Question: In EVS (Enhanced Voice Services) codec, according to 3GPP standards, how are residual bits decoded for bitrates of 13.2 kbps and above, specifically regarding the refinement of spectral values?
Option 1: All spectral values are refined using a fixed 2-bit allocation per value.
Option 2: Only non-zeroed spectral values are refined, with each utilizing a dynamic bit allocation based on preceding bits.
Option 3: The first three bits refine the global gain, then 1 bit per non-zeroed spectral value is used for refinement, with at least 2 bits left potentially refining a zeroed value.
Option 4: Zeroed and non-zeroed spectral values are refined together using a joint 3-bit allocation.
Explanation: This option accurately reflects the process described for bitrates of 13.2 kbps and above in the context of EVS codec's residual bits decoding. It correctly identifies the initial use of three bits for global gain refinement, followed by a one-bit-per-non-zeroed-spectral-value approach for further refinement, with a conditional refinement for zeroed values if sufficient bits remain.