Question: What is the primary purpose of the low-pass FIR filter with a cut-off frequency at 6.4 kHz in the EVS (Enhanced Voice Services) codec when converting input signals of 16, 32, or 48 kHz to 12.8 kHz?
Option 1: To amplify the signal for better transmission quality
Option 2: To remove high-frequency components above 6.4 kHz before down-sampling to prevent aliasing
Option 3: To introduce a deliberate delay for synchronization purposes
Option 4: To compress the signal for reduced bandwidth usage
Explanation: The correct answer is because, in converting sampling frequencies, applying a low-pass filter before down-sampling prevents aliasing. Aliasing distorts the signal when high-frequency components are folded back into the lower frequency range during sampling rate reduction. Filtering out frequencies above 6.4 kHz ensures only appropriate components are retained for the target 12.8 kHz rate, maintaining signal integrity.