Why the PBX rejects a file
Telephony is narrowband: G.711 is 8000 samples a second, one channel. A 44.1 kHz stereo file is either rejected or transcoded on the fly, costing CPU and quality. So prompts are converted to 8 kHz mono in advance; for Asterisk it is handy to also ship .alaw or .ulaw files, which are sent to the channel with no processing at all.
How to make prompts clear
- Even out loudness: a quiet greeting after loud hold music sounds poor.
- Pick hold music with little deep bass and a clear melody: after G.711 and G.729 only the mid range survives.
- The telephone filter lets you hear in advance how it will sound on a handset.
Voice menu
Prompt texts and the dialplan come from the IVR builder.