Question: In EVS (Enhanced Voice Services) codec, for a TCX (Transform Coded Excitation) frame, what determines the selection of the partial copy mode for constructing a partial redundant frame to enhance frame loss concealment?
Option 1: Only the mode of the immediately preceding frame and the frame class.
Option 2: The LTP (Long-Term Prediction) pitch and gain alone.
Option 3: A combination of the current frame's class, LTP pitch, but not considering previous frames' modes.
Option 4: Various parameters including the mode of the last two frames, the frame class, LTP pitch, and gain.
Explanation: The selection of the partial copy mode for TCX in EVS codec is based on a multifaceted approach, considering historical frame context (modes of the last two frames), current frame characteristics (frame class), and specific audio signal attributes (LTP pitch and gain). This comprehensive consideration ensures optimal frame loss concealment.