Question: In NELP (Noise-Excited Linear Prediction) Encoding for Enhanced Voice Services (EVS), what is the primary purpose of analyzing and comparing the spectral characteristics of the shaped excitation with the original residual signal?
Option 1: To select a filter that further shapes the excitation's spectral characteristics for optimal performance, enhancing voice quality in unvoiced segments.
Option 2: To adjust the quantization scheme for LSP (Line Spectral Pairs) to match the Unvoiced Coding (UC) mode more accurately.
Option 3: To determine the optimal sub-frame size for dividing the residual signal, reducing bit rate without compromising quality.
Option 4: To generate a sparse excitation that mimics the characteristics of voiced speech segments, improving overall speech naturalness.
Explanation: The correct answer is Option 1 because, in the NELP encoding process, analyzing and comparing spectral characteristics after shaping the sparse excitation helps select an appropriate filter to adjust the excitation's spectral characteristics. This step aims to achieve optimal performance in capturing unvoiced speech segments, directly enhancing voice quality in these segments.