Question: What is the primary purpose of the "magic number" in the EVS (Enhanced Voice Services) header, as defined by 3GPP specifications?
Option 1: To indicate the version of the file format and ensure compatibility across different EVS implementations.
Option 2: To specify the bitrate of the encoded audio signal for efficient transmission.
Option 3: To determine the number of supported audio channels in a multi-channel configuration.
Option 4: To authenticate the source of the audio file for security purposes.
Explanation: The "magic number" ("#!EVS_MC1.0\n" or 0x23214556535f4d43312e30) serves as a unique identifier for EVS files, incorporating a version number ("1.0" in this case). This ensures that the file format is recognized and interpreted correctly by compatible devices or software, highlighting its role in maintaining compatibility across different implementations of the EVS standard.