Question: In the EVS codec's post-filter, under what condition(s) are the long-term normalized noise gain (`γ_tilde`) updates performed, and what is the value of `β_post` when this update occurs but an active signal is not detected or `γ_tilde` ≥ 25.0?
Option 1: Updates occur in GSC mode with any signal activity; `β_post` = 0.65 in the specified non-update condition.
Option 2: Updates occur only in UC mode with no signal activity; `β_post` = 0.15 when not an active signal or `γ_tilde` ≥ 25.0.
Option 3: Updates happen in both UC and GSC modes regardless of signal activity; `β_post` = 1 in the non-update condition scenario.
Option 4: No updates occur if `γ_tilde` is below a certain threshold with active signals; `β_post` always defaults to 0.55.
Explanation: According to specifications, the long-term normalized noise gain (`γ_tilde`) is updated only in UC mode with no signal activity. In scenarios without an active signal or `γ_tilde` ≥ 25.0, `β_post` is set to 0.15, highlighting nuanced handling of noise gain for optimized voice service quality.