Question: What is the primary purpose of Comfort Noise Addition (CNA) in Enhanced Voice Services (EVS) codec for bit-rates up to 13.2 kbps?
Option 1: To enhance speech clarity by reducing background noise in decoded audio signals.
Option 2: To mask coding artifacts by generating and adding artificial background noise to the decoded audio signal.
Option 3: To improve the efficiency of coding clean speech at higher bit-rates.
Option 4: To enable Dual-Tone Multi-Frequency (DTMF) signaling in noisy environments.
Explanation: Comfort Noise Addition (CNA) enhances decoded speech quality, especially for low-bit-rate coded speech with background noise. It generates artificial background noise based on estimated levels and spectral shapes, adding it to the decoded signal to mask coding artifacts, thus improving overall speech perceptual quality.