Audio format and codecs

Hello guys.
Im not that good with audio formats. I already created a test IVR menu and i need to create the audio. which format and which codecs do i have to use? do i need to register those audio files somewhere or just put them to the to /var/lib/asterisk/sounds/ and thats it?
Thanks

Any format that can be converted to the codec in use, but ideally ever codec format in use.

You don’t need to register.