Question: In a DTX/CNG scheme for EVS (Enhanced Voice Services) codec, what triggers the transmission of a new SID (Silence Insertion Description) frame when the adaptive SID update rate based on SNR fluctuations is insufficient?
Option 1: A sudden change in spectral tilt of the background noise, detected after a minimum number of consecutive inactive frames following an active talk spurt.
Option 2: Exceeding a predefined threshold of energy variation within consecutive NO_DATA frames.
Option 3: Reaching a maximum limit for the adaptive SID rate parameter (rSID) without significant SNR fluctuations.
Option 4: Detection of linear prediction coefficients (LPCs) indicating active speech in an inactive frame.
Explanation: The correct answer is Option 1 because, according to the provided context, a new SID frame is triggered by detecting a sudden change in the spectral tilt of the background noise. This detection occurs after analyzing at least 5 consecutive inactive frames following an active talk spurt to ensure the computation reflects the background noise accurately. The spectral tilt change is identified through reflection coefficients derived from LPCs and compared against a threshold, triggering a new SID frame if exceeded, alongside other conditions like a minimum number of NO_DATA frames. This approach enhances the DTX/CNG scheme by capturing perceptual changes in background noise beyond mere SNR fluctuations.