Question: In the EVS (Enhanced Voice Services) codec, what determines the selection of the impulse response for anti-sparseness processing in the algebraic codevector post-processing procedure?
Option 1: Decoded adaptive codebook gain, previous algebraic codebook gain, current and past adaptive codebook gains, coding mode, and bit rate.
Option 2: Only the decoded adaptive codebook gain and the coding mode.
Option 3: The bit rate alone, with higher rates corresponding to stronger modifications.
Option 4: A fixed schedule based on the subframe index, without adapting to signal characteristics.
Explanation: The selection of the impulse response for anti-sparseness processing in EVS codec's algebraic codevector post-processing is adaptively determined by a combination of factors. These include the decoded adaptive codebook gain (reflecting current signal characteristics), the previous algebraic codebook gain (providing context), the current and past adaptive codebook gains (indicating trends or consistency in the signal), the coding mode (affecting how the signal is processed), and the bit rate (influencing the balance between quality and bandwidth usage). This multifaceted approach allows for a more nuanced adjustment of anti-sparseness processing to suit varying signal conditions, enhancing perceptual quality.