Question: In the EVS (Enhanced Voice Services) codec, when operating in Harmonic Mode at lower bitrates (e.g., 24.4 kb/s and 32 kb/s), what approach is typically taken regarding coding up to the Nyquist frequency due to insufficient bits?
Option 1: Always prioritize coding up to the Nyquist frequency, even if it means reducing the quality of the lower sub-bands.
Option 2: Stop short of coding right up to the Nyquist frequency to maintain better overall signal quality.
Option 3: Dynamically adjust the bitrate to always accommodate full-spectrum coding up to the Nyquist frequency.
Option 4: Apply additional noise filling to compensate for the insufficient bits, ensuring coding up to the Nyquist frequency.
Explanation: In Harmonic Mode, especially at lower bitrates (like 24.4 kb/s and 32 kb/s), there are often insufficient bits to encode the full signal without compromising quality. To mitigate this, the approach is to stop short of coding right up to the Nyquist frequency. This ensures that the encoded part of the signal maintains a higher quality, which is particularly important for preserving the harmonic characteristics of voice signals in the lower sub-bands, even if it means not utilizing the full frequency range.