Question: In the EVS (Enhanced Voice Services) codec, what parameters are utilized for estimating the gains of the high-frequency band signal during bandwidth extension?
Option 1: Pitch, Noise Gate Factor, Voice Activity Detection (VAD)
Option 2: Line Spectral Frequencies (LSF), Bitrates, Adaptive Codebook Gain
Option 3: Pitch, Noise Gate Factor, Voice Factor, Classification Parameter, Linear Predictive Coding (LPC)
Option 4: Algebraic Codebook Indices, Frame Energy, Spectral Slope
Explanation: The correct answer is Option 3 because the gains of the high-frequency band signal are estimated using a combination of parameters including pitch (for periodicity), noise gate factor (to adjust for background noise), voice factor (indicating voice characteristics), classification parameter (helping in signal type classification), and Linear Predictive Coding (LPC) coefficients (which model the vocal tract). These parameters collectively enable accurate estimation of high-frequency band gains, crucial for effective bandwidth extension.