Plug your iOS device into a stereo system and then, use the foldback function with one of the reverb effects, you can do vocal exercises, get everyone's attention, make announcements.
It gives you a chance to easily confuse your friend with phone calls, voice chats of game or social apps and so on.
The app can change your voice in real time: speaking to the microphone of the iOS device, the sync output in the speaker is changed voice.
Even you can send the playing sound to your friends with talkback function of social apps.
With the voice-changing function and reverb effect function, you can record very special audio files.