Question: In EVS (Enhanced Voice Services) codec, when the TNS (Transformed Noise Shaping) flag is set to 1 and the configuration allows for up to 2 filters, how are the parameters for the second filter indicated in the bitstream if only one filter is active?
Option 1: An additional single bit is transmitted indicating the filter order for both filters.
Option 2: The order of the first filter is set to 0 and its coefficient set to 0, implying the first filter is disabled.
Option 3: A separate Huffman-coded message is sent to specify the inactivity of the second filter.
Option 4: The bitstream includes a reserved byte indicating the number of active filters.
Explanation: According to the EVS codec specifications for TNS parameters, if the configuration allows for up to 2 filters but only one is active, the inactivity of the first filter (implying only the second filter is active) is indicated by setting the order of the first filter to 0 and its coefficient set to 0. This approach efficiently utilizes bitstream space while clearly signaling the operational state of each filter.