Why do 3CX and legacy PBX systems reject standard MP3/WAV records?
Traditional telecom hardware networks process signals across highly constrained bandwidth arrays. System prompts and interactive voice responses (IVR) mandate a precise audio container structure: linear PCM encoding wrapped inside a WAV header, sample rate clamped to exactly 8000Hz (or 16000Hz), a bit depth matching 16-bit parameters, mapped down to a single Mono audio channel.