Question: In Multi-mode FD Bandwidth Extension (BWE) decoding for Enhanced Voice Services (EVS), how is the full-band (FB) signal synthesized in FB mode?
Option 1: Solely based on the decoded low band envelope from the received bitstream.
Option 2: Based on the energy ratio of the current frame and the generated Super Higher Band (SHB) frequency excitations, combined with the low band envelope.
Option 3: Exclusively using the classified Higher Band (HB) signal for WB signals without considering the low band signal.
Option 4: By directly copying the decoded Super Higher Band (SHB) signal for SWB signals into the full-band frequency range.
Explanation: In FB mode of Multi-mode FD BWE decoding, the synthesis of the full-band (FB) signal involves utilizing both the energy ratio of the current frame and the generated SHB frequency excitations, combined with the low band envelope, ensuring a comprehensive reconstruction of the full-band signal.