Audible glitch sound in decoded transport audio with MASA 2TC rate switching and FER

Basic info

• Commit SHA: 9af190bf
• Platform: All

Bug description

As part of BASOP verification work, there was a large difference noted in rate switching + FER condition of MASA. With some digging, it was found that there is a clear glitch in float reference which is not present in BASOP code. Further testing shows that this is also present in IVAS Codec main. Here is a plot showing the glitch

and it is also clearly audible. BASOP main instead seems to become "quiet" at the same time if this gives a clue to solution.

Not sure where the issue is other than probably being part of the core. Same processing without FER does not provoke such artifacts so this is another clue for the problem. So maybe PLC or core rate switching related. I did not test if this would also happen without MASA being part of it.

Ways to reproduce

This can be reproduced using the following error profile and MASA files in main

ep_10pct.g192

stv2MASA2TC48c.wav

stv2MASA2TC48c.met

with a rate switching profile attached here

generic_start_384k_20frames.bin

Then run

./IVAS_cod -masa 2 stv2MASA2TC48c.met -max_band fb generic_start_384k_20frames.bin 48 stv2MASA2TC48c.wav debug.bs
./eid-xor -fer -vbr -bs g192 -ep g192 debug.bs ep_10pct.g192 debug.bs_eid
./IVAS_dec EXT 48 debug.bs_eid out.wav

and you will have the glitch in the wave output at about 2 s. You can also use any other output format but using EXT does not add any rendering on top of the transport channels.