Question: In EVS (Enhanced Voice Services) codec, how is the weighed synthesis filter state updated during a sampling rate switch from 12.8 kHz to 16 kHz at bit-rates above 8 kbps but not including 13.2, 32, or 64 kbps?
Option 1: It is always set to zero for any sampling rate change.
Option 2: The state is recomputed by filtering the resampled LPC synthesis filter state through a specific filter and calculating the error with the input weighted signal.
Option 3: The memory states are updated in the previous frame as usual, ignoring the difference in sampling rates.
Option 4: A linear interpolation between the two sampling rates' states is performed to update the filter state.
Explanation: According to EVS codec specifications for handling sampling rate switches (e.g., from 12.8 kHz to 16 kHz) at specific bit-rates, the weighed synthesis filter state undergoes a re-computation process. This involves filtering the resampled LPC synthesis filter state and then computing the error between the filtered signal and the input weighted signal. This approach ensures adaptive adjustment of the filter state to accommodate the change in sampling rate effectively, especially at bit-rates that require more precise handling (i.e., above 8 kbps but excluding specific rates like 13.2, 32, or 64 kbps).