Question: For a Narrowband (NB) signal encoded at 13.2 kbit/s with the high frequency dynamic range flag set to 0, how many subframes are typically used per frame in the Enhanced Voice Services (EVS) codec?
Option 1: 1 subframe (used for audio signals requiring long-time support for better frequency resolution)
Option 2: 2 subframes (common for inactive signals or when specific flags indicate no high-frequency spectral correlation)
Option 3: 4 subframes (specifically used for Super Wideband (SWB) unvoiced mode at the same bit rate)
Option 4: The number of subframes is dynamically adjusted based on the signal's dynamic range
Explanation: According to the EVS codec specifications, for NB and WB signals encoded at 13.2 kbit/s, if the high frequency dynamic range flag is 0 (indicating no presence of high-frequency spectral correlation), or in cases of inactive signals, 2 subframes are utilized per frame. This setup optimizes the encoding process for such signal conditions without compromising on the necessary detail for accurate playback.