# Bug Description When running the MC param upmix in the BASOP encoder, an underflow occurs on **line 504** in `ivas_mc_paramupmix_enc_fx.c` inside the function `quantize_pars_fx()`: ```c Word16 exp_var2 = 0; move16(); Word32 var2 = BASOP_Util_Add_Mant32Exp(v_fx[iv], exp_v, L_negate(data_fx[iq1]), 31 - Q28, &exp_var2); var2 = L_abs(var2); ``` In **frame 77** (and others), the value of `var2` reaches the minimum 32-bit integer value (`-2147483648`). Passing it to the `L_abs()` function results in `2147483647` due to integer underflow. - Fixed point: - Encoder (fixed): 012d348977afd246f93a41c936e07d7646c12eb3 # Ways to reproduce ```bash ./IVAS_cod -mc 7_1_4 160000 48 tv/stv714MC48c.wav bit ``` This issue has been first observed and reported in https://forge.3gpp.org/rep/sa4/audio/ivas-basop/-/merge_requests/1229