 loc_dir\Mp01a4s03.c01.wav bit.flt
IVAS_dec_flt STEREO 48 bit.flt loc_dir\Mp01a4s03.c01.fltflt.wav

python scale_pcm.py loc_dir 3.16