Upto 15dB spectral difference between fixed- and floating-point output when decoding an OSBA (ISM4_HOA3) bitstream at 80kbps

Basic info

• Encoder (float): d18cbee3 (ivas-float-update)
• Decoder: 074e9116 (tag: 20241023_Ittiam_Decoder_Release_subjective_Testing)

Input format: ISM4_HOA3

Input level: -16LKFS

Encoding bitrate: 80kbps

Bug description

As seen in the following screen captures, major spectral discrepancies were observed in the frequency range from 1 to 5 kHz in the fixed- floating-point decoded output. Following plot illustrates the different spectra in channel#9. Red is fixed-point output, orange/yellow is floating point output. Time range is between 8.7 to 8.8s.

Ways to reproduce

Supporting files: ...\Box\EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-1023

Command line:

./IVAS_cod_ref -no_delay_cmp -ism_sba 4 3 in_0.csv in_1.csv in_2.csv 80000 48 in_3.csv in.wav bit
./IVAS_dec -no_delay_cmp EXT 48 bit fx.wav
./IVAS_dec_ref -no_delay_cmp EXt 48 bit fl.wav