Use sox on linux to convert the audiofile
sox <filename> -t raw -b 16 -r 32000 output.sln
changing the extension to sln32 (sound quality?)
mv output.sln output.sln32
moving to correct location so asterisk config can find it
mv output.sln32 /var/lib/asterisk/sounds/custom
change file permissions
chown asterisk:asterisk output.sln32
## extensions example
exten => 15,1,NoOp
same => n,PlayBack(/var/lib/asterisk/sounds/custom/output)
same => n,wait(1)
same => n,Hangup() ref https://docs.asterisk.org/Operation/Asterisk-Audio-and-Video-Capabilities/