MDCT MC Decoder: spectral differences in BASOP decoder for format conversion

Basic info

• Float reference:
  • Encoder (float): 957cd45f
  • Decoder (float): 957cd45f
• Fixed point:
  • Encoder (fixed): n/a
  • Decoder (fixed): 480834a3

Bug description

When decoding a multi-channel (MCT) bitstream with format conversion (here: 5.1 --> 7.1+4), there are block-wise spectral differences in the background noise visible compared to float. While in float the noise-level is relatively constant across the complete spectrum, in BASOP the noise-level drops for various blocks.

BASOP:

Float:

A possible culprit could be the conversion or equalization, e.g. ivas_ls_setup_conversion_process_mdct() or a similar function in ivas_out_setup_conversion.c.

Ways to reproduce

IVAS_dec 7_1_4 48 ltv48_MC51.wav_Multi_channel_5_1_at_384_kbps_48kHz_in_48kHz_out_7_1_4_out_JBM_Prof_5.192 out.wav

Bitstream: ltv48_MC51.wav_Multi_channel_5_1_at_384_kbps_48kHz_in_48kHz_out_7_1_4_out_JBM_Prof_5.zip