Question: In EVS (Enhanced Voice Services) codec during SWB (Super Wide Band) mode DTX/LP-CNG operation, what triggers the transmission of a SWB SID frame containing both low and high band parameters, aside from the first SID frame after active frames or within the high band analysis initialization period?
Option 1: A change in the energy ratio between low and high band signals by more than 1dB.
Option 2: A deviation in the energy relationship between the low and high band signals at the current frame from that at the previous SWB SID frame by more than 3dB.
Option 3: The occurrence of a step update to the smoothed low band log average energy.
Option 4: A bandwidth switch from NB (Narrow Band) to WB (Wide Band).
Explanation: This is correct because, according to the EVS codec's operation in SWB mode DTX/LP-CNG, a SWB SID frame is transmitted when the energy ratio between the low and high band signals changes significantly (by more than 3dB) from the previous SWB SID frame. This ensures efficient use of bandwidth while maintaining perceptual quality. The other options either describe incorrect triggers or thresholds for SWB SID frame transmission in this context.