Question: In EVS (Enhanced Voice Services) codec, as per 3GPP standards, how is the low-band comfort noise synthesized for speech signals?
Option 1: By filtering the scaled combined excitation signal through a smoothed Linear Predictive (LP) synthesis filter.
Option 2: Through direct modulation of the input audio signal without any filtering process.
Option 3: By applying a non-linear transformation to the output of the speech encoder.
Option 4: Using an unsmoothed Infinite Impulse Response (IIR) filter on the error signal.
Explanation: In the context of Enhanced Voice Services (EVS) codec, synthesizing low-band comfort noise involves enhancing the perceptual quality of the speech signal during silent periods. The correct approach is to filter the scaled combined excitation signal through a smoothed Linear Predictive (LP) synthesis filter, ensuring the synthesized noise matches the spectral characteristics of the background noise in the original speech signal for a natural listening experience.