Question: In EVS (Enhanced Voice Services) LP-CNG decoding, when a WB (WideBand) SID frame is received while the decoder operates in SWB (Super WideBand) mode, how is the energy parameter for high-band CN (Comfort Noise) synthesis handled?
Option 1: The high-band energy parameter is decoded directly from the WB SID frame.
Option 2: The high-band energy parameter is set to a default value since WB frames do not carry this information in SWB mode.
Option 3: The energy parameter for high-band CN synthesis is extrapolated from the low-band CN synthesis signal.
Option 4: The decoder switches back to WB mode to synthesize comfort noise only for the low-band.
Explanation: This question requires understanding of how EVS handles comfort noise synthesis, particularly in mixed bandwidth scenarios. The correct answer, Option 3, reflects the specification's detail that when in SWB mode, receiving a WB SID frame still necessitates generating high-band CN, which is done by extrapolating from the low-band CN synthesis signal since direct transmission of high-band CN parameters isn't synchronized with low-band parameters. This showcases the decoder's adaptive handling to maintain comfort noise quality across different bandwidth modes.