Question: In the Non-Linear Excitation Generation process for EVS (Enhanced Voice Services) codec, what condition affects the application of sign reversal when processing a voiced frame?
Option 1: The type of subframe (first half or second half)
Option 2: The number of samples in the frame (e.g., 160 samples)
Option 3: The comparison between the current and previous scale factor parameters
Option 4: The sum of voice factors over subframes being below a specific threshold (dependent on the number of subframes per frame)
Explanation: In the context of Non-Linear Excitation Generation for EVS, sign reversal is conditionally applied based on the frame type (voiced) and the sum of voice factors over subframes. Specifically, if the frame is voiced and this sum falls below a threshold (which varies with the number of subframes per frame, e.g., 0.70 for five subframes or 0.78 for four), sign reversal is not performed. This highlights the adaptive nature of the EVS codec in handling different voice characteristics to optimize output quality.