Question: In EVS (Enhanced Voice Services) codec, when FD-CNG (Fullband Discontinuous Transmission Comfort Noise Generation) is triggered in DTX-on (Discontinuous Transmission) mode, how are the FD-CNG noise levels utilized for CNA (Comfort Noise Analysis) noise estimation?
Option 1: By recalculating the entire spectral structure of the background noise during inactive phases.
Option 2: Directly, utilizing the captured fine spectral structure from active phases and updated spectral envelope from SID information during inactive parts.
Option 3: By averaging the noise levels from both active and inactive phases before FD-CNG is triggered.
Option 4: Through an additional signal processing step that combines past and present noise floor estimates.
Explanation: This is correct because, in the context of EVS codec operations, when FD-CNG is triggered in DTX-on mode, the existing fine spectral structure captured during active phases can be directly utilized for CNA noise estimation. Additionally, updates to the spectral envelope during inactive parts, facilitated by SID information, enhance this process without requiring a full recalculation or additional processing steps as suggested in other options.