Question: In the Enhanced Voice Services (EVS) codec, what are the two primary coding modes that can transition into each other within the same bit rate and audio bandwidth?
Option 1: CELP (Code-Excited Linear Prediction) coding mode and MDCT (Modified Discrete Cosine Transform) coding mode
Option 2: AMR-WB IO (Adaptive Multi-Rate Wideband Input/Output) mode and LP (Linear Predictive) coding mode
Option 3: PCM (Pulse Code Modulation) coding mode and DPCM (Differential Pulse Code Modulation) coding mode
Option 4: G.729 coding mode and G.723 coding mode
Explanation: The EVS codec's flexibility in switching between different coding modes within the same bit rate and audio bandwidth is crucial for adapting to varying network conditions while maintaining voice quality. CELP is effective for speech, focusing on the excitation signal, while MDCT is beneficial for music and mixed content, leveraging transform coding. This dual-mode capability enhances the EVS codec's performance in handling diverse audio inputs efficiently.