Voice Changer - Web
This challenge provided a link to a voice changer web application. 
The request contained parameters that were related to the pitch and the uploaded recording.
In the server's response we can see that the web application ran ffmpeg command which is a video/audio handling software, in the operating system shell.
Since it looked like the web app ran commands in the operating system and used the pitch value as part of the command, I tried breaking out of it and running additional command.
uoftctf{Y0UR Pitch IS 70O H!9H}