you mean a Vocoder?
auto-tune just brings a person singing up to the right pitch it is intended to hit
Vocoders make that robotic sound
vocoder is running your voice through a synth to control the amplitude of the synth
autotune is a device that detects what notes you're supposed to be singing and modulates your voice to the correct pitches
autotune is what breathe carolina used, it's what kayne uses, it's what owl city uses, it's what attack attack uses
it's basically used by someone that can't sing but wants to be able to sing
and i do know what i'm talking about, i've worked with bands that have used it before, my brothers old band used it because their singer smoked to much and ruined his voice