Increased noise level in BASOP decoder for band-limited input from float encoder

Basic info

• Float reference:
  • Encoder (float): e15ad0ad
  • Decoder (float): e15ad0ad
• Fixed point:
  • Decoder (fixed): d4fd91a6

Bug description

There is a clear increase in background noise (about 20 dB) at 64 kbps using 16 kHz input and 48 kHz output. See the spectrograms:

Not sure how widely this happens but at least this exact example case shows the effect clearly. Audibility of the effect is not significant at least for me but this example case also has MLD score over 10 which is a bit of an outlier on the decoder side constant bitrate cases. However, I would say that if input signal sample rate was limited to 16 kHz, then output signal should not synthesize content above 8 kHz either.

Ways to reproduce

IVAS_cod_ref -masa 2 ltv48_MASA2TC.met -max_band swb  64000 16 ltv16_MASA2TC.wav test_0284.bs
IVAS_dec EXT 48 test_0284.bs 0284_ltv16_MASA2TC.wav_64k_16-48___EXT.wav