Question: What is the primary reason for utilizing a noise estimator in the decoder for Frequency Domain Comfort Noise Generation (FD-CNG) in Enhanced Voice Services (EVS)?
Option 1: To reduce computational complexity by avoiding spectral analysis.
Option 2: To capture the fine spectral structure of background noise not conveyed by SID frames.
Option 3: To synchronize encoder and decoder clocks in real-time communications.
Option 4: To enhance speech quality by introducing artificial noise floor.
Explanation: The correct answer highlights the key challenge addressed by the noise estimator in FD-CNG. Since SID frames can only reproduce the smooth spectral envelope of background noise and not its fine spectral structure, a noise estimator is used at the decoder to recover this missing information directly, ensuring a more seamless transition between active and comfort noise frames and improving overall audio quality.