Question: In Comfort Noise Generation (CNG) for Enhanced Voice Services (EVS), how is random noise generated for frequencies above the core bandwidth in the context of CLDFB (Complex Low-Delay Filter Bank)?
Option 1: By replicating the noise spectrum from the core bandwidth and applying a fixed amplification factor.
Option 2: Through deterministic calculation based on the input signal's spectral characteristics.
Option 3: By generating random Gaussian noise of zero mean and variance, separately for the real and imaginary parts of the CLDFB coefficients.
Option 4: Using an adaptive algorithm that adjusts noise levels based on the instantaneous signal-to-noise ratio (SNR).
Explanation: This is correct because, according to the principles outlined for Comfort Noise Generation in the frequency domain, specifically for frequencies beyond the core bandwidth handled by CLDFB, the method involves generating random Gaussian noise. This approach ensures that the comfort noise accurately mimics the statistical properties of natural background noise, enhancing the perceptual quality of the voice service. The generation of noise separately for the real and imaginary parts with zero mean and variance is a key aspect of this technique, allowing for a realistic simulation of ambient noise conditions.