Question: In EVS (Enhanced Voice Services) codec, what is a common condition for both Wideband (WB) and Narrowband (NB) inputs to select the Uncoded (UC) mode for the current frame?
Option 1: High normalized correlation and energy concentrated in low frequencies
Option 2: Presence of sudden energy increase in the current frame
Option 3: The current frame being in a segment following voiced offset with raw coding mode selected previously
Option 4: Low normalized correlation and energy concentrated in high frequencies
Explanation: In the context of EVS codec's UC mode selection, both for WB and NB inputs, it is crucial to ensure that only frames without periodic content are coded with this mode. A key indicator of non-periodic content is when the energy is concentrated in high frequencies coupled with low normalized correlation, which suggests a lack of repeating patterns (periodicity) in the signal, making **Option 4** the correct choice. This condition helps in identifying frames suitable for UC mode, which doesn't utilize adaptive codebook or long-term prediction, optimizing encoding for non-periodic signals.