Question: In EVS (Enhanced Voice Services) codec, for Narrowband (NB) inputs, what additional condition must be satisfied when detecting an energy decrease after a spike, besides a maximum energy variation higher than 30 dB?
Option 1: The mean spectral flatness must be below a certain threshold.
Option 2: The mean correlation must not be too high.
Option 3: The signal-to-noise ratio (SNR) must exceed a predefined value.
Option 4: The frame length must be extended to accommodate the spike.
Explanation: In the context of detecting energy decreases after spikes for EVS codec, specifically for Narrowband inputs, ensuring the mean correlation is not too high is crucial. This condition helps in accurately identifying significant temporal events (like castanets) followed by rapid energy decay, preventing unnecessary UC mode activations. It highlights the importance of correlation analysis in signal processing for voice services, impacting how efficiently the codec manages transient audio events.