One of Asterisk 1.8’s many new features is a function called PITCH_SHIFT. PITCH_SHIFT allows you to change the pitch of the audio on a given channel.
Here’s a quick dial-plan example that you can use to lower the pitch of the callers voice on calls placed to SIP extension 500. You can also substitute tx for rx and the voice of the called party will be changed. You can change the voice of both the caller and the called party by substituting rx or tx with both.
The pitch of the voice can be raised or lowered by changing the number after the = sign. A value greater than 1 raises the pitch, while numbers less than 1 lower the pitch. Any number between .1 and 4 can be used.
exten => 500,1,Set(PITCH_SHIFT(rx)=.7) exten => 500,2,Dial(SIP/500) exten => 500,3,Hangup()
You can find additional documentation by running “core show function PITCH_SHIFT” at the Asterisk CLI.